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S

 
S waves
   (NASA Thesaurus)
Waves in an elastic media which cause an element of the medium to change its shape without a change in volume. Mathematically, S waves are ones whose velocity field has zero divergence. Used for secondary waves, shear disturbances, and shear waves.
S-band
   (NASA SP-7, 1965)
A frequency band used in radar extending approximately from 1.55 to 5.2 kilomegacycles per second.
SA
   (Space Flight Glossary - JPL)
Solar array, photovoltaic panels onboard a spacecraft.
sabot
   (NASA Thesaurus / NASA SP-7, 1965)
(sabot projectiles) A device fitted around or in back of a projectile in a gun barrel or launching tube to support or protect the projectile or to prevent the escape of gas ahead of it.
The sabot separates from the projectile after launching.
sabotage
   (NASA Thesaurus)
Deliberate destructive action that may be directed against property, processes, systems, organizations, governments, or people and that is intended to prevent a process, undermine a group, or interfere with progress towards a goal.
SAGE satellite
   (NASA Thesaurus)
Spacecraft for the study of stratospheric aerosols and gases. Used for Stratospheric Aerosol & Gas Experiment.
Sagitta
   (NASA SP-7, 1965)
(abbr Sge, Sgte)
See constellation.
Sagittarius
   (NASA SP-7, 1965)
(abbr Sgr, Sgtr)
See constellation.
Sagnac effect
   (NASA Thesaurus)
A phase shift (and consequent measurable rotation rate) caused by nonreciprocity (different optical path lengths) of two counterpropagating light waves traveling in the same coil in a fiber optic gyro or ring interferometer.
salt beds
   (NASA Thesaurus)
Deposits of sodium chloride and other salts resulting from the evaporation and/or precipitation of ancient oceans.
salvo launch
   (NASA SP-7, 1965)
Act of launching two or more rockets simultaneously.
sample
   (NASA Thesaurus)
Physical or biological specimens intended to be representative of the whole.
sample
   (NASA SP-7, 1965)
In statistics, a group of observations selected from a statistical population by a set procedure. See random sample.
Samples may be taken at random or systematically. The sample is taken in an attempt to estimate the population.
sampling
   (NASA Thesaurus)
Obtaining of a portion representative of the material concerned.
sandwich
   (NASA SP-7, 1965)
Of sandwich construction, as in sandwich panel, sandwich skin , etc.
sandwich construction
   (NASA SP-7, 1965)
A type of construction in which two sheets, sides, or plates are separated by a core of stiffening material, generally lightweight. See honeycomb core.
SAR
   (Space Flight Glossary - JPL)
Synthetic Aperture Radar.
Sarah
   (NASA SP-7, 1965)
(From search and rescue and homing). A radio homing device originally designed for personnel rescue and now used in spacecraft recovery operations at sea.
Sargasso Sea
   (NASA Thesaurus)
A region in the Atlantic characterized by mixing ocean currents and a lack of winds. Located northeast of the West Indies.
saros
   (NASA SP-7, 1965)
The eclipse cycle of about 18 years, almost the same length as 223 synodical months. See lunar cycle.
At the end of each saros the sun, moon, and line of nodes return to approximately the same relative positions and another series of eclipses begins, closely resembling the series just completed.
SarSat
   (NASA Thesaurus)
The US satellite of the COSPAS-SarSat project for the search and rescue of distressed vehicles, administered by USSR, US, French, and Canadian agencies. Used for Search and Rescue Satellite.
SAS-2
   (Imagine the Universe Dictionary - NASA GSFC)
The second Small Astronomy Satellite: a NASA satellite launched November 1972 with a mission dedicated to gamma-ray astronomy.
SAS-3
   (AS&T Dictionary)
The third Small Astronomy Satellite: a NASA satellite launched May 1975 to determine the location of bright X-ray sources and search for X-ray novae and other transient phenomena.
satellite
   (NASA SP-7, 1965)
1. An attendant body that revolves about another body, the primary; especially in the solar system, a secondary body, or moon, that revolves about a planet. See table XIII for a list of satellites of the solar system.
2. A manmade object that revolves about a spatial body, such as Explorer I orbiting about the earth. See spacecraft, table XIV [not reproduced].
3. Such a body intended and designed for orbiting, as distinguished from a companion body that may incidentally also orbit, as in the observer actually saw the orbiting rocket rather than the satellite.
4. An object not yet placed in orbit, but designed or expected to be launched into an orbit.
satellite atmospheres
   (NASA Thesaurus)
The atmospheres that are found on natural satellites.
satellite communication
   (NASA Thesaurus)
Use of communication satellites, passive reflecting belts of dipoles or needles, or reflecting orbiting balloons to extend the range of radio communication by returning signals to Earth from the orbiting object, with or without amplification.
satellite surfaces
   (NASA Thesaurus)
The crust and soil of natural satellites.
satelloid
   (NASA SP-7, 1965)
A vehicle that revolves about the earth or other body, but at such altitudes as to require sustaining thrust to balance drag.
saturation (chemistry)
   (NASA Thesaurus)
The state of a solution when it holds the maximum equilibrium quantity of dissolved matter at a given temperature.
saturation vapor pressure
   (NASA SP-7, 1965)
1. The vapor pressure of a system, at a given temperature, wherein the vapor of a substance is in equilibrium with a plane surface of the pure liquid or solid phase of that substance; that is, the vapor pressure of a system that has attained saturation but not supersaturation. Compare equilibrium vapor pressure, vapor tension.
The saturation vapor pressure of any pure substance, with respect to a specified parent phase, is an intrinsic property of that substance and is a function of temperature alone (see Clapeyron-Clausius equation).
2. = equilibrium vapor pressure.
saturation-adiabatic lapse rate
   (NASA SP-7, 1965)
A special case of process lapse rate, defined as the rate of decrease of temperature with height of an air parcel lifted in a saturation-adiabatic process through an atmosphere in hydrostatic equilibrium. Also called moist-adiabatic lapse rate.
Owing to the release of latent heat, this lapse rate is less than the dry-adiabatic lapse rate, and the differential equation representing the process must be integrated numerically. Wet-bulb potential temperature is constant with height in an atmosphere with this lapse rate.
Saturn
   (NASA SP-7, 1965)
See planet, table.
Saturn 5 launch vehicles
   (From Stargazers to Starships Glossary - GSFC)
The biggest rocket built to date, weighing 2700 tons fully loaded. It was used to launch NASA's Moon mission and the Skylab space station.
Saturn atmosphere
   (NASA Thesaurus)
The outer shell of gas surrounding the planet Saturn.
Saturn satellites
   (NASA Thesaurus)
The natural satellites of the planet Saturn.
saturnographic
   (NASA SP-7, 1965)
Referring to positions on Saturn measured in latitude from Saturn's equator and in longitude from a reference meridian.
scalar
   (NASA SP-7, 1965)
Any physical quantity whose field can be described by a single numerical value at each point in space.
A scalar quantity is distinguished from a vector quantity by the fact that a scalar quantity possesses only magnitude, whereas a vector quantity possesses both magnitude and direction.
scalar acceleration
   (NASA SP-7, 1965)
The square root of the sum of the squares of three orthogonal components of an acceleration.
scalar product
   (NASA SP-7, 1965)
A scalar equal to the product of the magnitudes of any two vectors and the cosine of the angle theta between their positive directions. Also called dot product, direct product, inner product. See vector product.
For two vectors A and B, the scalar product is most commonly written AdotB, read A dot B, and occasionally as (AB). If the vectors A and B have the components Ax, Bx, and Ay, By, and Az, Bz along rectangular Cartesian, x, y, and z axes, respectively, then

A dot B equals A sub x B sub x plus A sub y B sub y plus A sub z B sub z equals the absolute value of A the absolute value of B cosine theta equals A B cosine theta

If a scalar product is zero, one of the vectors is zero or else the two are perpendicular.
scalar velocity
   (NASA SP-7, 1965)
The square root of the sum of the squares of three orthogonal components of a velocity.
scale effect
   (NASA Thesaurus / NASA SP-7, 1965)
Any variation in the nature of the flow and in the force coefficients associated with a change in value of the Reynolds number, i.e., caused by change is size without change in shape.
scale height
   (NASA Thesaurus / NASA SP-7, 1965)
(symbol h, hs )
A measure of the relationship between density and temperature of any point in an atmosphere; the thickness of a homogeneous atmosphere which would give the observed temperature:

h = kT/mg = R*T/Mg

where k is the Boltzmann constant; T is the absolute temperature; m and M are the mean molecular mass and weight, respectively, of the layer; g is the acceleration of gravity; and R* is the universal gas constant. Compare virtual height.
scale model
   (NASA Thesaurus)
Three-dimensional representations of objects or structures containing all parts in the same proportion as their true size.
scale model
   (NASA SP-7, 1965)
A model of a different size from its prototype and having dimensions in some constant ratio to the dimensions of the prototype, especially such a model of smaller size than its prototype.
scale of 10 counter
   (NASA SP-7, 1965)
= decade counter.
scaler
   (NASA Thesaurus / NASA SP-7, 1965)
A device that produces an output pulse whenever a prescribed number of input pulses have been received. Also called scaling circuit.
The number of input pulses per output pulse of a scaler is termed the scaling factor. A binary scaler is a scaler whose scaling factor is 2. A decade scaler is a scaler whose scaling factor is 10.
scaling circuit
   (NASA SP-7, 1965)
= scaler.
scaling factor
   (NASA SP-7, 1965)
See scalar, note.
scaling laws
   (Plasma Physics and Fusion Energy Glossary)
These are mathematical rules explaining how variation in one quantity affects variations in other quantities. For instance, in a tokamak reactor it's generally believed that energy confinement depends on the size of the device and the strength of the magnetic field, but the precise nature of the dependence is not fully understood, so empirical "scaling laws" are tested to see what the dependence is. Scaling laws are useful for extrapolating from parameter regimes where the mathematical relationships between the various quantities are known, into unexplored regimes.
scanner
   (NASA Thesaurus / NASA SP-7, 1965)
A radar mechanism incorporating a rotatable antenna, or radiator, motor drives, mounting, etc., for directing a searching radar beam through space and imparting target information to an indicator. See parabolic reflector.
scanning
   (NASA Thesaurus / NASA SP-7, 1965)
In radar, the motion of the radar antenna assembly when searching for targets.
Scanning usually follows a systematic pattern involving one or more of the following: (1) In horizontal scanning (or searchlighting), the antenna is continuously rotated in azimuth around the horizon or in a sector (sector scanning); used to generate plan-position-indicator-scope displays. (b) Vertical scanning is accomplished by holding the azimuth constant but varying the elevation angle of the antenna; used in height-finding radars to generate the relative-height-indicator-scope display. (c) For conical scanning, a somewhat offcenter radiating element is rotated while its parabolic reflectors fixed in position so that the radiated beam generates a concially shaped volume with the antenna at the apex; used to determine accurate bearing and elevation angle of targets and employed in automatic tracking radars. (d) In helical scanning (or spiral scanning) the azimuth and elevation angle of the antenna are constantly varied so that at a given distance from the radar the radiated beam generates the surface of a hemisphere; used for radio direction finding, in certain types of search radars, and in tracking radars to search areas for targets.
scanning electron microscopy
   (NASA Thesaurus)
A type of electron microscopy in which a beam of electrons, a few hundred angstroms in diameter, systematically sweeps over the specimen. The intensity of secondary electrons generated at the point of impact of the beam on the specimen is measureed and the resulting signal is fed into a cathode-ray-tube display which is scanned in synchronism with the scanning of the specimen.
scaphandre
   (NASA SP-7, 1965)
= full pressure suit.
scarf joints
   (NASA Thesaurus)
A joint in which the overlapping parts are tapered to form a continuous length, with no increase in dimension at the joint.
scarp
   (Galileo Project Glossary - JPL)
A line of cliffs produced by faulting or erosion; a relatively straight, cliff-like face or slope of considerable linear extent, breaking the general continuity of the land by separating surfaces lying at different levels.
SCATHA satellite
   (NASA Thesaurus)
Satellite for investigating spacecraft charging at high altitudes. A joint NASA-Air Force venture. Used for P78-2 satellite.
scatter
   (NASA SP-7, 1965)
1. = scattering.
2. The relative dispersion of points on a graph, especially with respect to a mean value, or any curve used to represent the points. See dispersion.
3. To accomplish scattering.
scatter angle
   (NASA SP-7, 1965)
The angle between any given ray of scattered radiation and the incident ray. See relative scatter intensity, scattering.
Convention varies as to whether this angle is measured with respect to the direction in which the incident radiation was advancing or with respect to the direction from scatterer to radiation source.
scatter communication
   (NASA SP-7, 1965)
See scatter propagation, note.
scatter plates (optics)
   (NASA Thesaurus)
Holograms of diffusing screens for scattering incident light by the process of diffraction.
scatter propagation
   (NASA Thesaurus / NASA SP-7, 1965)
Specifically, the long-range propagation of radio signals by scattering due to index of refraction inhomogeneities in the lower atmosphere. Also called tropospheric propagation.
Recognition of this process and the development of specialized equipment (basically, more powerful transmitters and sensitive receivers) has greatly increased the range of VHF and UHF communication. The over-all technique is known as scatter communication.
scattered power
   (NASA SP-7, 1965)
= received power.
scatterer
   (NASA SP-7, 1965)
= scattering particle.
scattering
   (NASA Thesaurus / NASA SP-7, 1965)
The process by which small particles suspended in a medium of a different index of refraction diffuse a portion of the incident radiation in all directions. In scattering, no energy transformation results, only a change in the spatial distribution of the radiation. Also called scatter.
Along with absorption, scattering is a major cause of the attenuation of radiation by the atmosphere. Scattering varies as a function of the ratio of the particle diameter to the wavelength of the radiation. When this ratio is less than about one-tenth, Rayleigh scattering occurs in which the scattering coefficient varies inversely as the fourth power of the wavelength. At larger values of the ratio of particle diameter to wavelength, the scattering varies in a complex fashion described by the Mie theory; at a ratio of the order of 10, the laws of geometric optics begin to apply.
scattering area coefficient
   (NASA SP-7, 1965)
The dimensionless ratio of the scattering cross section to the geometric cross section of a scattering particle. Also called scattering area ratio.
scattering area ratio
   (NASA SP-7, 1965)
= scattering area coefficient.
scattering coefficient
   (NASA Thesaurus / NASA SP-7, 1965)
A measure of the attenuation due to scattering of radiation as it traverses a medium containing scattering particles. Also called total scattering coefficient.
scattering cross sections
   (NASA Thesaurus / NASA SP-7, 1965)
The hypothetical areas normal to the incident radiation that would geometrically intercept the total amount of radiation actually scattered by a scattering particle. They are also defined, equivalently, as the cross-section areas of an isotropic scatterer (a sphere) which would scatter the same amount of radiation as the actual amount. Also called extinction cross section, effective area.
scattering function
   (NASA Thesaurus / NASA SP-7, 1965)
The intensity of scattered radiation in a given direction per lumen of flux incident upon the scattering material.
scattering gage
   (NASA SP-7, 1965)
= scattering-type pressure gage.
scattering loss
   (NASA SP-7, 1965)
That part of the transmission loss which is due to scattering within the medium or due to roughness of the reflecting surface.
scattering particle
   (NASA SP-7, 1965)
The small particles responsible for scattering.
scattering power
   (NASA SP-7, 1965)
In radar terminology, the ratio of the total power scattered by a target to the power in the incident wave, independent of the direction of scattering. The scattering power measures the loss of energy by absorption in the scatterers. Also called total scattering cross section. Compare radar reflectivity.
scattering-type pressure gage
   (NASA SP-7, 1965)
An ionization gage in which measurement is made of the electrons scattered by collision of the gas molecules with the electrons from a p-particle emitter.
SCET
   (Space Flight Glossary - JPL)
Spacecraft Event Time, equal to ERT minus OWLT.
Schach effect
   (NASA Thesaurus)
When a slowly or nonrotating satellite is heated on its sunward side, the photons of thermal radiation carry away more momentum from the hot sunward side than the cold shadowed side, thereby giving the satellite a certain net acceleration in the direction away from the sun. This effect was discovered by Milton Schach in the course of an investigation of unknown perturbations in the LAGEOS satellite.
schist
   (NASA Thesaurus)
A strongly foliated crystalline rock formed by dynamic metamorphism which can be readily split into thin flakes or slabs due to the well developed parallelism of more then 50% of the minerals present.
schlieren
   (NASA SP-7, 1965)
(German, streaks, striae).
1. Regions of different density in a fluid, especially as shown by special apparatus.
2. Pertaining to a method or apparatus for visualizing or photographing regions of varying density in a field of flow. See schlieren photography, scintillation.
Used in compounds, such as schlieren lens, schlieren method, schlieren photograph, etc.
schlieren method
   (Plasma Physics and Fusion Energy Glossary)
An optical technique that detects density gradients occuring in a fluid flow. In its simplest form, light from a slit is collimated by a lens and focused onto a knife edge by a second lens; the flow pattern is placed between the two lenses, and the resulting diffraction pattern is observed on a screen or photographic film placed behind the knife edge.
schlieren method
   (NASA SP-7, 1965)
See schlieren.
schlieren photography
   (NASA Thesaurus / NASA SP-7, 1965)
A method of photography for flow patterns that take advantage of the fact that light passing through a density gradient in a gas is refracted as though it were passing through a prism. Compare shadowgraph.
Schneider index
   (NASA SP-7, 1965)
A composite weighted index of pulse and blood-pressure response to exercise, utilized as a test of physical efficiency.
Schuler pendulum
   (NASA SP-7, 1965)
A hypothetical pendulum with a period of 84 minutes.
A simulated Schuler pendulum carried in a vehicle moving in the earth's gravitational field would always indicate the true vertical.
Schuler tuning
   (NASA Thesaurus / NASA SP-7, 1965)
Adjusting a system performing the function of a pendulum so that is has a period of 84 minutes. See Schuler pendulum.
Schumann-Runge bands
   (NASA SP-7, 1965)
See absorption band.
Schumann-Runge continuum
   (NASA SP-7, 1965)
See absorption band.
Schwarzschild radius
   (High Energy Astrophysics Dictionary- GSFC)
The radius r of the event horizon for a Schwarzschild black hole.
scientific notation
   (High Energy Astrophysics Dictionary- GSFC)
A compact format for writing very large or very small numbers, most often used in scientific fields. The notation separates a number into two parts: a decimal fraction, usually between 1 and 10, and a power of ten.
scintillating counter
   (NASA SP-7, 1965)
= scintillation counter.
scintillation
   (NASA Thesaurus / NASA SP-7, 1965)
1. Generic term for rapid variations in apparent position, brightness, or color of a distant luminous object viewed through the atmosphere.
If the object lies outside the earth's atmosphere, as in the case of stars and planets, the phenomenon is termed astronomical scintillation; if the luminous source lies within the atmosphere, the phenomenon is termed terrestrial scintillation. As one of the three principal factors governing astronomical seeing, scintillation is defined as variations in luminance only. It is clearly established that almost all scintillation effects are caused by anomalous refraction occurring in rather small parcels or strata of air, schlieren, whose temperatures and hence densities differ slightly from those of their surroundings. Normal wind motions transporting such schlieren across the observer's line of sight produce the irregular fluctuations characteristic of scintillation. Scintillation effects are always much more pronounced near the horizon than near the zenith. Parcels of the order of only centimeters to decimeters are believed to produce most of the scintillatory irregularities in the atmosphere.
2. A flash of light produced in a phosphor by an ionizing event. See scintillation counter. 3. On a radar display, a rapid apparent displacement of the target from its mean position. Also called target glint or wander.
This includes but is not limited to shift of effective reflection point on the target.
scintillation counter
   (NASA Thesaurus / NASA SP-7, 1965)
The combination of phosphor, photomultiplier tube, and associated circuits for counting scintillations, sense 2. Also called scintillating counter.
scintillation meter
   (NASA SP-7, 1965)
= scintillometer.
scintillometer
   (NASA SP-7, 1965)
A type of photoelectric photometer used in a method of determining high altitude winds on the assumption that stellar scintillation is caused by atmospheric inhomogeneities ( schlieren) being carried along by the wind near tropopause level. Also called scintillation meter.
Scl, Scul
   (NASA SP-7, 1965)
International Astronomical Union abbreviations for Sculptor. See constellation.
SCLK
   (Space Flight Glossary - JPL)
Spacecraft Clock Time, a counter onboard a spacecraft.
Sco, Scor
   (NASA SP-7, 1965)
International Astronomical Union abbreviations for Scorpius. See constellation.
scope
   (NASA SP-7, 1965)
The general abbreviation for an instrument of viewing, such as telescope, microscope, and oscilloscope. In radar installations, the cathode-ray oscilloscope indicators are commonly referred to as scopes or radarscopes.
Because of possible ambiguity this term should be avoided in formal reports.
Scor
   (NASA SP-7, 1965)
International Astronomical Union abbreviation for Scorpius. See constellation.
Scorpius
   (NASA SP-7, 1965)
(abbr Sco, Scor)
See constellation.
scotopic vision
   (NASA SP-7, 1965)
Vision associated with levels of illumination below approximately 0.01 foot-lambert, effective primarily in the detection of movement and low luminous intensities. Compare photopic vision. Also called parafoveal vision.
Scotopic vision is associated with rod function.
screaming
   (NASA SP-7, 1965)
A form of combustion instability, especially in a liquid propellant rocket engine, of relatively high frequency and characterized by a high-pitched noise.
screech tones
   (NASA Thesaurus)
Discrete acoustic tones produced by imperfectly expanded supersonic jets. The phenomenon is a result of a resonant feedback condition involving downstream traveling shear-layer disturbances and upstream traveling acoustic waves.
screeching
   (NASA SP-7, 1965)
A form of combustion instability, especially in an afterburner, of relatively high frequency and characterized by a harsh, shrill noise.
screen
   (NASA SP-7, 1965)
1. A device to shield or separate one part of an apparatus from other parts, or to separate the effects of one part on others.
2. A surface on which images are displayed, as the face of a cathode-ray tube.
screw pinch
   (NASA Thesaurus)
A cylindrical plasma equilibrium in which the axial and azimuthal components of the vacuum field are of the same size.
scrub
   (NASA SP-7, 1965)
To cancel a scheduled firing, either before or during countdown.
scrubbers
   (NASA Thesaurus)
Apparatus used in sampling and in gas cleaning in which the gas is passed through a space containing wetted "packing" or spray.
Sct, Scut
   (NASA SP-7, 1965)
International Astronomical Union abbreviations for Scutum. See constellation.
Scul
   (NASA SP-7, 1965)
International Astronomical Union abbreviations for Sculptor. See constellation.
Sculptor
   (NASA SP-7, 1965)
(abbr Scl, Scul)
See constellation.
Scutum
   (NASA SP-7, 1965)
(abbr Sct, Scut)
See constellation.
sea breeze
   (NASA Thesaurus)
A coastal, local wind that blows from sea to land caused by temperature differences when the sea surface is colder than the adjacent land.
sea clutter
   (NASA SP-7, 1965)
See ground return.
sea floor spreading
   (NASA Thesaurus)
A hypothesis that the oceanic crust is increasing by convective upwelling of magma along the mid-ocean ridges or world rift system, and by a moving-away of the new material at a rate of one to ten centimeters per year. This movement provides the source of dynamic thrust in the hypothesis of plate tectonics.
sea keeping
   (NASA Thesaurus)
Maintaining the stability of a surface vessel in linear response to wave height, pitch, heave, center of gravity, and bow acceleration.
sea law
   (NASA Thesaurus)
United Nations declaration regarding rights to minerals and other marine resources.
sea level
   (NASA Thesaurus)
The level of the surface of the ocean; especially, the mean level halfway between high and low tide used as a standard in reckoning land elevation or sea depths.
sea level
   (NASA SP-7, 1965)
= mean sea level.
sea return
   (NASA SP-7, 1965)
See ground return.
sea-level pressure
   (NASA SP-7, 1965)
The atmospheric pressure at mean sea level, either directly measured or, most commonly, empirically determined from the observed station pressure.
sealed cabin
   (NASA SP-7, 1965)
The occupied space of an aircraft or spacecraft characterized by walls which do not allow any gaseous exchange between the inner atmosphere and its surrounding atmosphere and containing its own mechanisms for maintenance of the inside atmosphere.
seamounts
   (NASA Thesaurus)
Elevations of the ocean floor rising to about 3000-1000 feet or more with the summit about 1000-6000 feet below sea level.
search radar
   (NASA SP-7, 1965)
A radar designed for the approximate location of (usually airborne) objects. Search radar beams are usually wide, wider in the vertical than in the horizontal, making it possible to scan large volumes of space quickly. Compare tracking radar.
searchlighting
   (NASA SP-7, 1965)
Horizontal scanning, in which the antenna beam is continuously rotated in azimuth.
seas
   (NASA Thesaurus)
Inland bodies of salt water or geographic divisions of oceans or ocean areas of wave generation.
seat belt
   (NASA Thesaurus)
Safety belts that fasten across the lap.
seat belt
   (NASA SP-7, 1965)
= lap belt.
seat-to-head acceleration
   (NASA SP-7, 1965)
See physiological acceleration.
sec
   (Space Flight Glossary - JPL)
Second.
second
   (NASA SP-7, 1965)
(abbr s)
See
The unit of time, the second, was defined originally as the fraction 1/86 400 of the mean solar day. The exact definition of the "mean solar day" was left to astronomers, but their measurements have shown that on account of irregularities in the rotation of the Earth, the mean solar day does not guarantee the desired accuracy. In order to define the unit of time more precisely, the 11th CGPM (1960) adopted a definition given by the International Astronomical Union which was based on the tropical year [see ephemeris second]. Experimental work had, however, already shown that an atomic standard of time-interval, based on a transition between two energy levels of an atom or a molecule, could be realized and reproduced much more accurately. Considering that a very precise definition of the unit of time of the International System, the second, is indispensable for the needs of advanced metrology, the 13th CGPM (1967) decided to replaced the defintion of the second by the following:


The second is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium-133 atom (13th CGPM (1967), Resolution 1).

The previous is an excerpt (with the exception of the reference to "ephemeris second") from WWW version of the National Institute of Standards and Technology: Physics Laboratory's International System of Units (SI)

second law of thermodynamics
   (NASA SP-7, 1965)
An inequality asserting that it is impossible to transfer heat from a colder to a warmer system without the occurrence of other simultaneous changes in the two systems or in the environment.
It follows from this law that during an adiabatic process, entropy cannot decrease. For reversible adiabatic processes entropy remains constant, and for irreversible adiabatic processes it increases. Another equivalent formulation of the law is that it is impossible to convert the heat of a system into work without the occurrence of other simultaneous changes in the system or its environment. This version, which requires an engine to have a cold source as well as a heat source, is particularly useful in engineering applications. See first law of thermodynamics.
second stability region
   (Plasma Physics and Fusion Energy Glossary)
A high pressure region where the plasma becomes stable to the pressure-gradient-driven ballooning ballooning instability. The plasma is stable in the limit of small pressure gradients, becomes unstable at some intermediate pressure, and then becomes stable again at still higher pressures. Tokamaks operating in the second-stability region would be more attractive because the higher pressures (beta) would provide more fusion reactivity per unit volume of plasma, allowing smaller reactors to be built.
secondary
   (NASA SP-7, 1965)
1. = secondary great circle.
2. A celestial body revolving around another body, its primary.
3. A particle emitted in secondary emission.
secondary circle
   (NASA SP-7, 1965)
= secondary great circle.
secondary cosmic radiation
   (NASA SP-7, 1965)
= secondary cosmic ray.
secondary cosmic rays
   (NASA Thesaurus / NASA SP-7, 1965)
Secondary emission in the atmosphere stimulated by primary cosmic rays. See air shower.
secondary electron emission
   (NASA SP-7, 1965)
The release of electrons from a surface which is bombarded by energetic electrons.
The yield or ratio of secondary to primary electrons is a function of the primary electron energy.
secondary emission
   (NASA Thesaurus / NASA SP-7, 1965)
Emission of subatomic particles or photons stimulated by primary radiation; for example, cosmic rays impinging on other particles and causing them, by disruption of their electron configurations or even of their nuclei, to emit particles and photons or both in turn.
secondary great circle
   (NASA SP-7, 1965)
A great circle perpendicular to a primary great circle, as a meridian. Also called secondary circle, secondary.
secondary instrument
   (NASA SP-7, 1965)
An instrument whose calibration is determined by comparison with an absolute instrument.
secondary ion mass spectrometry
   (NASA Thesaurus)
Mass spectrometry performed on ions sputtered from a sample by a primary ion beam.
secondary radar
   (NASA Thesaurus)
A radar technique or mode of operation in which the return signals are obtained from beacons, transponders, or repeaters carried by the targets, contrasted with primary radar in which the return signals are obtained by reflection from the targets.
secondary radar
   (NASA SP-7, 1965)
See radar, note.
secondary radiation
   (NASA SP-7, 1965)
Electromagnetic or particulate radiation resulting from absorption of other radiation in matter.
secondary scattering
   (NASA SP-7, 1965)
See multiple scattering, scattering.
Secor (abbr)
   (NASA SP-7, 1965)
= sequential collation of range.
Secor/DME
   (NASA SP-7, 1965)
(Sequential collation of range/distance measuring equipment). A distance measuring system used in rocket tracking.
section
   (NASA SP-7, 1965)
One of the cross-section parts that a rocket vehicle is divided into, each adjoining another at one or both of its end. Usually described by a designating word, as in nose section, aft section, center section, tail section, thrust section, tank section , etc.
sectionalized vertical antenna
   (NASA SP-7, 1965)
A vertical antenna which is insulated at one or more points along its length. The insertion of suitable reactances or applications of a driving voltage across the insulated points results in a modified current distribution giving a more desired radiation pattern in the vertical plane.
sector scanning
   (NASA SP-7, 1965)
See scanning.
secular
   (NASA SP-7, 1965)
Pertaining to long periods of time on the order of a century, as secular perturbations, secular terms.
secular perturbations
   (NASA SP-7, 1965)
Changes in the orbit of a planet or satellite that operate in extremely long cycles; long term perturbations.
secular terms
   (NASA SP-7, 1965)
In the mathematical expression of an orbit, terms for very long period perturbations, in contrast to periodic terms , terms of short period.
sedimentary rocks
   (NASA Thesaurus)
Rocks resulting from the consolidation of loose sediments that have accumulated in layers, e.g., clastic rocks (such as fragments of older rocks transported from their source and deposited in water or from air or ice. Sedimentary rocks constitute one of the three main classes into which rocks are divided, the others being igneous rocks and metamorphic rocks.
sediments
   (NASA Thesaurus)
Solid fragmental materials that originate from weathering of rocks and are transported or deposited by air, water, or ice, or that accumulate by other natural agents, such as chemical precipitation from solution or secretion by organisms, and that form in layers on the Earth's surface at ordinary temperatures in a loose, unconsolidated form; e.g., sand, gravel, silt, mud, till, loess, and alluvium.
SEDR
   (Space Flight Glossary - JPL)
Supplementary Experiment Data Record.
Seebeck effect
   (NASA Thesaurus / NASA SP-7, 1965)
The establishment of an electric potential difference tending to produce a flow of current in a circuit of two dissimilar metals the junctions of which are at different temperatures.
seeding
   (NASA SP-7, 1965)
1. The introduction of atoms, such as sodium, with a low ionization potential into a hot gas for the purpose of increasing the electrical conductivity.
2. = cloud seeding.
seeing
   (NASA SP-7, 1965)
A blanket term long used by astronomers for the disturbing effects produced by the atmosphere upon the image quality of an observed celestial body. Also called astronomical seeing.
Recent studies show that seeing is a combination of three principal and distinct effects that the human eye is not capable of distinguishing: (a) scintillation, i.e., fluctuations in brightness; (b) transverse displacements of the image; and (c) variations of the radius of curvature of the wavefront rendering the image in an out of focus.
SEF
   (Space Flight Glossary - JPL)
Spacecraft event file.
segmented mirrors
   (NASA Thesaurus)
Telescope mirrors made up of many small, thin, glass segments. Motorized controllers keep the segments optically aligned to form a single large mirror.
SEGS
   (Space Flight Glossary - JPL)
Sequence of Events Generation Subsystem.
seismic mass
   (NASA SP-7, 1965)
The element in an accelerometer which is intended to serve as the force-summing member for applied accelerations, gravitational forces, or both.
seismic waves
   (NASA Thesaurus)
The disturbance of earth tremors produced by a mechanical disturbance on the surface or underground. Used for electroseismic effect.
seismocardiography
   (NASA Thesaurus)
The measurement of the high frequency vibrations of the heart.
seismology
   (NASA Thesaurus)
The study of earthquakes, by extension, the structure of the interior of the Earth via both natural and artificially generated seismic signals.
selective absorption
   (NASA SP-7, 1965)
Absorption which varies with the wavelength of radiation incident upon the absorbing substance. See absorption spectrum.
A substance which absorbs in such fashion is called a selective absorber and is to be contrasted with an ideal blackbody, white body, or gray body. In reality, all substances are selective absorbers when due regard is paid to their interaction with all wavelengths of the complete electromagnetic spectrum.
selective scattering
   (NASA SP-7, 1965)
Scattering which varies with the wavelengths of radiation incident upon the scattering particles.
In general, the largest and most complex degree of selectivity is found for wavelengths nearly equal to the diameter of the scattering particles.
selective surfaces
   (NASA Thesaurus)
Surfaces, often coated, for which the spectral optical properties, such as reflectance, absorptance, emittance, or transmittance vary significantly with wavelength. Such properties are of interest in solar energy applications. Used for solar selective coatings.
selectivity
   (NASA SP-7, 1965)
The degree of falling off in response of a resonant device with departure from resonance.
selenocentric
   (NASA SP-7, 1965)
Relating to the center of the moon; referring to the moon as a center.
selenographic
   (NASA SP-7, 1965)
1. Of or pertaining to the physical geography of the moon.
2. Specifically, referring to positions on the moon measured in latitude from the moon's equator and in longitude from a reference meridian.
selenoid
   (NASA SP-7, 1965)
A satellite of the earth's moon. (No such satellites are known).
selenology
   (NASA Thesaurus / NASA SP-7, 1965)
That branch of astronomy that treats of the moon, its magnitude, motion, constitution, and the like. Selene is Greek for moon.
self adaptive control systems
   (NASA Thesaurus)
Particular types of stability augmentation systems which change the responses of given control inputs by constantly sampling responses and adjusting their gain, rather than having fixed or selective gain systems.
self diffusion (solid state)
   (NASA Thesaurus)
The spontaneous movement of an atom to a new site in a crystal of its own species.
self tests
   (NASA Thesaurus)
Programmed functions performed by a machine, either automatically at start-up or on user demand, that test the working order of the machine. In particular, programs stored in read-only memory that test the integrity of a machine's integrated circuits and the connections between the circuits and the devices they control.
self-adaptive control system
   (NASA SP-7, 1965)
A particular type of stability augmentation system which changes the response of a given control input by constantly sampling response and adjusting its gain, rather than having a fixed or selective gain system.
self-balancing potentiometer
   (NASA SP-7, 1965)
See potentiometer.
self-excited vibration
   (NASA SP-7, 1965)
= self-induced vibration.
self-induced vibration
   (NASA SP-7, 1965)
Vibration of a mechanical system resulting from conversion, within the system, of nonoscillatory excitation to oscillatory excitation. Also called self-excited vibration.
self-information
   (NASA SP-7, 1965)
= information content.
selsyn
   (NASA SP-7, 1965)
(A trade name, from self-synchronous; often capitalized). An electrical remote indicating instrument operating on direct current, in which the angular position of the transmitter shaft, carrying a contact arm moving on a resistance strip, controls the pointer on the indicator dial.
semiactive homing guidance
   (NASA SP-7, 1965)
Guidance in which a craft or vehicle is directed toward a destination by means of information received from the destination in response to transmissions from a source other than the craft.
In active homing guidance the information received is in response to transmissions from the craft. In passive homing guidance natural radiations from the destination are utilized.
semiactive tracking system
   (NASA SP-7, 1965)
A trajectory measuring system which tracks a signal source normally aboard the target for other purposes, or a system that illuminates the target by use of a ground transmitter but requires no special electronics on board the missile, e.g., telemetry elsse, Dovap elsse, Cotat, Cotar, VHF/ ADF, pulse radar (skin track).
semicircular canals
   (NASA Thesaurus / NASA SP-7, 1965)
Structures of the inner ear, the primary function of which is to register movement of the body in space. They respond to change in the rate of movement.
semiconductor
   (NASA SP-7, 1965)
An electronic conductor, with resistivity in the range between metals and insulators, in which the electrical charge carrier concentration increases with increasing temperature over some temperature range. Certain semiconductors possess two types of carriers, namely, negative electrons and positive holes.
semiconductor device
   (NASA Thesaurus / NASA SP-7, 1965)
An electron device in which the characteristic distinguishing electronic conduction takes place within a semiconductor.
semiconductor diodes
   (NASA Thesaurus)
Two-electrode semiconductor devices utilizing the rectifying properties of junctions or point contacts.
semiconductors (materials)
   (NASA Thesaurus)
Electronic conductors, with resistivity in the range between metals and insulators, in which the electrical charge carrier concentration increases with increasing temperature over some temperature range. Certain semiconductors possess two types of carriers, namely, negative electrons and positive holes.
semidiameter
   (NASA SP-7, 1965)
1. The radius of a closed figure.
2. Half the angle at the observer subtended by the visible disk of a celestial body.
semidiameter correction
   (NASA SP-7, 1965)
A correction due to semidiameter, particularly that sextant altitude correction resulting from observation of the upper or lower limb of a celestial body, rather than the center of that body.
semidiurnal
   (NASA SP-7, 1965)
Having a period of, occurring in, or related to approximately half a day.
semimajor axis
   (IMO Meteor Glossary)
Abbr. a. Half the length of the major axis of an ellipse or other geometric figure; a standard element used to describe an elliptical orbit.
semimajor axis
   (NASA SP-7, 1965)
(symbol a )
One-half the longest diameter of an ellipse.
semiminor axis
   (NASA SP-7, 1965)
(symbol b )
One-half the shortest diameter of an ellipse.
semimonocoque
   (NASA SP-7, 1965)
A structural concept in which longitudinal members as well as formers reinforce the skin and help carry the stresses. Compare with monocoque.
semitransparent photocathode
   (NASA SP-7, 1965)
A photocathode in which radiant flux incident on one side produces photoelectric emission from the opposite side. See phototube.
sensation level
   (NASA SP-7, 1965)
The level of psychophysiologic stimulation above the threshold.
sense antenna
   (NASA SP-7, 1965)
An antenna used to resolve a 180 degrees ambiguity in a directional antenna.
sense-reversing reflectivity
   (NASA SP-7, 1965)
The characteristic of a reflector that reverses the sense of a circularly polarized incident ray. See polarization.
For example, a perfect corner reflector is invisible to a circularly polarized radar because it reverses the sense.
sensibility
   (NASA SP-7, 1965)
In measurements, the smallest change that is reliably detectable.
sensible atmosphere
   (NASA SP-7, 1965)
That part of the atmosphere that offers resistance to a body passing through it.
sensible horizon
   (NASA SP-7, 1965)
See horizon, note.
sensible temperature
   (NASA SP-7, 1965)
The temperature at which average indoor air of moderate humidity would induce, in a lightly clothed person, the same sensation of comfort as that induced by the actual environment. Compare effective temperature.
Sensible temperature depends on the air temperature; radiation from the sun, sky, and surrounding objects; relative humidity; and air motion. The wet-bulb temperature is often taken as an approximate measure.
sensing element
   (NASA SP-7, 1965)
= sensor.
sensitivity
   (NASA Thesaurus)
Response of a mathematical model to variations of the input parameters. Used for insensitivity and sensibility.
sensitivity
   (Imagine the Universe Dictionary - NASA GSFC)
A measure of how bright objects need to be in order for that telescope to detect these objects. A highly sensitive telescope can detect dim objects, while a telescope with low sensitivity can detect only bright ones.
sensitivity
   (NASA SP-7, 1965)
1. The ability of electronic equipment to amplify a signal, measured by the minimum strength of signal input capable of causing a desired value of output. The lower the input signal for a given output, the higher the sensitivity.
2. In measurements, the derivative representing the change in instrument indication produced by a change in the variable being measured.
sensitometry
   (NASA Thesaurus / NASA SP-7, 1965)
The measurement of the light response characteristics of photographic film under specified conditions of exposure and development.
sensor
   (NASA Thesaurus)
Devices designed to respond to physical stimuli (as temperature, illumination, and motion) and transmit a resulting signal for interpretation, or measurement, or for operating a control. Used for pickoffs and pickups.
sensor
   (NASA SP-7, 1965)
1. The component of an instrument that converts an input signal into a quantity which is measured by another part of the instrument. Also called sensing element.
2. The nerve endings or sense organs which receive information from the environment, from the organism, or from both.
SEOCS (satellite)
   (NASA Thesaurus)
An ESA meteorological satellite designed for sun-Earth observation and climatology.
SEPAC (payload)
   (NASA Thesaurus)
Space experiment particle accelerators. A Spacelab 1 payload that experiments on the Earth's ionosphere and magnetosphere. Used for Space Exper with Particle Accelerators.
separation
   (NASA SP-7, 1965)
1. The action of a fallaway section or companion body as it casts off from the remaining body of a vehicle, or the action of the remaining body as it leaves a fallaway section behind it.
2. The moment of this action.
separation velocity
   (NASA SP-7, 1965)
The velocity at which a space vehicle is moving when some part or section is separated from it; specifically, the velocity of a space probe or satellite at the time of separation from the launch vehicle.
September equinox
   (NASA SP-7, 1965)
= autumnal equinox.
sequencer
   (NASA SP-7, 1965)
A mechanical or electronic device that may be set to initiate a series of events and to make the events follow in a given sequence. See program.
sequential collation of range
   (NASA SP-7, 1965)
(abbr Secor) A spherical, long-baseline, phase-comparison trajectory measuring system utilizing three or more ground stations, time sharing a single transponder, to provide nonambiguous range measurements to determine the instantaneous position of a vehicle in flight.
sequential control
   (NASA Thesaurus / NASA SP-7, 1965)
Control by completion of a series of one or more events.
Ser, Serp
   (NASA SP-7, 1965)
International Astronomical Union abbreviations for Serpens (Cap. and Caud.). See constellation.
series expansion
   (NASA Thesaurus)
In mathematics, a divergent series of terms the sum of which is asymptotic or ascending.
Serpens
   (NASA SP-7, 1965)
(Cap. and Caud.) (abbr Ser, Serp)
See constellation.
Service Module (ISS)
   (NASA Thesaurus)
Primary Russian component of the International Space Station providing an early station living quarters and life support system functions to all early elements. Also provides propulsive attitude control and reboost capability for the early station.
servo
   (NASA SP-7, 1965)
1. = servomechanism.
2 Pertaining to or incorporating a servomechanism.
servomechanism
   (NASA Thesaurus / NASA SP-7, 1965)
A control system incorporating feedback in which one or more of the system signals represent mechanical motion.
It should be noted that servomechanism and regulator are not mutually exclusive terms; their application to a particular system will depend on the method of operation of that system.
set
   (NASA SP-7, 1965)
1. To place a storage device in a prescribed state.
2. To place a binary cell in the one state.
sewers
   (NASA Thesaurus)
Networks of pipelines for the transportation of metabolic and/or industrial wastes for disposal.
Sex, Sext
   (NASA SP-7, 1965)
International Astronomical Union abbreviations for Sextans. See constellation.
sexidecimal notation
   (NASA SP-7, 1965)
A positional notation based on the integer sixteen.
Sext
   (NASA SP-7, 1965)
International Astronomical Union abbreviation for Sextans. See constellation.
Sextans
   (NASA SP-7, 1965)
(abbr Sex, Sext)
See constellation.
sextant
   (NASA Thesaurus / NASA SP-7, 1965)
A double-reflecting instrument for measuring angles, primarily altitudes of celestial bodies.
As originally used, the term applied only to instruments having an arc of 60 degrees, a sixth of a circle, from which the instrument derived its name. Such an instrument had a range of 120 degrees. In modern practice the term applies to a similar instrument, regardless of its range, very few modern instruments being sextants in the original sense.
sextant altitude
   (NASA SP-7, 1965)
The altitude of a celestial body as actually measured by a sextant. See altitude difference.
Seyfert galaxies
   (High Energy Astrophysics Dictionary- GSFC)
A spiral galaxy whose nucleus shows bright emission lines; one of a class of galaxies first described by C. Seyfert.
sferics
   (NASA SP-7, 1965)
1. (Also spelled spherics ). The study of atmospherics, especially from a meteorological point of view. This involves techniques of locating and tracking atmospherics sources and evaluating received signals (waveform, frequency, etc.) in terms of source.
2. = atmospherics.
sferics fix
   (NASA SP-7, 1965)
The estimated location of a source of atmospherics, presumably a lightning discharge.
sferics observation
   (NASA SP-7, 1965)
An evaluation, from one or more sferics receivers, of the location of weather conditions with which lightning is associated.
Such observations are more commonly obtained from networks of two or three widely spaced stations. Simultaneous observations of the azimuth of the discharge are made at all stations and the location of the storm is determined by triangulation.
sferics receiver
   (NASA SP-7, 1965)
An instrument which measures, electronically, the direction of arrival, intensity, and rate of occurrence of atmospherics. In its simplest form the instrument consists of two orthogonally crossed antennas. Their output signals are connected to an oscillograph so that one loop measures the north-south component whereas the other measures the east-west component. These are combined vertically to give the azimuth. Also called lightning recorder.
Sge, Sgte
   (NASA SP-7, 1965)
International Astronomical Union abbreviation for Sagitta. See constellation.
SGR
   (NASA Thesaurus)
[astronomy] See soft gamma repeaters
Sgr, Sgtr
   (NASA SP-7, 1965)
International Astronomical Union abbreviation for Sagittarius. See constellation.
Sgte
   (NASA SP-7, 1965)
International Astronomical Union abbreviation for Sagitta. See constellation.
Sgtr
   (NASA SP-7, 1965)
International Astronomical Union abbreviation for Sagittarius. See constellation.
shaded relief
   (Global Land Information System Glossary - USGS)
Shading added to an image that makes the image appear to have three dimensional aspects. This type of enhancement is commonly done to satellite images and thematic maps utilizing digital topographic data to provide the appearance of terrain relief within the image.
shadow
   (NASA Thesaurus / NASA SP-7, 1965)
Darkness in a region, caused by an obstruction between the source of light and the region.
By extension, the term is applied to a similar condition when any form of radiant energy is cut off by an obstruction, as a radar shadow. The darkest part of a shadow in which light is completely cut off is called the umbra; a lighter part surrounding the umbra, in which the light is only partly cut off, is called the penumbra.
shadow shield
   (NASA SP-7, 1965)
A shield that is interposed between a radiation source and a specific area to be protected.
Useful in space, a shadow shield is less effective in the earth's atmosphere because air scattering deflects radiation around it.
shadowgraph
   (NASA SP-7, 1965)
1. A picture or image in which steep density gradients in the flow about a body are made visible, the body itself being presented in silhouette.
2. The optical method or technique by which this is done. A shadowgraph differs from a schlieren photograph in that the schlieren method depends on the first derivative of the refractive index while the shadow method depends on the second derivative. Interference measurements give the refractive index directly.
shadowgraph photography
   (NASA Thesaurus)
Photography in which steep density gradients in the flow about a body are made visible, the body itself being presented in silhouette. Used for shadowgraphs and spark shadowgraph photography.
shake-table test
   (NASA SP-7, 1965)
A laboratory test for vibration tolerance, in which the device to be tested is place in a vibrator.
shaker
   (NASA SP-7, 1965)
An electromagnetic device capable of imparting known vibratory acceleration to a given object.
shales
   (NASA Thesaurus)
Fine grained detrital sedimentary rocks, formed by the consolidation (especially by compression) of clay, silt, or mud. They are characterized by finely laminated structures, which impart a fissility approximately parallel to the bedding, along which rocks break readily into thin layers and are commonly most conspicuous on weathered surfaces. They are characterized by an appreciable content of clay minerals and detrital quartz; thinly laminated or fissile claystones, siltstones, or mudstones.
shape control
   (NASA Thesaurus)
The control of large flexible platforms in orbit by means of actuators strategically located.
shape memory alloys
   (NASA Thesaurus)
Martensitic alloys (titanium-nickel) which exhibit shape recovery characteristics by stress-induced transformation and reorientation. Reverse transformation during heating restores the original grain structure of the high temperature phase.
shaped charges
   (NASA Thesaurus)
An explosive device configured so that its energy can be controlled in one direction.
shaped-beam antenna
   (NASA SP-7, 1965)
A unidirectional antenna whose major lobe differs materially from that obtainable from an aperture of uniform phase. Also called phase-shaped antenna.
shatter cones
   (NASA Thesaurus)
Distinctively striated conical rock fragments along which fracturing has occurred, ranging in length from less than a centimeter to several meters, and generally found in nested or composite groups in rocks of cryptoexplosion structures and believed to be formed by shock waves generated by meteorite impact.
shear field
   (Plasma Physics and Fusion Energy Glossary)
As used in plasma physics, this refers to magnetic fields having a rotational transform (or, alternatively, safety factor) that changes with radius (e.g., in the stellarator concept, magnetic fields that increase in pitch with distance from the magnetic axis.)
shear flow
   (Plasma Physics and Fusion Energy Glossary)
Fluid flow where the magnitude of the fluid velocity changes along a direction perpedicular to the direction of the fluidflow.
shear strain
   (NASA Thesaurus)
The tangent of the angular change, due to force, between two lines originally perpendicular to each other through a point in a body.
shear strength
   (NASA Thesaurus)
The maximum shear stress which a material is capable of sustaining. Shear strength is calculated from the maximum load during a shear or torsion test and is based on the original dimensions of the cross section of the specimen.
shear strength
   (NASA SP-7, 1965)
In materials, the stress required to produce fracture in the plane of cross section, the conditions of loading being such that the directions of force and of resistance are parallel and opposite although their paths are offset a specified minimum amount.
shear stress
   (NASA Thesaurus)
The stress component tangential to the plane on which the forces act. Used for shear fatigue and shearing stress.
shear wave
   (NASA SP-7, 1965)
A wave in an elastic medium which causes an element of the medium to change its shape without a change of volume. Mathematically, a shear wave is one whose velocity field has zero divergence. Also called rotational wave.
A shear plane wave in an isotropic medium is called a transverse wave.
shearography
   (NASA Thesaurus)
An interferomic method that provides whole field observation of derivatives of small surface displacement and hence, strain.
sheath
   (NASA SP-7, 1965)
= plasma sheath.
sheet molding compounds
   (NASA Thesaurus)
Resin matrix of polymer matrix fiber composites formed into sheets and used as molding materials for structures.
shell
   (NASA SP-7, 1965)
A body one of whose dimensions is small compared with the others.
shellfish
   (NASA Thesaurus)
Aquatic invertebrate animals having shells.
shepherd satellite
   (Planetary Rings Glossary - ARC)
The gravitational influence of a moon in orbit near the edge of a planetary ring can have the effect of repelling the ring material. This "shepherding" effect has been found to confine a number of rings in the solar system, and the moons that do the shepherding are called shepherd satellites.
shergottites
   (NASA Thesaurus)
Achondritic stony meteorites composed mainly of pigeonite and maskolynite.
shield
   (NASA SP-7, 1965)
A body of material used to prevent or reduce the passage of particles or radiation.
A shield may be designated according to what it is intended to absorb, as a gamma-ray shield or neutron shield, or according to the kind of protection it is intended to give, as a background, biological, or thermal shield. The shield of a nuclear reactor is a body of material designed to prevent the escape of neutrons and radiation into a protected area, which frequently is the entire space external to the reactor. It may be required for the safety of personnel or to reduce radiation sufficiently to allow use of counting instruments.
shield volcanoes
   (Photoglossary of Volcanic Terms - USGS)
Volcanoes with broad, gentle slopes and built by the eruption of fluid basalt lava are called shield volcanoes. Basalt lava tends to build enormous, low-angle cones because it flows across the ground easily and can form lava tubes that enable lava to flow tens of kilometers from an erupting vent with very little cooling. The largest volcanoes on Earth are shield volcanoes. The name comes from a perceived resemblance to the shape of a warrior's shield.
shielding
   (NASA Thesaurus / NASA SP-7, 1965)
The arrangement of shields used for any particular circumstances; the use of shields.
shimmer
   (NASA SP-7, 1965)
= terrestrial scintillation.
ship to shore communication
   (NASA Thesaurus)
Communication between a ship at sea and a shore station.
Shiva laser system
   (NASA Thesaurus)
High energy multi-arm solid state (Nd doped ED-2 glass) infrared laser system used for laser driven fusion experiments.
shock
   (NASA Thesaurus)
(physiology) Clinical manifestations of circulatory insufficiency, including hypotension, weak pulse, tachycardia, pallor, and diminished urinary output.
shock
   (NASA SP-7, 1965)
1. = shock wave.
2. A blow, impact, collision, or violent jar.
3. A sudden agitation of the mental or emotional state or an event causing it.
4. The sudden stimulation caused by an electrical discharge on the animal or human organism (e.g., electric shock).
shock absorber
   (NASA Thesaurus / NASA SP-7, 1965)
A device for the dissipation of energy used to modify the response of a mechanical system to applied shock.
shock front
   (NASA Thesaurus / NASA SP-7, 1965)
1. A shock wave regarded as the forward surface of a fluid region having characteristics different from those of the region ahead of the wave.
2. The front side of a shock wave.
shock isolator
   (NASA SP-7, 1965)
A resilient support that tends to isolate a system from applied shock. Also called shock mount.
shock mount
   (NASA SP-7, 1965)
= shock isolator.
shock spectrum
   (NASA Thesaurus / NASA SP-7, 1965)
A plot of the maximum acceleration experienced by a single-degree-of-freedom system as a function of its own natural frequency in response to an applied shock.
shock tube
   (NASA Thesaurus / NASA SP-7, 1965)
A relatively long tube or pipe in which very brief high-speed gas flows are produced by the sudden release of gas at very high pressure into a low-pressure portion of the tube; the high-speed flow moves into the region of low pressure behind a shock wave.
shock tunnel
   (NASA Thesaurus / NASA SP-7, 1965)
A shock tube used as a wind tunnel.
shock wave
   (NASA Thesaurus / NASA SP-7, 1965)
A surface or sheet of discontinuity (i.e., of abrupt changes in conditions) set up in a supersonic field or flow, through which the fluid undergoes a finite decrease in velocity accompanied by a marked increase in pressure, density, temperature, and entropy, as occurs, e.g., in a supersonic flow about a body. Sometimes called a shock. See attached shock wave, bow wave, condensation shock wave, detached shock wave, Mach wave, normal shock wave, oblique shock wave.
Shodop (abbr)
   (NASA SP-7, 1965)
= short-range Doppler.
Shoemaker-Levy 9 comet
   (Galileo Project Glossary - JPL)
The comet that broke up and fell into Jupiter in June 1994.
shooting star
   (NASA SP-7, 1965)
= meteor.
Shoran
   (NASA Thesaurus / NASA SP-7, 1965)
(From short-range navigation). A precision electronic position fixing system using a pulse transmitter and receiver and two transponder beacons at fixed points. High- precision shoran is called hiran.
short circuit currents
   (NASA Thesaurus)
The steady value of the input alternating currents that flow when the output direct current terminals are short-circuited and rated line alternating voltage is applied to the line terminals.
short circuits
   (NASA Thesaurus)
An abnormal connection of relatively low resistance between two points on a circuit. The result is a flow of excess (often damaging) current between these points.
short-baseline system
   (NASA SP-7, 1965)
A trajectory measuring system using a base line the length of which is very small compared with the distance of the object being tracked.
short-period error
   (NASA SP-7, 1965)
= random error.
short-range Doppler
   (NASA SP-7, 1965)
(abbr Shodop)
A short range trajectory measuring system using the intersections of the ellipsoids of Dovap and the hyperboloids of Dovap elsse or telemetry elsse during a rocket launch.
short-range navigation
   (NASA SP-7, 1965)
= shoran.
short-wave radiation
   (NASA SP-7, 1965)
In meteorology, a term used loosely to distinguish radiation in the visible and near-visible portions of the electromagnetic spectrum (roughly 0.4 to 1.0 micron in wavelength) from long-wave radiation ( infrared radiation).
shot
   (NASA SP-7, 1965)
1. An act or instance of firing a rocket, especially from the earth's surface, as, the shot carried the rocket 200 miles.
2. The flight of a rocket, as, the rocket made a 200-mile shot.
shot noise
   (NASA Thesaurus)
Quantum noise caused by electric current fluctuations attributable to the discrete nature of charge carriers.
shoulder harness
   (NASA SP-7, 1965)
A harness that fastens over a person's shoulders to prevent his being thrown forward in his seat. See lap belt.
shower
   (NASA SP-7, 1965)
= air shower (cosmic rays).
shutdown
   (NASA Thesaurus / NASA SP-7, 1965)
The process of decreasing engine thrust to zero.
shutoff
   (NASA SP-7, 1965)
= fuel shutoff.
Shuttle Derived Vehicles
   (NASA Thesaurus)
New configuration resulting from the production and operation of the Space Shuttle. Used for SDV.
Shuttle Engineering Simulator
   (NASA Thesaurus)
Training equipment for crew members in mission operation procedures including various approach maneuvers, braking, final approach, etc.
Shuttle pallet satellites
   (NASA Thesaurus)
Reusable pallet type structures designed to be shuttle launched which will act as building blocks for larger platforms. Used for SPAS (ESA platforms).
SI (abbr)
   (NASA SP-7, 1965)
= International System of Units.
sialon
   (NASA Thesaurus)
Any composition containing silicon, aluminum, oxygen, and nitrogen and usually produced by the high-temperature reactions among the ingredients.
SID (abbr)
   (NASA SP-7, 1965)
= sudden ionospheric disturbance.
side lobe
   (NASA SP-7, 1965)
See lobe.
sideband
   (NASA SP-7, 1965)
1. Either of the two frequency bands on both sides of the carrier frequency within which fall the frequencies of the wave produced by the process of modulation.
2. The wave components lying within such a band.
sidereal
   (NASA SP-7, 1965)
Of or pertaining to the stars.
Although sidereal generally refers to the stars and tropical to the vernal equinox, sidereal time and the sidereal day are based upon the position of the vernal equinox relative to the meridian. The sidereal year is based upon the stars.
sidereal day
   (NASA SP-7, 1965)
The duration of one rotation of the earth on its axis, with respect to the vernal equinox. It is measured by successive transits of the vernal equinox over the upper branch of a meridian.
Because of the precession of the equinoxes, the sidereal day thus defined is slightly less than the period of rotation with respect to the stars, but the difference is less than 0.01 second. The length of the mean sidereal day is 24 hours of sidereal time or 23 hours 56 minutes 4.09054 seconds of mean solar time.
sidereal hour angle
   (NASA SP-7, 1965)
Null
sidereal month
   (NASA SP-7, 1965)
The average period of revolution of the moon with respect to the stars, a period of 27 days 7 hours 43 minutes 11.5 seconds, or approximately 27 1/3 days.
sidereal period
   (NASA SP-7, 1965)
1. The time taken by a planet or satellite to complete one revolution about its primary as seen from the primary and as referred to a fixed star.
2. Specifically, the interval between two successive returns of an earth satellite in orbit to the same geocentric right ascension.
sidereal time
   (NASA Thesaurus / NASA SP-7, 1965)
Time based upon the rotation of the earth relative to the vernal equinox.
Sidereal time may be designated as local or Greenwich as the local or Greenwich meridian is used as the reference. When adjusted for nutation, to eliminate slight irregularities in the rate, it is called mean sidereal time.
sidereal year
   (NASA SP-7, 1965)
The period of one apparent revolution of the earth around the sun, with respect to the stars, averaging 365 days 6 hours 9 minutes 9.55 seconds in 1955, and increasing at the rate of 0.000095 second annually.
Because of the precession of the equinoxes this is about 20 minutes longer than a tropical year.
siderites
   (NASA Thesaurus)
A spathic iron ore; an iron carbonate.
sight
   (NASA SP-7, 1965)
= celestial observation.
sigma
   (NASA SP-7, 1965)
= standard deviation.
signal
   (NASA SP-7, 1965)
1. A visible, audible, or other, indication used to convey information.
2. The information to be conveyed over a communication system.
3. Any carrier of information; opposed to noise.
signal generators
   (NASA Thesaurus)
Shielded sources of voltage or power, the outpUt level and frequency of which are calibrated, and usually variable over a range.
signal strength
   (NASA SP-7, 1965)
In radio, a measure of the received radiofrequency power, generally expressed in decibels relative to some standard value, normally either 1 milliwatt or that power which would have resulted at the same distance under free-space transmission. Also called field strength.
signal to noise ratios
   (NASA Thesaurus)
Ratios which measure the comprehensibility of a data source or transmission link, usually expressed as the root mean square signal amplitude divided by the root mean square noise amplitude.
signal transmission level
   (NASA SP-7, 1965)
In a transmission system, the signal level, of a kind to be specified, at a designated position in the system.
The signal level at some specified position near the source may be taken as the zero reference level. In an acoustic system the signal level is often in the form of a sound pressure level; either the reference sound pressure or the reference sound pressure level must be specified.
signal velocity
   (NASA SP-7, 1965)
See velocity of propagation, note.
signal-to-noise ratio
   (NASA SP-7, 1965)
(abbr SNR or S/N). A ratio which measures the comprehensibility of a data source or transmission link, usually expressed as the root-mean-square signal amplitude divided by the root-mean-square noise amplitude.
The higher the S/N ratio, the less the interference with reception.
signs
   (NASA SP-7, 1965)
See zodiac.
silica gel
   (NASA Thesaurus)
A colloidal, highly absorbent silica used as a dehumidifying and dehydrating agent, as a catalyst carrier, and sometimes as a catalyst.
silicates
   (Galileo Project Glossary - JPL)
A group of minerals constituting about 95% of the Earth's crust, and containing silicon and oxygen combined with one or more other elements.
silicon dioxide
   (NASA Thesaurus)
The chemically resistant dioxide of silicon. Used for Refrasil (trademark) and silica.
silver hydrogen batteries
   (NASA Thesaurus)
Secondary batteries having silver and hydrogen electrodes. They have good energy density and cycle life.
silver-cell battery
   (NASA SP-7, 1965)
A type of short-duration, high-power-density battery of light weight used for single-time, high-power applications in vehicles where weight is critical.
silver-disk pyrheliometer
   (NASA SP-7, 1965)
An instrument used for the measurement of direct solar radiation. See pyrheliometer.
It is constructed in the following manner. A silver disk located at the lower end of a diaphragmed tube serves as the radiation receiver for a calorimeter. Radiation falling on the silver disk is periodically intercepted by means of a shutter located in the tube, causing temperature fluctuations of the calorimeter which are proportional to the intensity of the radiation. The instrument is normally used as a secondary instrument and is calibrated against the water-flow pyrheliometer. It is used by the U.S. Weather Bureau as a standard instrument.
silviculture
   (NASA Thesaurus)
The theory and practice of controlling the establishment, composition, and growth of stands of trees for the harvesting of foliage limbs, and possibly the trees themselves for biomass.
SIMD (computers)
   (NASA Thesaurus)
A type of parallel computer with multiple memories and an arithmetic logic unit for each memory. A single control unit allocates instruction execution according to the memory that holds the required operands. Used for single instruction multiple datastream.
simple average
   (NASA SP-7, 1965)
See arithmetic mean, sense 2.
simple harmonic motion
   (NASA Thesaurus / NASA SP-7, 1965)
A motion such that the displacement is a sinusoidal function of time.
simple harmonic quantity
   (NASA SP-7, 1965)
A periodic that is a sinusoidal function of the independent variable. Thus,

y = A sin ( lower case omega x + lower case phi )

where y is the simple harmonic quantity; A is the amplitude; is the angular frequency; x is the independent variable; and lower case phi is the phase of the oscillation.
The maximum value of the simple harmonic quantity is the amplitude A; it is sometimes called, for emphasis, the single amplitude to distinguish it from double amplitude which for a simple harmonic quantity is the same as the total excursion or peak-to-peak value. When a simple harmonic quantity is expressed as a complex quantity, the term amplitude must be used with caution in view of possible confusion with the alternate meaning of amplitude as the angle or argument of a complex quantity.
simple reflection
   (NASA SP-7, 1965)
= specular reflection.
simple reflector
   (NASA SP-7, 1965)
= specular reflector.
simple standard deviation
   (NASA SP-7, 1965)
See standard deviation.
simplex method
   (NASA Thesaurus)
A finite iterative algorithm used in linear programming whereby successive solutions are obtained and tested for optimality.
sine wave
   (NASA Thesaurus / NASA SP-7, 1965)
A wave which can be expressed as the sine of a linear function of time, or space, or both.
single channel per carrier transmission
   (NASA Thesaurus)
Voice and data transmission system for satellite communication featuring the use of a carrier frequency for each channel of communication. Used for SCPC transmission.
single event upsets
   (NASA Thesaurus)
Radiation-induced errors in microelectronic circuits caused when charged particles (usually from the radiation belts or from cosmic rays) lose energy by ionizing the medium through which they pass, leaving behind a wake of electron-hole pairs.
single sheath
   (NASA SP-7, 1965)
See plasma sheath, note.
single stage to orbit vehicles
   (NASA Thesaurus)
Second and third generation (post-Space Shuttle) vehicles studied for Earth orbit international space transportation system.
single-degree-of-freedom system
   (NASA SP-7, 1965)
A mechanical system for which only one coordinate is required to define completely the configuration of the system at any instant. See degree of freedom.
single-entry compressor
   (NASA SP-7, 1965)
A centrifugal compressor that takes in air or fluid on only one side of the impeller, the impeller being faced with vanes only on that side.
single-sideband modulation
   (NASA SP-7, 1965)
Modulation whereby the spectrum of the modulating wave is translated in frequency by a specified amount either with or without inversion.
single-sideband transmission
   (NASA SP-7, 1965)
That method of operation in which one sideband is transmitted and the other sideband is suppressed. The carrier wave may be either transmitted or suppressed.
single-stage compressor
   (NASA SP-7, 1965)
A centrifugal compressor having a single impeller wheel, with vanes either on one or on both sides of the wheel; also, an axial flow compressor with one row of rotor blades and one row of stator blades. Axial-flow compressors are normally multistage.
single-stage rocket
   (NASA SP-7, 1965)
A rocket vehicle provided with a single rocket propulsion system. See stage.
singularity
   (High Energy Astrophysics Dictionary- GSFC)
The center of a black hole, where the curvature of spacetime is maximal. At the singularity, the gravitational tides diverge; no solid object can even theoretically survive hitting the singularity. Although singularities generally predict inconsistencies in theory, singularities within black holes do not necessarily imply that general relativity is incomplete so long as singularities are always surrounded by event horizons. A proper formulation of quantum gravity may well avoid the classical singularity at the centers of black holes.
singularity
   (Spacetime Wrinkles Glossary)
In the center of the mathematical model of a black hole is a singularity which has the shape of a point (or a ring if the hole is rotating), at which the curvature of spacetime becomes infinitely large. A singularity represents a great difficulty for theoreticians because it is impossible to predict how a singularity will affect objects in its causal future. If cosmic censorship is true, then this needn't cause any trouble because they will only be found inside event horizons
sink
   (NASA SP-7, 1965)
1. In the mathematical representation of fluid flow, a hypothetical point or place at which the fluid is absorbed.
2. A heat sink. See source.
sinkholes
   (NASA Thesaurus)
Circular depressions in a Karst area. Their drainage is subterraneous, their size is measured in meters or tens of meters, and they are commonly funnel shaped.
sinking
   (NASA SP-7, 1965)
In atmospheric optics, a refraction phenomenon, the opposite of looming, in which an object on or slightly above the geographic horizon apparently sinks below it. Compare inferior mirage, stooping.
Sinking occurs whenever the rate of density decreases with height through the atmosphere is of smaller magnitude than normal or, in extreme cases, where the density actually increases with height.
Sinope
   (NASA Thesaurus)
A natural satellite of Jupiter orbiting at a mean distance of 23,700,000 kilometers.
sintered ceramic
   (NASA SP-7, 1965)
A ceramic body or coating prepared by heating a ceramic powder below its melting point but at a sufficiently high temperature to cause interdiffusion of ions between contacting particles and subsequent adherence at the points of contact.
sintering
   (NASA Thesaurus / NASA SP-7, 1965)
The bonding of adjacent surfaces of particles in a mass of powders, usually metal, by heating.
sinus
   (NASA SP-7, 1965)
A hollow or cavity; a recess or pocket. Specifically, sinuses: air cavities lined by mucous membrane which communicate with the nasal cavity; the ethmoidal, frontal, sphenoidal, and maxillary sinuses.
sinus barotrauma
   (NASA SP-7, 1965)
= aerosinusitis.
sinuses
   (NASA Thesaurus)
A term used in anatomical nomenclature to designate a cavity or hollow space.
sinusoidal
   (NASA SP-7, 1965)
Having the form of a sine wave.
siphoning
   (NASA Thesaurus)
The transfer of a liquid from a high to a lower level by atmospheric pressure forcing it up the shorter leg while the weight of the liquid in the longer leg causes continuous downward flow.
SIRTF
   (Space Flight Glossary - JPL)
Space Infrared Telescope Facility.
SIS (semiconductors)
   (NASA Thesaurus)
Semiconductor devices consisting of an electrically insulating layer sandwiched between two semiconducting materials. Used for semiconductor insulator semiconductors.
site selection
   (NASA Thesaurus)
Selecting the location for any physical plant (nuclear power, solar house, etc.) while considering the environmental impact, safety, etc.
size distribution
   (NASA Thesaurus)
The study of the size of objects or features and their distribution.
skiatron
   (NASA SP-7, 1965)
1. A dark trace oscilloscope tube. See dark trace tube.
2. A display employing an optical system with a dark trace tube.
skimmer basin
   (NASA SP-7, 1965)
= deluge collection pond.
skin
   (NASA SP-7, 1965)
The covering of a body, of whatever material, such as the covering of a fuselage, of a wing, of a hull, of an entire aircraft, etc.; a body shell, as of a rocket; the surface of a body.
skin temperature
   (NASA SP-7, 1965)
The outer surface temperature of a body.
skin tracking
   (NASA SP-7, 1965)
The tracking of an object by means of radar without using a beacon or other signal device on board the object being tracked.
skip effect
   (NASA SP-7, 1965)
A phenomenon in which sound or radio energy may be detected only at various distance intervals from the energy source as the result of the presence of an energy reflecting or refracting layer in the atmosphere. See radio duct.
For long radio waves, the ionosphere acts as the reflecting layer. For shorter wavelengths, the effect may be produced by strong superstandard propagation in elevated layers of the troposphere. Skip effects make it possible on occasion to detect targets at distances far greater than the normal radio horizon, while closer targets remain undetected.
skirt
   (NASA SP-7, 1965)
The lower outer part of a rocket vehicle; specifically, the half-stage of an Atlas.
skirt fog
   (NASA SP-7, 1965)
The cloud of steam and water that surrounds the engines of a rocket being launched from a wet emplacement.
sky light
   (NASA SP-7, 1965)
= diffuse sky radiation.
sky radiation
   (NASA SP-7, 1965)
= diffuse sky radiation.
sky screen
   (NASA SP-7, 1965)
An optical device used to detect the departure of a rocket from its intended trajectory.
sky wave
   (NASA Thesaurus / NASA SP-7, 1965)
In radio, radio energy that is received after having been reflected by the ionosphere. Compare wave.
skyhook balloon
   (NASA Thesaurus / NASA SP-7, 1965)
(Originally a code name for a U.S. Navy Project.) A large free balloon having a plastic envelope, used especially for constant-level meteorological observations at very high altitudes.
slant range
   (NASA SP-7, 1965)
The line-of-sight range of a radar or radio. See range.
slave
   (NASA SP-7, 1965)
1. = slave station.
2. Device that follows an order given by a master station through remote control.
slave antenna
   (NASA SP-7, 1965)
A directional antenna that is positioned in azimuth and elevation by a servo system. The information controlling the servosystem is supplied by a tracking or positioning system.
slave station
   (NASA SP-7, 1965)
In a hyperbolic navigation system, a station whose transmissions are controlled by a master station. Often shortened to slave. See hyperbolic navigation.
slaving
   (NASA SP-7, 1965)
Of a gyro, the use of a torquer to maintain the orientation of the spin axis relative to an external reference such as a pendulum or magnetic compass.
sleeve-dipole antenna
   (NASA SP-7, 1965)
A dipole antenna surrounded in its central portion by a coaxial sleeve.
slenderness ratio
   (NASA SP-7, 1965)
A dimensionless number expressing the ratio of a rocket vehicle length to its diameter.
slew
   (NASA SP-7, 1965)
To change the position of an antenna or range gear assembly by injecting a synthetic error signal into the positioning servo amplifier.
slewing
   (NASA Thesaurus / NASA SP-7, 1965)
1. Of a gyro, the rotation of the spin axis caused by applying torque about the axis of rotation.
2. In radar, changing the scale on the display.
slides (microscopy)
   (NASA Thesaurus)
Rectangular pieces of glass on which objects are mounted for microscopic examination.
sliding
   (NASA Thesaurus)
Relative displacement between two bodies along a surface, without loss of contact between the bodies.
slip
   (NASA SP-7, 1965)
A sprayable slurry comprising a frit suspended in a liquid carrier (sometimes also used for dip and brush coating).
slip flow
   (NASA Thesaurus)
Rarefied gas flow in the region between Knudsen numbers 0.01 and 0.1.
slip flow
   (NASA SP-7, 1965)
See rarefied gas dynamics, note.
slope angle
   (NASA SP-7, 1965)
The angle in the vertical plane between the flightpath and the horizontal.
slopes
   (NASA Thesaurus)
The inclined surfaces of any part of the Earth's surface, as in hillslopes; also broad parts of a continent descending toward an ocean, as in the Pacific slope. Used for cant, slant, and steepness.
sloshing
   (NASA SP-7, 1965)
The back-and-forth movement of a liquid fuel in its tank, creating problems of stability and control in the vehicle.
slow ion
   (NASA SP-7, 1965)
= large ion.
sludge
   (NASA Thesaurus)
A water-formed sedimentary deposit.
slug
   (NASA SP-7, 1965)
A unit of mass; the mass of a free body which if acted upon by a force of 1 pound would experience an acceleration of 1 foot per square second; thus approximately 32.16 pounds.
slurry
   (NASA SP-7, 1965)
A suspension of fine solid particles in a liquid.
slurry fuel
   (NASA SP-7, 1965)
A fuel consisting of a suspension of fine solid particles in a liquid.
small calorie
   (NASA SP-7, 1965)
(abbr cal)
See calorie.
small circle
   (NASA SP-7, 1965)
The intersection of a sphere and a plane which does not pass through the center of the sphere, as a parallel of latitude.
small ion
   (NASA SP-7, 1965)
An atmospheric ion, apparently a singly charged atmospheric molecule (or, rarely, an atom) about which a few other neutral molecules are held by the electrical attraction of the central ionized molecule. Estimates of the number of satellite molecules range as high as 12. Also called light ion, fast ion.
Small ions may disappear either by direct recombination with oppositely charged small ions or by combination with neutral Aitken nuclei to form new large ions, or by combination with large ions of opposite sign. The small ion, collectively, is the principal agent of atmospheric conduction.
small perturbation
   (NASA SP-7, 1965)
A disturbance imposed on a system in steady state, with amplitude assumed small, i.e., the square of the amplitude is negligible in comparison with the amplitude, and the derivatives of the perturbation are assumed to be of the same order of magnitude as the perturbation. See perturbation, method of small perturbations.
smart materials
   (NASA Thesaurus)
Engineered materials capable of responding to their environment to a significant degree, by virtue of intrinsic properties and/or built-in sensor/actuator elements. Applications of these materials include vibration suppression/isolation, precision positioning, damage detection, and tunable devices.
smart structures
   (NASA Thesaurus)
Structures and/or structural components which contain embedded internal sensors. The sensors serve as lifetime health monitors analogous to a central nervous system, and give information on structural properties, providing real time nondestructive evaluation.
smoldering
   (NASA Thesaurus)
A slow, flameless combustion of a solid fuel.
SMS 1
   (NASA Thesaurus)
A meteorological satellite in synchronous orbit over the Atlantic Ocean to give coverage to the Eastern US. It was launched in May 1974 and is no longer operational, but still in orbit.
SMS 2
   (NASA Thesaurus)
Meteorological satellite in synchronous orbit over Honolulu to give coverage to the Western US. It was launched in February 1975 and is no longer operational, but still in orbit.
SNC meteorites
   (NASA Thesaurus)
Meteorites with petrologic characteristics, isotopic signatures, trapped gas compositions, and relatively young crystallization ages (less than 1.3 billion years), which together point to a Martian origin. The name of these meteorites is derived from first three known examples-- Shergotty, Nakhla, and Chassigny.
sneak circuit analysis
   (NASA Thesaurus)
In electrical or electronic circuits, the detection and/or prevention of "sneak circuits" -- paths having latent electrical conditions resulting from unapparent stimulus-response relationships which cause unwanted functions or inhibit desired function.
Snell law
   (NASA SP-7, 1965)
See refraction, index of refraction.
Snells law
   (NASA Thesaurus)
A law of geometric optics that defines the amount of bending that takes place when a light ray strikes a refractive boundary (e.g., an air-glass interface) at a non-normal angle.
Snort track
   (NASA SP-7, 1965)
A rail track on which a supersonic rocket sled is driven, located at the Naval Ordnance Test Station.
snow
   (NASA Thesaurus)
A form of ice composed of small white or translucent hexagonal crystals of frozen water, formed directly by sublimation of atmospheric water vapor around solid nuclei at a temperature below the freezing point. The crystals grow while floating or falling to the ground, and are often agglomerated into snowflakes.
snow
   (NASA SP-7, 1965)
= grass.
SNR
   (Space Flight Glossary - JPL)
Signal-to-Noise Ratio.
snubber
   (NASA SP-7, 1965)
A device used to increase the stiffness of an elastic system, usually by a large factor, whenever the displacement becomes larger than a specified amount.
Sobolev space
   (NASA Thesaurus)
A Banach space whose elements are functions defined in a domain in Euclidean space and whose norm measures the size and smoothness of the functions.
sod
   (NASA Thesaurus)
The top stratum of soil usually containing grassy plants with their matted roots.
sodar
   (NASA Thesaurus)
Sound detecton and ranging.
sodium sulfates
   (NASA Thesaurus)
Sodium compounds containing the -SO4 group.
sodium sulfur batteries
   (NASA Thesaurus)
One of several types of rechargeable batteries under consideration as power sources for electrically actuated vehicles. This battery uses a solid electrolyte as well as a sodium reservoir made of metal.
SOE
   (Space Flight Glossary - JPL)
Sequence of Events.
sofar
   (NASA SP-7, 1965)
(From sound fixing and ranging). A system of navigation providing hyperbolic lines of position determined by shore listening stations which receive sound signals produced by depth charges dropped at sea and exploding in a sound channel which is at a considerable depth in most areas.
This system is used in Project Mercury for locating spacecraft down at sea.
soft gamma repeaters
   (NASA Thesaurus)
A class of x-ray source which emits repeating bright bursts of "soft" or low-energy gamma rays, along with steady x-ray pulsations. By the end of 1999 only a handful of these sources had been identified, in our galaxy and in the Large Magellanic Cloud. They are associated with supernova remnants and are thus apparently some kind of young neutron star. One theory holds that these stars are young magnetars (magnetically-powered neutron stars). Bright bursts occur when the evolving, ultra-strong magnetic field stresses the neutron star's solid crust to breaking, in a sudden starquake. x-ray pulsations are due to the rotation of the star, with it's hot surface bright in x-rays.
soft landing
   (NASA Thesaurus / NASA SP-7, 1965)
The act of landing on the surface of a planet without damage to any portion of the vehicle or payload except possibly the landing gear.
soft radiation
   (NASA SP-7, 1965)
Radiation absorbable by an absorber equivalent to 10 centimeters of lead or less.
Radiation which can penetrate more than 10 centimeters of lead is termed hard radiation.
softening range
   (NASA SP-7, 1965)
An arbitrarily defined temperature range below the crystal melting point where a ceramic becomes soft and noticeably viscous; a softening range rather than a sharp melting point occurs in ceramics containing a glass base.
software development tools
   (NASA Thesaurus)
Computer programs that aid in the specification, construction, testing, analysis, managment, documentation, and maintenance of other computer programs.
software engineering
   (NASA Thesaurus)
The systematic approach to the development, operation, maintenance, and retirement of software.
SOHO Mission
   (NASA Thesaurus)
One of the joint NASA/ESA missions comprising the International Solar Terrestrial Program. The SOHO Mission will investigate the physical processes in the solar corona and solar wind and the structure and dynamics of the solar interior.
SOI (semiconductors)
   (NASA Thesaurus)
Semiconductor devices consisting of a silicon layer coupled to an electrically insulating layer. Used for silicon-on-insulator semiconductors.
soil classification
   (Global Land Information System Glossary - USGS)
The systematic arrangement of soils into groups or categories based on their characteristics. Broad groupings are made on the basis of general characteristics and subdivisions on the premise of more detailed differences in specific properties.
soil mechanics
   (NASA Thesaurus)
Mechanical properties of unconsolidated accumulations of particles produced by the disintegration and chemical decomposition of rocks.
soil phase
   (Global Land Information System Glossary - USGS)
A subdivision of a soil classification, usually a soil series or other unit based on characteristics that affect the use and management of the soil but which do not vary sufficiently to differentiate it as a separate soil series.
solar
   (NASA SP-7, 1965)
1. Of or pertaining to the sun or caused by the sun, as solar radiation, solar atmospheric tide.
2. Relative to the sun as a datum or reference , as solar time.
solar activity
   (NASA Thesaurus / NASA SP-7, 1965)
Any type of variation in the appearance or energy output of the sun. See faculae, flare, flocculi, granules, prominence, spicules, sunspot.
solar air mass
   (NASA SP-7, 1965)
The optical air mass penetrated by light from the sun for any given position of the sun in the sky.
solar antapex
   (NASA SP-7, 1965)
See solar apex.
solar apex
   (NASA SP-7, 1965)
The point on the celestial sphere toward which the sun is traveling. Also called apex of the sun's way.
The solar apex is at approximately right ascension 270 degrees declination 34 degrees N. The point diametrically opposite the solar apex on the celestial sphere is the solar antapex, right ascension 90 degrees declination 34 degrees S.
solar atmosphere
   (Solar Physics Glossary - NASA GSFC)
The atmosphere of the Sun. An atmosphere is generally the outermost gaseous layers of a planet, natural satellite, or star. Only bodies with a strong gravitational pull can retain an atmosphere. Atmosphere is used to describe the outer layer of the Sun because it is relatively transparent at visible wavelengths. Parts of the solar atmosphere include the photosphere, chromosphere, and the corona.
solar atmospheric tide
   (NASA SP-7, 1965)
An atmospheric tide due to the thermal or gravitational action of the sun.
Six and eight hour components of small amplitude have been observed. They are primarily thermal in origin. The 12-hour component has by many times the greatest amplitude of any atmospheric tidal component, about 1.5 millibars at the equator and 0.5 millibar in middle latitudes. This relatively large amplitude is often explained as a resonance effect. The 24-component is a thermal tide with great local variability.
solar atriums
   (NASA Thesaurus)
Open courts within buildings designed for passive solar heating.
Solar Backscatter UV Spectrometer
   (NASA Thesaurus)
A spaceborne spectrometer that measures solar UV spectral irradiance incident on the Earth and backscattered radiance from the Earth and thereby estimates the total atmospheric ozone content of the atmosphere and the attitude distribution of ozone.
solar blankets
   (NASA Thesaurus)
Large, high-temperature, low-mass solar arrays consisting of ultrathin silicon solar cells interconnected, welded, and bonded to flexible substances.
solar cell
   (NASA SP-7, 1965)
A photovoltaic cell that converts sunlight into electrical energy.
Solar Cell Calibration Facility
   (NASA Thesaurus)
One of the spacelab payloads. Used for SCCF.
solar cells
   (NASA Thesaurus)
Photovoltaic cells that convert sunlight into electrical energy. Used for silicon solar cells and wraparound contact solar cells.
solar collectors
   (NASA Thesaurus)
Devices designed to absorb incident solar radiation and transfer the energy to a fluid passing through it. Used for solar receivers.
solar constant
   (NASA Thesaurus / NASA SP-7, 1965)
The rate at which solar radiation is received outside the earth's atmosphere on a surface normal to the incident radiation and at the earth's mean distance from the sun.
Measurements of solar radiation at the earth's surface by the Smithsonian Institution for several decades give a best value for the solar constant of 1.934 calories per square centimeter per minute. Measurements from rockets of the intensity of the ultraviolet end of the spectrum have corrected this value to 2.00 calories per square centimeter per minute with a probable error of +/- 2 percent.
solar cooling
   (NASA Thesaurus)
Conversion of solar energy into refrigeration energy.
solar corona
   (Earth's Magnetosphere Glossary - GSFC)
The outermost layer of the Sunīs atmosphere, visible to the eye during a total solar eclipse; it can also be observed through special filters and best of all, by X-ray cameras aboard satellites.
solar corona
   (NASA SP-7, 1965)
See corona.
solar corpuscular rays
   (NASA SP-7, 1965)
Cosmic radiation supposedly originating in the sun. See corpuscular cosmic ray.
solar cosmic rays
   (NASA Thesaurus / NASA SP-7, 1965)
Cosmic rays supposedly originating in the sun.
solar cycle
   (From Stargazers to Starships Glossary - GSFC)
An irregular cycle, averaging about 11 years in length, during which the number of sunspots (and of their associated outbursts) rises and then drops again. Like the sunspots, the cycle is probably magnetic in nature, and the polar magnetic field of the Sun also reverses each solar cycle.
solar cycle
   (NASA SP-7, 1965)
The periodic increase and decrease in the number of sunspots. The cycle has a period of about 11 years.
solar day
   (NASA SP-7, 1965)
1. The duration of one rotation of the earth on its axis, with respect to the sun.
This may be either a mean solar day, or an apparent solar day, as the reference is the mean or apparent sun, respectively.
2. The duration of one rotation of the sun on its axis.
solar diameter
   (NASA Thesaurus)
Observable dimension of the sun.
solar dynamic power systems
   (NASA Thesaurus)
Electric power systems using a solar heated working fluid to drive a turboalternator. Primary applications are for space stations and spacecraft.
solar eclipse
   (NASA Thesaurus / NASA SP-7, 1965)
The obscuration of the light of the sun by the moon.
A solar eclipse is partial if the sun is partly obscured, total if the entire surface is obscured, or annular if a thin ring of the sun's surface appears around the obscuring body.
solar energetic particles
   (Earth's Magnetosphere Glossary - GSFC)
Energetic particles occasionally emitted from active areas on the Sun, associated with solar flare and coronal mass ejections. The Earthīs magnetic field keeps them out of regions close to Earth (except for the polar caps) but they can pose a hazard to space travelers far from Earth.
solar energy
   (NASA Thesaurus)
The radiant energy originating from the sun. Approximately 99% of solar energy lies between the wavelengths of 300 to 3,500 nm.
solar flares
   (NASA Thesaurus / NASA SP-7, 1965)
A rapid release of electromagnetic (visible, radio, ultraviolet, x ray) and particulate (protons, electrons) energy from the sun. Flares are classified according to the optically observed area of the solar surface covered, franging from zero for the smallest to 3 for the largest, and their intensity, either faint, noraml, or brilliant.
solar houses
   (NASA Thesaurus)
Habitable buildings designed with large expanses of glass or other transparent materials to collect solar radiation for heating.
solar limb
   (AS&T Dictionary)
The apparent edge of the Sun as it is seen in the sky.
solar longitude
   (AS&T Dictionary)
Angular distance along the Earth's orbit measured from the intersection of the ecliptic and the celestial equator where the Sun moves from south to north. It gives the position of the Earth on its orbit and, hence, is a more appropriate information on a meteoroid shower's maximum than the date.
solar mass
   (Imagine the Universe Dictionary - NASA GSFC)
A unit of mass equivalent to the mass of the Sun. 1 solar mass = 1 Msun = 2 x 1033 grams.

solar maximum
   (SOHO Glossary - GSFC)
The month(s) during the solar cycle when the number of sunspots reaches a maximum. The most recent solar maximum occurred in July 1989.
Solar Maximum Mission
   (NASA Thesaurus)
Use of the multimission modular spacecraft for the study of solar particles, emissions, and flares.
Solar Maximum Mission-A
   (NASA Thesaurus)
The solar maximum mission spacecraft. Used for SMM-A.
Solar Mesosphere Explorer
   (NASA Thesaurus)
A satellite whose experiments provided a comprehensive study of atmospheric ozone and the processes which form and destroy it. The satellite was launched in October of 1981. On May 15, 1989, the mission was terminated due to battery problems.
solar minimum
   (SOHO Glossary - GSFC)
The month(s) during the solar cycle when the number sunspots is lowest. The most recent minimum occurred in 1996.
solar neighborhood
   (NASA Thesaurus)
The portion of the Milky Way Galaxy centering around the sun and containing the nearest neighboring stars.
solar neutrinos
   (NASA Thesaurus)
Neutral particles originating from nuclear reactions in the core of the sun.
solar optical telescope
   (NASA Thesaurus)
A 1-M class, high resolution solar telescope which NASA had planned to operate on the Shuttle Spacelab during the mid and late 1980s. Used for SOT.
solar oscillations
   (NASA Thesaurus)
Irregular oscillations in the solar atmosphere.
solar parallax
   (NASA Thesaurus / NASA SP-7, 1965)
The angle at the sun subtended by the equatorial diameter of the earth. See parallax.
The adopted value of the solar parallax in the system of astronomical constants is 8.80 seconds of arc.
solar physics
   (NASA Thesaurus)
The study of the structure and activities of the Sun.
solar planetary interactions
   (NASA Thesaurus)
The interactions and subsequent effects caused by the interactions of solar activity and/or wind with a planet, its magnetic field, its atmosphere, or natural satellites.
solar ponds (heat storage)
   (NASA Thesaurus)
Large, shallow ponds covered with thin, transparent plastic shields and used for collecting and storing solar heat for conversion to electric power.
solar power satellites
   (NASA Thesaurus)
Proposed very large space structures consisting of hundreds of square miles of solar thermal collectors and/or photovoltaic converters constructed or assembled in space. Power would be transmitted to Earth in microwave form.
solar powered aircraft
   (NASA Thesaurus)
Aircraft powered by solar energy.
solar prominence
   (NASA Thesaurus)
Filamentlike protuberances from the chromosphere of the sun. Used for filaments (solar physics).
solar prominence
   (NASA SP-7, 1965)
= prominence.
solar protons
   (NASA SP-7, 1965)
Protons emitted by the sun, especially during solar flares.
solar radiation
   (NASA Thesaurus / NASA SP-7, 1965)
The total electromagnetic radiation emitted by the sun. See insolation, direct solar radiation, diffuse sky radiation, global radiation, extraterrestrial radiation, solar constant.
To a first approximation, the sun radiates as a blackbody at a temperature of about 5700 degrees K; hence about 99.9 percent of its energy output falls within the wavelength interval from 0.15 micron to 4.0 microns, with peak intensity near 0.47 micron. About one-half of the total energy in the solar beam is contained within the visible spectrum from 0.4 to 0.7 micron, and most of the other half lies in the near infrared, a small additional portion lying in the ultraviolet.
solar radio burst
   (NASA Thesaurus / NASA SP-7, 1965)
A sudden increase in the flux from the sun at radio frequencies.
solar radio emission
   (NASA Thesaurus)
Radiation at radio frequencies originating from the sun or its corona. Used for solar noise and solar radio waves.
solar radio waves
   (NASA SP-7, 1965)
Radiation at radio frequencies originating in the sun or its corona.
solar simulator
   (NASA Thesaurus / NASA SP-7, 1965)
A device which produces thermal energy, equivalent in intensity and spectral distribution to that from the sun, used in testing materials and space vehicles.
solar system
   (NASA Thesaurus / NASA SP-7, 1965)
The sun and other celestial bodies within its gravitational influence, including planets, asteroids, satellites, comets, and meteors.
solar system evolution
   (NASA Thesaurus)
The origin and development of the solar system.
solar thermal electric power plants
   (NASA Thesaurus)
The use of solar energy to generate steam for producing electricity.
solar thermal propulsion
   (NASA Thesaurus)
Proposed energy source for spacecraft propulsion by passing hydrogen through a heat exchanger placed at the focal point of a large parabolic dish solar concentrator mirror.
solar tide
   (NASA SP-7, 1965)
See solar atmospheric tide.
solar time
   (NASA SP-7, 1965)
Time based upon the rotation of the earth relative to the sun.
Solar time may be designated as mean or astronomical if the mean sun is the reference, or apparent if the apparent sun is the reference. The difference between mean and apparent time is called equation of time. Solar time may be further designated according to the reference meridian, either the local or Greenwich meridian or additionally in the case of mean time, a designated zone meridian. Standard or daylight-saving are variations of zone time. Time may also be designated according to the timepiece, as chronometer time or watch time, the time indicated by these instruments.
solar total energy systems
   (NASA Thesaurus)
Systems for converting solar energy directly into electrical and thermal energy.
solar transition region
   (NASA Thesaurus)
A layer of the solar atmosphere only a few hundred miles thick between the chromosphere and the corona across which the temperature rises rapidly from a few times 10(exp 4) K to the order of 10(exp 6) K.
Solar Ultraviolet Measurements of Emitted Radiation
   (SOHO Glossary - GSFC)
An ultraviolet spectrometer aboard SOHO.
solar weather
   (Earth's Magnetosphere Glossary - GSFC)
The popular name for energy-releasing phenomena in the magnetosphere, associated with magnetic storms, substorms and interplanetary shocks.
solar wind
   (From Stargazers to Starships Glossary - GSFC)
A fast outflow of hot gas in all directions from the upper atmosphere of the Sun ("solar corona"), which is too hot to allow the Sun's gravity to hold on to its gas. Its composition matches that of the Sun's atmosphere (mostly hydrogen) and its typical velocity is 400 km/sec, covering the distance from Sun to Earth in 4-5 days.
solar wind
   (NASA Thesaurus / NASA SP-7, 1965)
Streams of plasma flowing approximately radially outward from the sun.
Solar Wind Anisotropies
   (SOHO Glossary - GSFC)
Instrument aboard SOHO which analyzes large scale variations in the solar wind by observing electromagnetic radiation given off by neutral hydrogen.
solar year
   (NASA SP-7, 1965)
= tropical year.
solar-radiation observation
   (NASA SP-7, 1965)
An evaluation of the radiation from the sun that reaches the observation point. The observing instrument is usually a pyrheliometer or pyranometer.
Two types of such observation are taken. The more common consists of measurements of the radiation reaching a horizontal surface, consisting of both radiation from the sun (direct solar radiation) and that reaching the instrument indirectly by scattering in the atmosphere (diffuse sky radiation). The other type of observation involves the use of an equatorial mount that keeps the instrument pointed directly at the sun at all times. The sensitive surface of the instrument is normal to the path of the radiation and is shielded from indirect radiation from the sky.
solarimeter
   (NASA SP-7, 1965)
1. = pyranometer.
2. Specifically, a pyranometer consisting of a Moll thermopile covered by a bell glass.
solenoid
   (Plasma Physics and Fusion Energy Glossary)
Cylindrical coil of wire which, when current flows through it, acts as an electromagnet. For long solenoids with many turns, the magnetic field inside the center isnearly uniform.
solenoid
   (NASA SP-7, 1965)
A tube formed in space by the intersection of unit-interval isotimic surfaces of two scalar quantities.
Solenoids formed by the intersection of surfaces of equal pressure and density are frequently referred to in meteorology. A barotropic atmosphere implies the absence of solenoids of this type, since surfaces of equal pressure and density coincide.
solettas
   (NASA Thesaurus)
Orbiting solar mirrors (reflectors).
solid angle
   (NASA SP-7, 1965)
(symbol lower case omega)
A portion of the whole of space about a given point, bounded by a conical surface with its vertex at that point and measured by the area cut by the bounding surface from the surface of a sphere of unit radius centered at that point. See steradian.
solid cryogen cooling
   (NASA Thesaurus)
Cooling with solidified cryogenic fluids.
solid cryogens
   (NASA Thesaurus)
Solidified cryogenic fluids.
solid electrolytes
   (NASA Thesaurus)
Single crystals, certain alloys, alkaline metals, and other compact compounds used in galvanic cells (batteries).
solid propellant
   (NASA Thesaurus / NASA SP-7, 1965)
Specifically, a rocket propellant in solid form, usually containing both fuel and oxidizer combined or mixed, and formed into a monolithic (not powered or granulated) grain.
solid propellant combustion
   (NASA Thesaurus)
The burning of solid propellants by rapid oxidation and production of expanding gases, heat, and light.
solid propellant engine
   (NASA SP-7, 1965)
= solid propellant rocket engine.
solid propellant rocket engines
   (NASA Thesaurus / NASA SP-7, 1965)
Rocket engines fueled with a solid propellant. Such motors consist essentially of a combustion chamber containing the propellant, and a nozzle for the exhaust jet, although they often contain other components, such as grids, liners, etc.
solid rocket
   (NASA SP-7, 1965)
A rocket that uses a solid propellant.
solid rocket fuel
   (NASA SP-7, 1965)
A solid propellant.
solid rotation
   (NASA SP-7, 1965)
The rotation of a system as though is were a solid or rigid body rotating about a fixed axis, all points within the body having the same angular velocity.
solid state lasers
   (Plasma Physics and Fusion Energy Glossary)
A laser using a transparent substance (crystalline or glass) as the active medium, doped to provide the energy states necessary for lasing. The pumping mechanism is the radiation from a powerful light source, such as a flashlamp.
solid state physics
   (NASA Thesaurus)
The study of the physical structure and properties of solid matter, including electrical conduction in metal crystals and semiconductors, superconductivity, and photoconductivity.
solid-state devices
   (NASA Thesaurus / NASA SP-7, 1965)
Devices which utilize the electric, magnetic, and photic properties of solid materials, e.g., binary magnetic cores, transistors, etc.
solitary waves
   (NASA Thesaurus)
Nonlinear waves capable of propagation without spreading out, breaking up, or dissipating their strength over distance. Used for Solitrons.
solitons solitons
   (Plasma Physics and Fusion Energy Glossary)
Stable, shape-preserving and localized solutions of nonlinear classical field equations. Of recent interest as possible models of extended elementary particles.
solstice
   (NASA Thesaurus / NASA SP-7, 1965)
1. One of the two points of the ecliptic farthest from the celestial equator; one of the two points on the celestial sphere occupied by the sun at maximum declination.
That in the northern hemisphere is called the summer solstice and that in the southern hemisphere the winter solstice. Also called solstitial point.
2. That instant at which the sun reaches one of the solstices, about June 21 (summer solstice) or December 22 (winter solstice).
solstitial colure
   (NASA SP-7, 1965)
That great circle of the celestial sphere through the celestial poles and the solstices.
solstitial point
   (NASA SP-7, 1965)
= solstice.
solvation
   (NASA Thesaurus)
The process of swelling, getting, or dissolving of a material by a solvent; for resins, the solvent can be plasticized.
solvent refined coal
   (NASA Thesaurus)
Low-sulfur distillate fuels from coal, plus the byproducts of methane, light hydrocarbons, and naphtha, all useful for making pipeline gas, ethylene, and high-octane unleaded gasoline.
solvent retention
   (NASA Thesaurus)
The occurrence of solvent residues in chemical or material end products or intermediates.
solvents
   (NASA Thesaurus)
The liquid part of an aerosol formulation used to dissolve solid or other liquid parts. Used for thinners.
sonar
   (NASA Thesaurus / NASA SP-7, 1965)
(From sound, navigation, and ranging.) A method or system, analogous to radar used under water, in which high-frequency sound waves are emitted so as to be reflected back from objects, and used to detect the objects of interest. Called asdic by the British.
sonar capsule
   (NASA SP-7, 1965)
A device designed to reflect high-frequency sound waves. See sonar.
The sonar capsule, if attached to a reentry body, may be used to locate the reentry body in case of a water landing.
sone
   (NASA SP-7, 1965)
A unit of loudness. A simple tone of frequency 1000 cycles per second, 40 decibels above a listener's threshold, produces a loudness of 1 sone.
The loudness of any sound that is judged by the listener to be n times that of the 1-sone tone is n sones. A millisone is equal to 0.001 sone. The loudness scale is a relation between loudness and level above threshold for a particular listener. In presenting data relating loudness in sones to sound pressure level, or in averaging the loudness scales of several listeners, the thresholds (measured or assumed) should be specified.
sonic
   (NASA SP-7, 1965)
1. In aerodynamics, of or pertaining to the speed of sound; that which moves at acoustic velocity as in sonic flow ; designed to operate or perform at the speed of sound, as in sonic leading edge.
2. Of or pertaining to sound, as in sonic amplifier.
In sense 2, acoustic is preferred to sonic.
sonic agglomeration
   (NASA SP-7, 1965)
The union of small particles suspended in a fluid medium into larger aggregates by the action of sound waves.
sonic barrier
   (NASA SP-7, 1965)
A popular term for the large increase in drag that acts upon an aircraft approaching acoustic velocity; the point at which the speed of sound is attained and existing subsonic and supersonic flow theories are rather indefinite. Also called sound barrier.
sonic boom
   (NASA Thesaurus / NASA SP-7, 1965)
A noise caused by a shock wave that emanates from an aircraft or other object traveling at or above sonic velocity .
A shock wave is a pressure disturbance and is received by the ear as a noise or clap.
sonic delay line
   (NASA SP-7, 1965)
= acoustic delay line.
sonic drilling
   (NASA SP-7, 1965)
The process of cutting or shaping materials with an abrasive slurry driven by a reciprocating tool attached to an electromechanical transducer operating at ultrasonic frequencies.
sonic frequency
   (NASA SP-7, 1965)
= audio frequency.
sonic soldering
   (NASA SP-7, 1965)
The method of joining metals by metallic bonding alloys through the use of mechanical vibrations to break up the surface oxides.
sonic speed
   (NASA SP-7, 1965)
Acoustic velocity; by extension, the speed of a body traveling at a Mach number of 1.
sonic wave
   (NASA SP-7, 1965)
= sound wave.
sonics
   (NASA SP-7, 1965)
The technology of sound in processing and analysis. Sonics includes the use of sound in any noncommunication process.
sophisticated
   (NASA SP-7, 1965)
Complex and intricate; making use of advanced art; requiring special skills to operate.
sorb
   (NASA SP-7, 1965)
To take up gas by sorption.
sorbate
   (NASA Thesaurus / NASA SP-7, 1965)
Gas taken up by a sorbent.
sorbent
   (NASA Thesaurus / NASA SP-7, 1965)
The material which takes up gas by sorption.
sorghum
   (NASA Thesaurus)
Any of a number of related cereal grasses with sweet juicy stalks cultivated as farm crops for grain, fodder, syrup, etc.
sorption
   (NASA Thesaurus / NASA SP-7, 1965)
The taking up of gas by absorption, adsorption, chemisorption, or any combination of these process. See absorption.
sorting algorithms
   (NASA Thesaurus)
An algorithm that finds the most significant element in a set which is then compared to each element in succession to achieve an efficient sorting process.
sound
   (NASA SP-7, 1965)
1. An oscillation in pressure, stress, particle displacement, particle velocity, etc., in a medium with internal forces (e.g., elastic, viscous), or the superposition of such propagated oscillations.
2. A sensation evoked by the oscillation described above in the human ear.
In case of possible confusion, the term sound wave or elastic wave may be used for concept 1 and the term sound sensation for concept 2. Not all sound wave can evoke an auditory sensation, e.g., ultrasound. The medium in which the sound exists is often indicated by an appropriate adjective, e.g., airborne, water borne, structure borne.
sound absorption
   (NASA SP-7, 1965)
Sound absorption is the change of sound energy into some other form, usually heat, in passing through a medium oron striking a surface.
sound barrier
   (NASA SP-7, 1965)
= sonic barrier.
sound energy
   (NASA SP-7, 1965)
The energy which sound waves contribute to a particular medium.
sound energy density
   (NASA SP-7, 1965)
At a point in a sound field, the sound energy contained in a given infinitesimal part of the medium divided by the volume of that part of the medium.
The terms instantaneous energy density, maximum energy density, and peak energy density have meanings analogous to the related terms used for sound pressure. In speaking of average energy density in general, it is necessary to distinguish between the space average (at a given instant) and the time average (at a given point).
sound energy flux
   (NASA SP-7, 1965)
The average rate of flow of sound energy for one period through any specified area.
In a medium of density rho for a plane or spherical free wave having a velocity of propagation c, the sound energy flux through the area S corresponding to an effective sound pressure p is

J equals open parens p squared S over rho c close parens cosine theta

where theta = the angle between the direction of propagation of the sound and the normal to the area S.
sound energy flux density
   (NASA SP-7, 1965)
= sound intensity.
sound field
   (NASA Thesaurus / NASA SP-7, 1965)
A region containing sound waves. See near field, far field.
sound fixing and ranging
   (NASA Thesaurus)
A method for acoustically tracking submerged bodies or floats utilizing fixed hydrophones. Used for SFAR and SOFAR.
sound generators
   (NASA Thesaurus)
Transducers which convert electrical, mechanical or other forms of energy into sound. Used for acoustic generators.
sound intensity
   (NASA Thesaurus / NASA SP-7, 1965)
In a specified direction at a point, the average rate of sound energy transmitted in the specified direction through a unit area normal to this direction at the point considered. Also called sound energy flux density, sound power density.
sound level
   (NASA SP-7, 1965)
Specifically, a weighted sound pressure level, obtained by the use of metering characteristics and the weightings A, B, or C specified in American Standard Publication Z24.3-1944: Sound Level Meters for Measurement of Noise and Other Sounds. The weighting employed pressure is 0.0002 microbar.
A suitable method of stating the weighting is, for example, The A-sound level was 43 decibels.
sound power
   (NASA SP-7, 1965)
Of a source, the total sound energy radiated by the source per unit of time.
sound power density
   (NASA SP-7, 1965)
= sound intensity.
sound pressure
   (NASA Thesaurus / NASA SP-7, 1965)
At a point, the total instantaneous pressure at that point in the presence of a sound wave minus the static pressure at that point. See effective sound pressure.
sound pressure level
   (NASA SP-7, 1965)
In decibels, 20 times the logarithm to the base 10 of the ratio of the sound pressure to the reference pressure. The reference pressure must be explicitly stated.
The following reference pressures are in common use: (a) 2 X 10E-4 microbar, (b) 1 microbar. Reference pressure (a) is in general use for measurements concerned with hearing and with sound in air and liquids, whereas (b) has gained widespread acceptance for calibration of transducers and various kinds of sound measurements in liquids. Unless otherwise explicitly stated, it is to be understood that the sound pressure is the effective (root-mean-square) sound pressure. It is to be noted that in many sound fields the sound pressure ratios are not the square roots of the corresponding power ratios.
sound probe
   (NASA SP-7, 1965)
A device that responds to some characteristic of an acoustic wave (e.g., sound pressure, particle velocity) and that can be used to explore and determine this characteristic in a sound field without appreciably altering that field.
sound wave
   (NASA Thesaurus / NASA SP-7, 1965)
A mechanical disturbance advancing with infinite velocity through an elastic medium and consisting of longitudinal displacements of the medium, i.e., consisting of compressional and rarefactional displacements parallel to the direction of advance of the disturbance; a longitudinal wave. Sound waves are small-amplitude adiabatic oscillations. The wave equation governing the motion of sound waves has the form

nabla del squared phi equals open parens one over c squared close parens open parens del squared phi over del t squared close parens

where 2 is the Laplace operator, lower case phi is the velocity potential, c is the speed of sound, and t is the time; the density variations and velocities are small. As so defined, this includes waves outside the frequency limits of human hearing, which limits customarily define sound. Also called acoustic wave, sonic wave. See ultrasonic, infrasonic, pressure wave.
Gases, liquids, and solids transmit sound waves, and the propagation velocity is characteristic of the nature and physical state of each of these media. In those cases where a steadily vibrating sound generator acts as a source of waves, one may speak of a uniform wave train; but in other cases (explosions, lightning discharges) a violent initial disturbance sends out a principal wave, followed by waves of more or less rapidly diminishing amplitude.
sounding
   (NASA Thesaurus / NASA SP-7, 1965)
1. In geophysics, any penetration of the natural environment for scientific observation.
2. In meteorology, same as upper air observation. However, a common connotation is that of a single complete radiosonde observation.
3. = air sounding.
sounding rocket
   (NASA Thesaurus)
Rockets designed primarily for routine upper air observation (as opposed to research) in the lower 250,000 feet of the atmosphere, especially that portion inaccessible to balloons, i.e., above 100,000. Used for meteorological rockets and rocket sondes.
sounding rocket
   (NASA SP-7, 1965)
A rocket that carries aloft equipment for making observations of or from the upper atmosphere. See air sounding. Compare probe, sense 3.
Usually a sounding rocket has a near vertical trajectory.
source
   (NASA SP-7, 1965)
1. The location or device from which energy emanates as a sound source, heat source , etc.
2. Specifically, in the mathematical representation of fluid flow, a hypothetical point or place from which fluid emanates.
The strength of a source; the rate of mass flow of unit density across a curve enclosing the source is given by

Q = 2pi r vr

where r is the distance from the source and vr is the radial speed.

3. Specifically, the device which supplies signal power to a transducer.
South Atlantic Anomaly
   (AS&T Dictionary)
The region over the South Atlantic Ocean where the lower Van Allen belt of energetic, electrically charged particles is particularly close to the Earth's surface. The excess energy in the particles presents a problem for satellites in orbit around the Earth.
South Tropical Disturbance
   (NASA SP-7, 1965)
An elongated dark band in the cloud surface of Jupiter at about the latitude of the Great Red Spot. It was first seen in 1901 as a dark spot which then spread rapidly. It has at times exceeded 180 degrees of longitude in length and, like the Red Spot, appears and disappears intermittently.
southbound node
   (NASA SP-7, 1965)
= descending node.
Southern sky
   (NASA Thesaurus)
That portion of the celestial sphere between the celestial equator and the celestial south pole (and generally visible from areas in the Earth's southern hemisphere).
SP (abbr)
   (NASA SP-7, 1965)
= solid propellant.
SP-100
   (Space Flight Glossary - JPL)
Space Power-100 Project developing nuclear reactors for use in space.
space
   (NASA SP-7, 1965)
1. Specifically, the part of the universe lying outside the limits of the earth's atmosphere.
2. More generally, the volume in which all celestial bodies, including the earth, move.
space based radar
   (NASA Thesaurus)
Radar systems installed on large space structures.
space biology
   (NASA SP-7, 1965)
= bioastronautics.
space capsule
   (NASA Thesaurus / NASA SP-7, 1965)
A container used for carrying out an experiment or operation in space.
A capsule is usually assumed to carry an organism or equipment.
space charge
   (NASA Thesaurus / NASA SP-7, 1965)
1. The electric charge carried by a cloud or stream of electrons or ions in a vacuum or a region of low gas pressure when the charge is sufficient to produce local changes in the potential distribution.
2. The net electric charge within a given volume.
space commercialization
   (NASA Thesaurus)
For profit activities in space or prefatory to space activity.
space communication
   (NASA Thesaurus)
The act of, or methods for, conveying information to, from, or through outer space.
space cooling (buildings)
   (NASA Thesaurus)
The cooling of buildings with a solar energy system which incorporates water chillers controlled by thermostats and other devices to provide a comfortable living environment.
space coordinates
   (NASA SP-7, 1965)
A three-dimensional system of Cartesian coordinates by which a point is located by three magnitudes indicating distance from three planes which intersect at a point.
space equivalent
   (NASA SP-7, 1965)
A condition within the earth's atmosphere that is virtually identical, in terms of a particular function, with a condition in outer space.
For example, at 50,000 feet, the drop in air pressure and the scarcity of oxygen creates a condition, so far as respiration is concerned, that is equivalent to a condition in outer space where no appreciable oxygen is present; thus, a physiological space equivalent is present in the atmosphere.
space heating (buildings)
   (NASA Thesaurus)
Heating of living areas for the comfort of occupants (human and/ or animal) by any means (electricity, fuels, solar radiation, etc.).
space imaging
   (Global Land Information System Glossary - USGS)
The U.S. Government transferred commercial sales rights of the Landsat program to the private sector on September 27, 1985, authorizing a contract with the Space Imaging. The Landsat program involves satellite remote sensing of the Earth's resources and the dissemination of that data to users worldwide. Space Imaging is a joint venture/partnership formed by Hughes Aircraft Company and RCA Corporation.
space medicine
   (NASA SP-7, 1965)
A branch of aerospace medicine concerned specifically with the health of persons who make, or expect to make, flights into space beyond the sensible atmosphere.
space modulation
   (NASA SP-7, 1965)
The combining of signals outside of an electronic device or conductor to form a signal of desired characteristics. See modulation.
space motion
   (NASA SP-7, 1965)
Motion of a celestial body through space.
That component perpendicular to the line of sight is termed proper motion and that component in the direction of the line of sight, radial motion.
space observations (from Earth)
   (NASA Thesaurus)
Surveillance of extraterrestrial phenomena from the Earth's surface.
Space Operations Center (NASA)
   (NASA Thesaurus)
A proposed NASA space station to be assembled in space that is designed for conducting space based operations such as satellite servicing, orbit transfer vehicle launch and recovery, and assembly of large space structures. Onboard capabilities could include space manufacturing and research experiments. When fully assembled it will be larger in size than the Space Shuttle.
space perception
   (NASA Thesaurus)
The ability to estimate depth or distance between points in the field of vision. Used for depth perception, distance perception, form perception, and slant perception.
space plasmas
   (NASA Thesaurus)
Concentrations of free electrons and protons in the ionosphere, plasmasphere, and beyond.
space platforms
   (NASA Thesaurus)
Gimbal-mounted platforms equipped with gyros and accelerometers for maintaining a desired orientation in inertial space independent of spacecraft motion.
space polar coordinates
   (NASA SP-7, 1965)
A system of coordinates by which a point on the surface of a sphere is located in three dimensions by (a) its distance from a fixed point at the center, called the pole; (b) the colatitude or angle between the polar axis (a reference line through the pole) and the radius vector (a straight line connecting the pole and the point); and (c) the longitude or angle between a reference plane through the polar axis and a plane through the radius vector and polar axis. See polar coordinates, spherical coordinates, cylindrical coordinates.
space probe
   (NASA SP-7, 1965)
See probe, note, and spacecraft, note and table XIV [not reproduced].
space processing
   (NASA Thesaurus)
Synthesis, processing, forming, and fabrication of compounds or materials in space or in a simulated space environment; normally involving techniques that exploit low-gravity or high-vacuum conditions.
Space Processing Applications Rocket
   (NASA Thesaurus)
Sounding rocket used for space processing experiments by NASA. Used for SPAR (rocket).
space reddening
   (NASA SP-7, 1965)
The observed reddening, or absorption of shorter wavelengths, of the light from distant celestial bodies due to scattering by small particles in interstellar space. Compare red shift.
Space Shuttle Ascent Stage
   (NASA Thesaurus)
Shuttle take-off configuration comprising the orbiter, solid rocket boosters, and external tank.
Space Shuttle Main Engine
   (NASA Thesaurus)
Liquid propellant propulsion system using fuel drawn from external tanks to provide power for the orbiter to attain orbital speed.
Space Shuttle upper stage A
   (NASA Thesaurus)
A version of a spinning solid upper stage centered around an Atlas Centaur launch vehicle. Used for SSUS-A.
Space Shuttle upper stage D
   (NASA Thesaurus)
A version of a spinning solid upper stage centered around a Delta launch vehicle. Used for SSUS-D.
Space Shuttle upper stages
   (NASA Thesaurus)
A collective term for the various types of upper stages planned for the Space Shuttle.
space simulator
   (NASA Thesaurus / NASA SP-7, 1965)
1. Any device used to simulate one or more parameters of the space environment used for testing space systems or components.
2. Specifically, a closed chamber capable of approximately the vacuum and normal environments of space.
space suit
   (NASA Thesaurus / NASA SP-7, 1965)
A pressure suit for wear in space or at very low ambient pressures within the atmosphere, designed to permit the wearer to leave the protection of a pressurized cabin.
space transportation
   (NASA Thesaurus)
The conveyance of payloads or personnel to, through, or from outer space.
space transportation system
   (NASA Thesaurus)
A joint NASA-DOD advanced space transportation concept for the 1980s. The main element of the STS is the Space Shuttle. Another element is the orbit transfer vehicles-OTV. A third element called Spacelab is designed and manufactured by the European Space Agency, has no propulsive capability and is carried by the Space Shuttle. Used for STS.
Space Transportation System flights
   (NASA Thesaurus)
Revised collective designation for all Space Shuttle flights. Used for OFT, orbital flight tests (shuttle), Space Shuttle orbital flight tests, and Space Shuttle orbital flights.
space weather
   (NASA Thesaurus)
The dynamic, highly variable conditions of the geospace environment that encompasses the sun, the interplanetary medium, and the Earth magnetosphere-ionosphere-thermosphere system. Major contributing factors include variations in the solar wind, solar flares, and solar mass ejections. Effects of space weather phenomena include performance degradation of communication, navigation, and power systems on both spacecraft and ground-based systems; and potential health hazards during extravehicular activity.
space-air vehicle
   (NASA SP-7, 1965)
A vehicle operable either within or above the sensible atmosphere. Also called aerospace vehicle.
spaceborne experiments
   (NASA Thesaurus)
A collective term designating the various experiments performed or planned in orbiting spacecraft and usually involving physical phenomena in space environments.
spacecraft
   (NASA Thesaurus / NASA SP-7, 1965)
Devices, manned and unmanned, which are designed to be placed into an orbit about the earth or into a trajectory to another celestial body.
From 1957 through 1962 spacecraft were designated by the year and a Greek letter assigned in the order of launching, as 1958 for the first satellite of 1958. When more than one object was put in orbit by a single launch vehicle, each object was numbered, as 1961o2. (Space probes were not included in this system until 1960). Beginning January 1, 1963, arabic numerals supplanted Greek letters in the scientific designations of all spacecraft with a lifetime of more than 90 minutes. Thus, the first satellite launched in 1963 was 1963-1, the last was 1963-55. When more than one component is put in orbit, alphabetical suffixes are added to the designations, as 1963-4A. The letter A usually designates the component carrying the principle scientific payload; B, C, etc., are used as needed for any subsidiary payloads and then for inert components in order of maximum brightness. The designation system was promulgated formally in the COSPAR Guide to Rocket and Satellite Information and Data Exchange. The Guide has been published in full in COSPAR Information Bulletin No. 9, July 1962, and in IGY Bulletin No. 61, July 1962. Table XIV [not reproduced] is a listing of scientific satellites and space probes launched through 1964 and is reprinted from the IG Bulletin (International Geophysics Bulletin) published by the National Academy of Sciences.
spacecraft charging
   (NASA Thesaurus)
Electric charge induction upon the surface of a spacecraft by magnetospheric plasmas or other ion sources.
spacecraft communication
   (NASA Thesaurus)
The act of, or methods for, conveying information to or from manned or unmanned spacecraft.
spacecraft defense
   (NASA Thesaurus)
The protection of spacecraft from undesirable external forces. Used for satellite defense.
spacecraft design
   (NASA Thesaurus)
The act of conceiving and planning the structure, systems, and performance characteristics of any type of spacecraft including space probes, satellites, space platforms and space stations.
spacecraft docking
   (NASA Thesaurus)
The act of coupling two or more orbiting objects; the operation of mechanically connecting together, or in some manner bring together orbital payloads. Used for docking.
spacecraft instruments
   (NASA Thesaurus)
Electronic, optical, gyroscopic, and other instruments that play a role in the control of the spacecraft, or that function to measure, record, display, or process different values or quantities encountered in the flight of a spacecraft.
spacecraft performance
   (NASA Thesaurus)
The manner or effectiveness in which any space vehicle, space platform, or space station functions while in operation in space, or in a simulated space environment.
spacecraft power supplies
   (NASA Thesaurus)
Sources of electrical energy, including batteries, generators, and energy conversion devices, that support the normal operation of spacecraft.
spacecraft propulsion
   (NASA Thesaurus)
The action or process of imparting motion to a spacecraft by means of a force such as a thrust of air or energy released by burning fuel.
spacecraft survivability
   (NASA Thesaurus)
The ability of a spacecraft to survive adverse conditions including reentry problems.
spacecraft tracking
   (NASA Thesaurus)
The process of following the movements of a spacecraft or space platform by radar, optical, or other means.
Spacelab payloads
   (NASA Thesaurus)
A general, collective term for the diverse and numerous ESA payloads planned for space experiments.
spacetennas
   (NASA Thesaurus)
The transmitting antennas of a solar power satellite transmission system which directs the high-power beam from space to a focus on the rectennas on Earth.
spacetime
   (Spacetime Wrinkles Glossary)
Space has three dimensions. However, the theory of relativity predicts that time, like space, is a dimension. In order to describe a four dimensional universe which has three spatial dimensions and one time dimension the word "spacetime" was coined. Each point in spacetime is called an event.
spalling
   (NASA Thesaurus)
Spontaneous separation of a surface layer from a metal.
span
   (NASA SP-7, 1965)
1. The dimension of a craft measured between lateral extremities; the measure of this dimension.
2. Specifically, the dimension of an airfoil from tip to tip measured in a straight line.
Span is not usually applied to vertical airfoils.
spanloader aircraft
   (NASA Thesaurus)
Advanced distributed-load cargo aircraft configurations in which the payloads are distributed across the span of the wing for a close match between aerodynamic and inertial loading for minimal bending stresses.
spark discharge
   (NASA SP-7, 1965)
That type of gaseous electrical discharge in which the charge transfer occurs intermittently along a relatively constricted path of high ion density, resulting in high luminosity. It is of short duration and to be contrasted with the nonluminous point discharge, with the diffuse corona discharge, and also with the continuous arc discharge.
The exact meaning to be attached to the term spark discharge varies somewhat in the literature. It is frequently applied to just the transient phase of the establishment of any arc discharge. A lightning discharge is a large-scale spark discharge, though its very length introduces certain details not found in laboratory short-spark processes.
spark spectrum
   (NASA SP-7, 1965)
The spectrum of an ion. The degree of ionization, or order of the spectrum, is indicated by a Roman numeral following the symbol for the element. The first spark spectrum is indicated by II, the second by III, and so on. Thus Fe IV indicates the spectrum of an iron atom which has lost three electrons. See arc spectrum.
spatial
   (NASA SP-7, 1965)
Pertaining to space.
spatial filter
   (Plasma Physics and Fusion Energy Glossary)
Device consisting of a lens pair and a pinhole aperture stop. Intensity fluctuations over the spatial extent of a laser beam are removed by passing the focused beam through the aperture stop. The pinhole must be placed in a vacuum to prevent air breakdown by the focused beam. These filters are used to counter the effects caused by self-focusing.
spatial marching
   (NASA Thesaurus)
Techniques for solving partial differential equations that move along in a space direction.
spatial resolution
   (NASA Thesaurus)
The precision with which an optical instrument can produce separable images of different points on an object.
spatio
   (NASA SP-7, 1965)
A combining form meaning space.
spatter
   (Photoglossary of Volcanic Terms - USGS)
Very fluid fragments of molten lava ejected from a vent that flatten and congeal on the ground are called spatter. Typically, spatter will build walls of solidified lava around a single vent to form a circular-shaped spatter cone or along both sides of a fissure to build a spatter rampart.
spatter and cinder cone
   (Photoglossary of Volcanic Terms - USGS)
Long-lived basaltic lava fountains that erupt spatter, scoria or cinder, and other tephra from a central vent typically build steep-sided cones called spatter-and-cinder cones. The greatest bulk of these cones consists of spatter, but during fountaining a lava flow usually pours down one side of the cone. Eruptions that build spatter and cinder cones are much longer in duration and much more varied in intensity than those that eject only spatter to build spatter cones and ramparts.
spatter rampart
   (Photoglossary of Volcanic Terms - USGS)
Lava fountains that erupt from an elongate fissure will build broad embankments of spatter, called spatter ramparts, along both sides of the fissure. The spatter commonly sticks together, or agglutinates, when it lands and is buried by later spatter. In contrast to these low linear fortifications, spatter cones are more circular and cone shaped--the only real distinction between the two structures is their shape.
special perturbations
   (NASA SP-7, 1965)
A method of orbit determination by numerical integration which takes into account the perturbing forces which are causing the orbit to depart from the orbit as calculated by Kepler laws.
specific
   (NASA SP-7, 1965)
A modifier generally implying per unit mass.
specific heat
   (NASA Thesaurus / NASA SP-7, 1965)
The ratio of the heat absorbed (or released) by unit mass of a system to the corresponding temperature rise (or fall). If this ratio varies with temperature, it must be defined as a differential quotient dQ/dT, where dQ is the infinitesimal increment of heat per unit mass and dT is the infinitesimal increment of temperature.
For gases the thermodynamic process must be specified; two specific heats are defined, one being the specific heat in a constant-pressure process

cp = (dQ/dT)p

and the other, the specific heat in a constant-volume process
cv = (dQ/dT)v

In a perfect gas these are, by definition, constants with respect to temperature, and the difference of the specific heat at constant pressure and the specific heat at constant volume is equal to the gas constant:
R = cp - cv
specific humidity
   (NASA SP-7, 1965)
In a system of moist air, the (dimensionless) ratio of the mass of water vapor to the total mass of the system. The specific humidity may be approximated by the mixing ratio for many purposes: q = w /(1 + w ) where q is the specific humidity and w is the mixing ratio. See absolute humidity, relative humidity, dew point.
specific impulse
   (NASA SP-7, 1965)
(symbol Isp )
A performance parameter of a rocket propellant, expressed in seconds, equal to the thrust F in pounds divided by the weight flow rate w dot in pounds per second:
Isp = F / w dot

Specific impulse is also equivalent to the effective exhaust velocity divided by the gravitational acceleration.
specific power
   (NASA SP-7, 1965)
The energy delivered per pound of fuel in a reactor or in a radioisotope power source.
specific propellant consumption
   (NASA SP-7, 1965)
The reciprocal of the specific impulse, i.e., the required propellant flow to produce one pound of thrust in an equivalent rocket.
specific speed
   (NASA SP-7, 1965)
Of a pump, a parameter used to predict pump performance.
specific thrust
   (NASA SP-7, 1965)
= specific impulse.
specific volume
   (NASA SP-7, 1965)
(symbol v )
Volume per unit mass of a substance. The reciprocal of density.
specifications
   (NASA Thesaurus)
Precise statements or sets of requirements to be satisfied by materials, products, systems, or services.
speckle holography
   (NASA Thesaurus)
An imaging technique whereby a speckle pattern results from laser illumination of a diffusely reflecting surface when interference occurs between the fields passing through the various portions of lens aperture. Information about the motion of an object can then be obtained from the imaged fringes resulting from the translation of two speckle patterns.
speckle interferometry
   (NASA Thesaurus)
An imaging process whereby the pattern on the image plane of an interferometer is the result of interference between two mutually coherent, but randomly speckled, fields of two, lens formed images from laser illuminated, diffusely reflecting surfaces.
spectra
   (NASA SP-7, 1965)
Plural of spectrum.
spectral
   (NASA SP-7, 1965)
1. Of or pertaining to a spectrum.
2. Referring to thermal radiation properties, for ratios such as emittance, reflectance, and transmittance, at a specified wavelength; for powers, such as emissive power, within a narrow wavelength band centered on a specified wavelength.
spectral absorptance
   (NASA SP-7, 1965)
See absorptance, note.
spectral emissivity
   (NASA SP-7, 1965)
See emissivity, note.
spectral function
   (NASA SP-7, 1965)
The Fourier representation of a given function; that is, the Fourier transform if the given function is aperiodic or the set of coefficients of the Fourier series if the given function is periodic. Also called spectrum. See continuous spectrum, discrete spectrum.
spectral line
   (Imagine the Universe Dictionary - NASA GSFC)
Light given off at a specific frequency by an atom or molecule. Every different type of atom or molecule gives off light at its own unique set of frequencies; thus, astronomers can look for gas containing a particular atom or molecule by tuning the telescope to one of its characteristic frequencies.
spectral line
   (NASA SP-7, 1965)
A bright, or dark, line found in the spectrum of some radiant source. See absorption line, emission line.
Bright lines indicate emission, dark lines indicate absorption.
spectral reflectance
   (NASA Thesaurus)
The ratio of the reflected flux to the spectrally homogeneous incident flux.
spectral sensitivity
   (NASA Thesaurus)
In electronics, radiant sensitivity considered as a function of wavelength, or in physics, the response of a device or material to monochromatic light as a function of wavelength; also known as spectral response.
spectral shift control
   (NASA Thesaurus)
Type of reactor moderator control in which the neutron spectrum is intentionally changed.
spectrograph
   (SOHO Glossary - GSFC)
An instrument that spreads light or other electromagnetic radiation into it's component wavelengths (spectrum), recording the results photographically or electronically.
spectrograph
   (NASA SP-7, 1965)
See spectroscope.
spectroheliogram
   (NASA SP-7, 1965)
See spectroheliograph.
spectroheliograph
   (NASA Thesaurus / NASA SP-7, 1965)
An instrument for taking photographs (spectroheliograms) of the image of the sun monochromatic light. The wavelength of light chosen for this purpose corresponds to one of the Fraunhofer lines, usually the light of hydrogen or ionized calcium. A similar instrument used for visual, instead of photographic, observations in a spectrohelioscope.
spectrohelioscope
   (NASA SP-7, 1965)
See spectroheliograph, note.
spectrometers
   (Galileo Project Glossary - JPL)
Instruments that measure the wavelength of electromagnetic radiation.
spectrophotometer
   (NASA SP-7, 1965)
A photometer which measures the intensity of radiation as a function of the frequency (or wavelength) of the radiation. Also called spectroradiometer. See Dobson spectrophotometer.
In one design, radiation enters the spectrophotometer through a slit and is dispersed by means of a prism. A bolometer having a fixed aperture scans the dispersed radiation so that the intensity over a narrow wave band is obtained as a function of frequency.
spectrophotovoltaics
   (NASA Thesaurus)
The enhancement of solar cell productivity by concentrating and subdividing the sunlight spectrum and focusing on specific spectrum efficient solar cells.
spectropyrheliometer
   (NASA SP-7, 1965)
An instrument which measures the spectral distribution of the intensity of direct solar radiation. See pyrheliometer, spectrophotometer.
spectroscope
   (NASA SP-7, 1965)
An apparatus to effect dispersion of radiation and visual display of the spectrum obtained.
A spectroscope with a photographic recording device is called a spectrograph.
spectroscopic binaries
   (NASA SP-7, 1965)
See binary star, note.
spectroscopy
   (Imagine the Universe Dictionary - NASA GSFC)
The study of spectral lines from different atoms and molecules. Spectroscopy is an important part of studying the chemistry that goes on in stars and in interstellar clouds.
spectrum
   (NASA SP-7, 1965)
1. In physics, any series of energies arranged according to wavelength (or frequency).
2. The series of images produced when a beam of radiant energy is subject to dispersion.
3. Short for electromagnetic spectrum or for any part of it used for a specific purpose as the radio spectrum (10 kilocycles to 300,000 megacycles).
4. In mathematics, = function.
5. In acoustics, the distribution of effective sound pressures or intensities measured as a function of frequency in specified frequency bands.
specular reflection
   (NASA Thesaurus / NASA SP-7, 1965)
Reflection in which the reflected radiation is not diffused; reflection as from a mirror. Also called regular reflection, simple reflection. Compare diffuse reflection.
The angle between the normal to the surface and the incident beam is equal to the angle between the normal to the surface and the reflected beam. Any surface irregularities on a specular reflector must be small compared to the wavelength of the incident radiation.
specular reflector
   (NASA SP-7, 1965)
Any surface exhibiting specular reflection. Also called regular reflector, simple reflector.
specular transmission density
   (NASA SP-7, 1965)
See photographic transmission density, note.
speech baseband compression
   (NASA Thesaurus)
Technique for reducing the bandwidth required to represent the human voice waveform.
speed
   (Galileo Project Glossary - JPL)
The measure of how fast an object is moving; the rate of change of position per change in time.
speed
   (NASA SP-7, 1965)
Rate of motion.
Rate of motion in a straight line is called linear speed, whereas change of direction per unit time is called angular speed. Speed and velocity are often used interchangeably although some authorities maintain that velocity should be used only for the vector quantity.
speed of light
   (Spacetime Wrinkles Glossary)
Light travels at a speed of 186,282 miles per second in vacuum from the point of view of a nearby observer. Because of the effects of general relativity the speed of light near a massive object will appear slower to a distant observer, and this effect has been confirmed in experiments. The speed of light is the theoretical limit to the speed of any particle in the universe. More fundamentally, no cause can result in an effect that requires travel faster than light.
speed of light
   (NASA SP-7, 1965)
(symbol c )
The speed of propagation of electromagnetic radiation through a perfect vacuum; a universal dimensional constant equal to 299,792.5 +/- 0.4 kilometers per second. Also called velocity of light.
speed of relative movement
   (NASA SP-7, 1965)
Also called relative speed. See relative movement.
speed of sound
   (NASA SP-7, 1965)
(symbol cs )
The speed of propagation of sound waves. In the atmosphere

c sub s equals open bracket gamma open parens R to the asterisk power over M sub zero close parens T sub M close bracket to the one half power

where gamma lower case is the ratio of specific heat of air at constant pressure to that a constant volume, R * is the universal gas constant, M0 is the mean molecular weight of air at sea level, and TM is the molecular scale temperature.
At sea level in the standard atmosphere, the speed of sound is 340.294 meters per second (1116.45 feet per second). The concept of the speed of sound in the atmosphere loses its applicability at about 90 kilometers where the mean of free path of air molecules approaches the wavelengths of sound waves.
spent fuels
   (NASA Thesaurus)
Nuclear reactor fuels irradiated to the extent that they no longer can effectively sustain a chain reaction.
sphere of influence
   (NASA SP-7, 1965)
The surface in space about a planet where the ratio of the force with which the sun perturbs the motion of a particle about the planet, to the force of attraction of the planet equals the ratio of the force with which the planet perturbs the motion of a particle about the sun, to the force of attraction of the sun on the particle.
The volume inside this surface defines the region where the attracting body exerts the primary influence on a particle.
sphere of position
   (NASA SP-7, 1965)
See line of position, note.
spherical angle
   (NASA SP-7, 1965)
The angle between two intersecting great circles.
spherical coordinates
   (NASA Thesaurus)
A system of curvilinear coordinates in which the position of a point in space is designated by its distance from the origin or pole (the radius vector), the angle phi between the radius vector and a vertically directed polar axis (the cone angle or coaltitude) and the angle theta between the plane of the phi and a fixed meridian plane through the polar axis (the polar angle or longitude). Used for curvilinear coordinates.
spherical coordinates
   (NASA SP-7, 1965)
1. A system of coordinates defining a point on a sphere or spheroid by its angular distances from a primary great circle and from a reference secondary great circle, as latitude and longitude. See celestial coordinates.
2. = space polar coordinates.
spherical excess
   (NASA SP-7, 1965)
The amount by which the sum of the three angles of a spherical triangle exceeds 180 degrees.
spherical plasmas
   (NASA Thesaurus)
Confined circular plasmas.
spherical stratification
   (NASA SP-7, 1965)
See horizontal stratification.
spherical system
   (NASA SP-7, 1965)
A trajectory measuring system, whose locus of the measured range is a sphere with the ground equipment at the center.
A unique point in space is determined by the intersection of three or more spheres. The term spherical system has been applied to systems using three or more slant ranges to determine space position.
spherical triangle
   (NASA SP-7, 1965)
A closed figure having arcs of three great circles as sides.
spherical wave
   (NASA SP-7, 1965)
A wave whose phase front surfaces are spheres. Such waves propagate from a point source.
spherics
   (NASA SP-7, 1965)
Variant spelling of sferics.
spheroid
   (NASA SP-7, 1965)
An ellipsoid; a figure resembling a sphere. Also called ellipsoid or ellipsoid of revolution from the fact that it can be formed by revolving an ellipse about one of its axes. If the shorter axis is used as the axis of revolution, an oblate spheroid results, and if the longer axis is used, a prolate spheroid results. The earth is approximately an oblate spheroid.
spheroidal excess
   (NASA SP-7, 1965)
The amount by which the sum of the three angles of a triangle on the surface of a spheroid exceeds 180 degrees.
spheroids
   (NASA Thesaurus)
Ellipsoids; figure resembling spheres.
spheromaks
   (NASA Thesaurus)
Toroidal fusion reactors.
spicules
   (NASA Thesaurus / NASA SP-7, 1965)
Bright spikes extending into the chromosphere of the sun from below.
They are several hundred miles in diameter and extend outward 5000 to 10,000 miles. Spicules have a lifetime of several minutes and may be related to granules.
spin
   (NASA SP-7, 1965)
= angular momentum (in atomic and nuclear physics).
spin axis
   (NASA SP-7, 1965)
The axis of rotation of the rotor of a gyro.
spin glass
   (NASA Thesaurus)
A magnetic alloy in which the concentration of magnetic atoms is such that below a certain temperature their magnetic moments are no longer able to fluctuate thermally in time but are still directed at random in loose analogy to the atoms of ordinary glass.
spin rocket
   (NASA SP-7, 1965)
A small rocket that imparts spin to a larger rocket vehicle or spacecraft.
spin stabilization
   (NASA Thesaurus / NASA SP-7, 1965)
Directional stability of a spacecraft obtained by the action of gyroscopic forces which result from spinning the body about its axis of symmetry.
spin table
   (NASA SP-7, 1965)
A flat round platform on which human and animal subjects can be placed in various positions and rapidly rotated, much as on a phonograph record, in order to simulate and study the effects of prolonged tumbling at high rates.
Complex types of tumbling can be simulated by mounting the spin table on the arm of a centrifuge.
spineward acceleration
   (NASA SP-7, 1965)
See physiological acceleration.
spinner
   (NASA SP-7, 1965)
Rotating part of a radar antenna used to impact any subsidiary motion in addition to the primary slewing of the beam.
spinning solid upper stage
   (NASA Thesaurus)
Space Shuttle upper stage designed for launching of satellites not requiring the full capacity of the interim upper stage; does not requires inertial guidance system nor three-axis stabilization; can handle payloads of the class now launched by Delta or Atlas/ Centaur.
spiral layer
   (NASA SP-7, 1965)
= Ekman layer.
spiral scanning
   (NASA SP-7, 1965)
Scanning in which the direction of maximum radiation describes a portion of a spiral. The rotation is always in one direction.
spoiler
   (NASA Thesaurus / NASA SP-7, 1965)
A plate, series of plates, comb, tube, bar, or other device that projects into the airstream about a body to break up or spoil the smoothness of the flow, especially such a device that projects from the upper surface of an airfoil, giving an increased drag and a decreased lift. Compare deflector, sense (a).
Spoilers are normally movable and consist of two basic types: the flap spoiler, which is hinged along one edge and lies flush with the airfoil or body when not in use, and the retractable spoiler, which retracts edgewise into the body.
spontaneous emission
   (NASA SP-7, 1965)
The decay of an atom or ion in an excited energy state Ej to a lower state Ei without the influence of any external perturbation. This process results in the emission of a photon of energy

hv = Ej - Ei

where h is the Planck constant and v is the frequency.
spontaneous-ignition temperature
   (NASA SP-7, 1965)
In testing fuels, the lowest temperature of a plate or other solid surface adequate to cause ignition in air of a fuel upon the surface.
sporadic D
   (NASA SP-7, 1965)
See ionosphere.
sporadic E
   (NASA SP-7, 1965)
See ionosphere.
sporadic meteor
   (NASA SP-7, 1965)
A meteor which is not associated with one of the regularly recurring meteor shower or streams.
spores
   (NASA Thesaurus / NASA SP-7, 1965)
The reproductive element of the lower forms of living organism, usually unicellular.
SPOT (French satellite)
   (NASA Thesaurus)
French satellite with high visible resolution for observations of the Earth. It was launched in February 1986. The acronym is derived from the French, Satellite Pour Observation de le Terre.
spray electrification
   (NASA SP-7, 1965)
= Lenard effect.
spray region
   (NASA SP-7, 1965)
= fringe region.
spread reflection
   (NASA Thesaurus / NASA SP-7, 1965)
Reflection of electromagnetic radiation from a rough surface with large irregularities. Also known as mixed reflection.
spread spectrum transmission
   (NASA Thesaurus)
Communications technique with many different signal waveforms transmitted in a wide band; power is spread thinly over the band so that narrow-band radios can operate within the band without interference.
spring (season)
   (NASA Thesaurus)
The season of the year between winter and summer. Its beginning is the vernal equinox and its end the summer solstice.
springs (water)
   (NASA Thesaurus)
Places where ground water flows naturally from rocks onto the land surface or into a body of surface water. Their occurrence depends on the nature and relationship of rocks, especially permeable and impermeable strata, on the position of the water table, and on the topography.
sprites
   (NASA Thesaurus)
[atmospheric physics] Short-lived luminosities observed at high altitudes above thunderstorms, apparently associated with upward discharges of thunderstorm electricity. They appear as columnar diffuse reddish glows between 30 km and 80 km above ground, lasting tens of milliseconds, following large positive cloud-to-ground lightning strokes.
spurious disk
   (NASA SP-7, 1965)
The round image of perceptible diameter of a star as seen through a telescope, due to diffraction of light in the telescope.
spurious emission
   (NASA SP-7, 1965)
= spurious radiation.
spurious radiation
   (NASA SP-7, 1965)
1. Any undesired emission from a radio transmitter.
2. Any electromagnetic radiation from a radio receiver. Also called spurious emission.
spurious response
   (NASA SP-7, 1965)
Output from a receiver due to a signal or signals having frequencies other than that to which the receiver is tuned.
spurious transmitter output
   (NASA SP-7, 1965)
Any part of the radio frequency output of a transmitter which is not a component of the theoretical output as determined by the type of modulation and specified bandwidth limitations.
spurious tube counts
   (NASA SP-7, 1965)
In radiation-counter tubes, counts other than background counts and those caused directly by the radiation to be measured.
Spurious counts are caused by failure of the quenching process, electrical leakage, and the like. Spurious counts may seriously affect measurement of background counts.
sputnik satellites
   (From Stargazers to Starships Glossary - GSFC)
The first artificial Earth satellite, orbited by the Soviet Union on October 7, 1957, using Korolev's R-7 rocket.
sputtering
   (NASA Thesaurus / NASA SP-7, 1965)
Dislocation of surface atoms of a material from bombardment by high-energy atomic particles.
squama
   (NASA Thesaurus)
A scale or structure resembling a scale.
square wave
   (NASA Thesaurus / NASA SP-7, 1965)
1. An oscillation, the amplitude of which shows periodic discontinuities between two values, remaining constant between jumps.
2. Specifically, in radar a pulse initiated by a rapid rise to peak power, maintained at a constant peak power over the finite pulse length, and terminated by rapid decrease from peak power.
square wells
   (NASA Thesaurus)
The impurity potential areas which bound an electron or hole in semiconducting crystals such as silicon.
squeeze casting
   (NASA Thesaurus)
The technique of working liquid metals under pressure into near net shapes; it includes the technique of forging metal compounds.
squeeze films
   (NASA Thesaurus)
Thin viscoelastic fluid films squeezed between two usually planar structures to serve as sealants, load dampers, lubricants, etc.
squeezed states (quantum theory)
   (NASA Thesaurus)
Single mode minimum uncertainty states for which the fluctuations in one quadrature phase of the field are smaller than would occur for a coherent state. Used for two photon coherent states.
squib
   (NASA Thesaurus / NASA SP-7, 1965)
1. Any of various small explosive devices.
2. An explosive device used in the ignition of a rocket. Usually called an igniter. Used for XM-6 squib and XM-8 squib.
squid (detectors)
   (NASA Thesaurus)
Superconducting quantum interference device magnetometers. Used for superconducting quantum interferometers.
squitch
   (NASA SP-7, 1965)
A squib -operated switched.
squitter
   (NASA SP-7, 1965)
Random firing, intentional or otherwise, of a transponder transmitter in the absence of interrogation.
SS loran
   (NASA SP-7, 1965)
Sky-wave synchronized loran, or loran in which the sky wave rather than the ground wave from the master controls the slave. SS loran is used with unusually long baselines.
SSA
   (Space Flight Glossary - JPL)
Solid State Amplifier in a spacecraft telecommunications subsystem, the final stage of amplification for downlink.
SSB (abbr)
   (NASA SP-7, 1965)
= single sideband.
SSI
   (Space Flight Glossary - JPL)
Solid State Imaging Subsystem, the CCD-based cameras on Galileo.
St. Elmo's fire
   (NASA SP-7, 1965)
= corona discharge.
stability
   (NASA Thesaurus / NASA SP-7, 1965)
1. The property of a body, as an aircraft or rocket, to maintain its attitude or to resist displacement, and, if displaced, to develop forces and moments tending to restore the original condition.
2. Of a fuel, the capability of a fuel to retain its characteristics in an adverse environment, e.g. extreme temperature.
stability augmentation
   (NASA Thesaurus)
Maintenance of aircraft stability in flight by means of automatic control devices which supplement a pilot's manipulation of the aircraft controls. The automatic controls are used to modify inherent aircraft handling problems.
stability augmentation system
   (NASA SP-7, 1965)
An auxiliary system to the basic manual vehicle control system whereby response of the control surfaces to inputs by the pilot can be adjusted to give a preselected vehicle response by selection of certain fixed gains in a standard feedback loop on control-surface output.
stabilized data
   (NASA SP-7, 1965)
Radar data output corrected for tilt or roll of an unstabilized radar antenna, such as shipboard installations, etc.
stable base
   (Global Land Information System Glossary - USGS)
In cartography, a stable base includes those source materials with a better likelihood for dimensional stability and longevity than paper (e.g., Mylar or film).
stable platforms
   (NASA SP-7, 1965)
A gyroscopic device so designed as to maintain a plane of reference in space regardless of the movement of the vehicle carrying the stable platform.
stadimeter
   (NASA Thesaurus / NASA SP-7, 1965)
An instrument for determining the distance to an object of know dimension by measuring the angle subtended at the observer by the object. The instrument is graduated directly in distance.
stadimetric
   (NASA SP-7, 1965)
Pertaining to a navigational fix which involves a measure of distance.
stage
   (Glossary of Hydrologic Terms - NOAA)
(gage height) The height of a water surface above an established "zero" plane, or datum.
stage
   (NASA SP-7, 1965)
1. A self-propelled separable element of a rocket vehicle. See multistage rocket.
2. A step or process through which a fluid passes, especially in compression or expansion.
3. A set of stator blades and a set of rotor blades in an axial-flow compressor or in a turbine; an impeller wheel in a radial-flow compressor. See multistage compressor, single-stage compressor, single-stage turbine.
stage-and-a-half
   (NASA SP-7, 1965)
A liquid propellant rocket of which only part of the propulsion unit falls away from the rocket vehicle during flight, as in the case of booster rockets falling away to leave the sustainer engine to consume remaining fuel.
staging
   (NASA SP-7, 1965)
The process or operation during the flight of a rocket vehicle whereby a full stage or half stage is disengaged from the remaining body and made free to decelerate or be propelled along its own flightpath. See separation.
staging (rockets)
   (From Stargazers to Starships Glossary - GSFC)
The placing of smaller rockets on top of larger ones, increasing the lifting ability of the combined set-up.
stagnation point
   (NASA Thesaurus / NASA SP-7, 1965)
A point in a field of flow about a body where the fluid particles have zero velocity with respect to the body.
stagnation pressure
   (NASA SP-7, 1965)
1. The pressure at a stagnation point.
2. In compressible flow, the pressure exhibited by a moving gas or liquid brought to zero velocity by an isentropic process.
3. = total pressure.
4. = impact pressure.
Because of the lack of a standard meaning, stagnation pressure should be defined when it is used.
stagnation region
   (NASA SP-7, 1965)
Specifically, the region at the front of a body moving through a fluid where the fluid has negligible relative velocity.
stand talker
   (NASA SP-7, 1965)
A person on a static test stand responsible for coordinating and timing the preparations for a static test.
standard
   (NASA SP-7, 1965)
1. An exact value, or a concept, that has been established by authority or agreement, to serve as a model or rule in the measurement of a quantity or in the establishment of a practice or procedure.
2. A document that establishes engineering and technical limitations and applications for items, materials, processes, methods, design, or engineering practices.
standard artillery atmosphere
   (NASA SP-7, 1965)
A set of values describing atmospheric conditions on which ballistic computations are based: namely, no wind, a surface temperature of 15 degrees C, a surface pressure of 1000 millibars, a surface relative humidity of 78 percent, and a lapse rate which yields a prescribed density-altitude relation.
standard artillery zone
   (NASA SP-7, 1965)
A vertical subdivision of the standard artillery atmosphere. It may be considered a layer of air of prescribed thickness and density.
standard atmosphere
   (NASA SP-7, 1965)
1. A hypothetical vertical distribution of atmospheric temperature, pressure, and density which, by international agreement, is taken to be representative of the atmosphere (see table XV [not reproduced]) for purposes of pressure altimeter calibrations, aircraft performance calculations, aircraft and rocket design, ballistic tables, etc. The air is assumed to be devoid of dust, moisture, and water vapor and to obey the perfect gas law and the hydrostatic equation (the air is static with respect to the earth).
Standard atmospheres, sense 1, which have been used are: (a) The NACA standard atmosphere, also called U.S. standard atmosphere, prepared in 1925, which was supplanted by (b) The ICAO standard atmosphere, adopted in 1952, which was extended to greater altitudes by (c) The ARDC model atmosphere, 1956, and (d) The U.S. extension to the ICAO standard atmosphere, adopted in 1956, which has been revised by (e) The ARDC model atmosphere, 1959, which incorporated some satellite data which has been supplanted by (f) The U.S. Standard Atmosphere-1962. (See Table XV [not reproduced]).
2. (abbr atm). A standard unit of atmospheric pressure. Defined as that pressure exerted by a 760-milimeter column of mercury at standard gravity (980.665 centimeters per second) at temperature 0o C.
1 standard atmosphere = 760 milimeters of mercury = 29.9213 inches of mercury = 1013.250 millibars
standard conditions
   (NASA SP-7, 1965)
= standard temperature and pressure.
standard deviation
   (NASA Thesaurus / NASA SP-7, 1965)
(symbol sigma )
A measure of the dispersion of data points around their mean value. It is the positive square root of the arithmetic mean of the squares of the deviation from the arithmetic mean of the population:

sigma equals square root of (summation symbol d squared m over n)

where m is arithmetic mean; d is deviation from the arithmetic mean; and n is number of points.
standard error of estimate
   (NASA SP-7, 1965)
(symbol S) A measure of the dispersion (scatter) of data points with respect to a curve of regression. S is the positive square root of the arithmetic mean of the squares of the deviations from a curve of regression:

S equals square root of (summation symbol d squared R over n)

where d is deviation from R ; R is curve of regression; and n is number of points.
S is a measure of the variation to be expected in making predictions from the regression equation.
standard gravity
   (NASA SP-7, 1965)
See gravity.
standard pressure
   (NASA SP-7, 1965)
1. In meteorology, usually a pressure of 1000 millibars, but other pressures may be used as standard for specific purposes.
2. In physics, a pressure of 1 standard atmosphere.
standard propagation
   (NASA SP-7, 1965)
The propagation of radio energy over a smooth spherical earth of uniform dielectric constant and conductivity under conditions of standard refraction in the atmosphere, i.e., an atmosphere in which the index of refraction decreases uniformly with height at a rate of 12 N-units per 1000 feet. See superstandard propagation, substandard propagation, standard atmosphere.
Standard propagation results in a ray curvature due to refection which has a value approximately one-fourth that of the earth's curvature, giving a radio horizon which is about 15 percent greater than the distance to the geometrical horizon. This is equivalent to straight-line propagation over a fictitious earth whose radius is four-thirds the radius of the actual earth.
standard refraction
   (NASA SP-7, 1965)
The refraction which would occur in an idealized atmosphere in which the index of refraction decreases uniformly with height at the rate of 39 X 10E-6 per kilometer. See standard propagation.
Standard refraction may be included in ground-wave calculations by use of an effective earth radius of 8.5 X 10E6 meters, or four-thirds the geometrical radius of the earth.
standard temperature
   (NASA SP-7, 1965)
1. A temperature that depends upon some characteristic of some substance, such as the melting, boiling, or freezing point, that is used as a reference standard of temperature.
2. In physics, usually the ice point (0 degrees C); less frequently, the temperature of maximum water density (4 degrees C).
3. In meteorology, this has no generally accepted meaning, except that it may refer to the temperature at zero altitude in the standard atmosphere (15 degrees C).
standard temperature and pressure
   (NASA SP-7, 1965)
Null
standard time
   (NASA SP-7, 1965)
See time.
standard value of gravity
   (NASA SP-7, 1965)
See acceleration of gravity.
standard-deviation estimate
   (NASA SP-7, 1965)
See standard deviation, note.
standardization
   (NASA Thesaurus / NASA SP-7, 1965)
1. The act or process of reducing something to, or comparing it with, a standard.
2. A measure of uniformity.
3. A special case of calibration whereby a known input is applied to a device or system for the purpose of verifying the output or adjusting the output to a desired level or scale factor.
Applied to transducers, standardization indicates adjustments of the output to a standard value within specified limits of error.
standardize
   (NASA SP-7, 1965)
= normalize.
standards
   (NASA Thesaurus)
References used as a basis for comparison or calibration. Concepts that have been established by authority, custom, or agreement to serve as models or rules in the measurement of quantity of the establishment of a practice or a procedure. Used for references (standards).
standing wave
   (NASA Thesaurus / NASA SP-7, 1965)
A periodic wave having a fixed distribution in space which is the result of interference of progressive waves of the same frequency and kind. Such waves are characterized by the existence of nodes or partial nodes and antinodes that are fixed in space.
Stanton number
   (NASA SP-7, 1965)
(symbol NSt ). A number expressing the ratio of the heat transmission perpendicular and parallel to the flow direction, defined as h/cprhov where h is the heat transfer coefficient, cp is the specific heat, rho is the density, and v is the flow velocity.
star
   (NASA SP-7, 1965)
1. A self-luminous celestial body exclusive of nebulas, comets, and meteors; any one of the suns seen in the heavens. Distinguished from planets or planet satellites that shine by reflected light. See navigational stars, table VII.
2. Any luminous body seen in the heavens.
The star (sense 1) of our solar system is the sun. In sense 2, star sometimes excludes the sun, the moon, and manmade satellites from the category.
star catalogue
   (NASA SP-7, 1965)
A listing of stars giving positions for a specified mean equinox and equator. Stars are often identified by catalogue numbers.
star classification
   (NASA SP-7, 1965)
Stars are classified by their spectra, designated by letters, sometimes with numerical subdivisions, as the sun is a G1-type star. The seven main types with their principal spectral characteristics are, in order of decreasing temperature:
O - He II absorption;
B - He I absorption;
A - H absorption;
F - Ca II absorption;
G - strong metallic lines;
K -bands developing;
M - very red.

Also, the letters, P, W, Q, R, N, and S are used to designate comparatively rare types of stars which do not fall into the main series.

star cluster
   (NASA Thesaurus / NASA SP-7, 1965)
A group of stars physically close together in space.
star formation
   (NASA Thesaurus)
The collapse under gravity of molecular clouds of interstellar matter to form clusters of protostars, and the continuing collapse of the protostars to form main-sequence stars.
star formation rate
   (NASA Thesaurus)
The rate at which stars are formed within a specified region or galaxy; sometimes expressed as the number of solar masses per year.
star grain
   (NASA SP-7, 1965)
= star perforated grain.
star perforated grain
   (NASA SP-7, 1965)
A hollow rocket propellant grain with the cross section of the hole having a multipointed shape.
star tracker
   (NASA Thesaurus / NASA SP-7, 1965)
A telescopic instrument on a rocket or other flight borne vehicle that locks onto a celestial body and gives guidance reference to the vehicle during flight. See celestial guidance, sun tracker.
Stardust Mission
   (NASA Thesaurus)
First U.S. mission launched to robotically obtain samples in deep space and return them to Earth. The NASA Discovery-class mission will return dust samples collected from the debris cloud surrounding the nucleus of Comet Wild 2. Interstellar dust will also be collected. The mission spacecraft takes advantage of an Earth gravity-assist maneuver to reach the comet, and uses an aerogel-based dust collector.
Stark effect
   (NASA Thesaurus / NASA SP-7, 1965)
The broadening or splitting of a spectral line observed when a luminous gas is acted upon by a strong electric field.
Starlab
   (NASA Thesaurus)
A proposed satellite ultraviolet telescope that was a joint project between the United States, Canada, and Australia. It is currently in abeyance. Used for Spacelab UV-Optical Telescope Facility.
stars
   (NASA Thesaurus)
Self-luminous celestial bodies exclusive of nebulas, comets, and meteors; suns seen in the heavens. Distinguished from planets or natural satellites that shine by reflected light.
Starsat telescope
   (NASA Thesaurus)
An anastigmatic 3-mirror reflecting telescope for ultraviolet astronomy purposes aboard the Starsat satellite.
starspots
   (NASA Thesaurus)
Temporary disturbed areas in the stellar photosphere that appear dark because they are colder than the surrounding areas.
starting pressure
   (NASA SP-7, 1965)
In rocketry, the minimum chamber pressure required to establish shock-free flow in the exit plane of a supersonic nozzle.
state of the art
   (NASA SP-7, 1965)
The level to which technology and science have at any designated cutoff time been developed in a given industry or group of industries.
state parameter
   (NASA SP-7, 1965)
= thermodynamic function of state.
state variable
   (NASA SP-7, 1965)
Any independent variable in a problem which must be specified to define a condition of state, as for example a component of position.
static
   (NASA SP-7, 1965)
1. Involving no variation with time.
2. Involving no movement, as in static test.
3. Any radio interference detectable as noise in the audio stage of a receiver.
static conversion
   (NASA SP-7, 1965)
Energy conversion in which no moving parts or equipment are utilized.
static firing
   (NASA Thesaurus / NASA SP-7, 1965)
The firing of a rocket engine in a hold-down position to measure thrust and accomplish other tests.
static models
   (NASA Thesaurus)
Sets of equations of physical laws to determine a balance of systems at rest.
static pressure
   (NASA SP-7, 1965)
(symbol p)
1. The pressure with respect to a stationary surface tangent to the mass-flow velocity vector.
2. The pressure with respect to a surface at rest in relation to the surrounding fluid.
static test
   (NASA SP-7, 1965)
An instance of static testing.
static testing
   (NASA SP-7, 1965)
The testing of a rocket or other device in a stationary or hold-down position, either to verify structural design criteria, structural integrity, and the effects of limit loads or to measure the thrust of a rocket engine.
static tube
   (AS&T Dictionary)
A device used to measure the static pressure in a stream of fluid; is made up of a perforated, tapered tube placed parallel to the flow and has a branch connected to a manometer.
station
   (NASA SP-7, 1965)
A location where measurements are made, e.g., along an airfoil in a wind tunnel test.
station constants
   (NASA SP-7, 1965)
In tracking and telemetry, constants usually associated with instrumentation sites, e.g., survey coordinates, zeroing correction, etc.
station error
   (NASA SP-7, 1965)
In geodesy and surveying, the difference, usually negligible, between the astronomical and geodetic latitude, due to local gravitational anomalies.
station keeping
   (NASA SP-7, 1965)
The sequence of maneuvers that maintains a vehicle in a predetermined orbit.
station pressure
   (NASA SP-7, 1965)
The atmospheric pressure computed for the level of the station elevation.
This may or may not be the same as either the climatological station pressure or the actual pressure, the difference being attributable to the difference in reference elevations. Station pressure usually is the base value from which sea-level pressure and altimeter setting are determined.
stationary orbit
   (NASA Thesaurus / NASA SP-7, 1965)
An orbit in which the satellite revolves about the primary at the angular rate at which the primary rotates on its axis. From the primary, the satellite thus appears to be stationary over a point on the primary.
A stationary orbit with respect to the earth is commonly called a 24-hour orbit.
stationary wave
   (NASA SP-7, 1965)
A standing wave in which the net energy flux is zero at all points.
Stationary waves can only be approximated in practice.
stationkeeping
   (NASA Thesaurus)
The sequence of maneuvers that maintains a vehicle in predetermined orbit.
statistical mechanics
   (NASA Thesaurus)
Branch of physics concerned with predictions of the behavior of macroscopic systems based on the interactions of the microscopic constituents of the system, where the number of constituents is very large.
stator
   (NASA Thesaurus / NASA SP-7, 1965)
In machinery, a part or assembly that remains stationary with respect to a rotating or moving part or assembly such as the field frame of an electric motor or generator, or the stationary casing and blades surrounding an axial-flow-compressor rotor or turbine wheel; a stator blade.
statute mile
   (NASA SP-7, 1965)
5280 feet = 1.6093 kilometers = 0.869 nautical mile. Also called land mile.
STDN (network)
   (NASA Thesaurus)
Spaceflight Tracking and Data Network. Name changed from Space Tracking and Data Acquisition Network (STDAN). Used for Satellite Tracking and Data Acq Network, Spacecraft Tracking and Data Network, and STADAN (satellite tracking network).
steady flight
   (NASA SP-7, 1965)
Flight without accelerations or oscillations.
steady flow
   (NASA SP-7, 1965)
A flow whose velocity vector components at any point in the fluid do not vary with time. See streamline flow.
steady state
   (NASA Thesaurus / NASA SP-7, 1965)
1. The condition of a substance or system whose local physical and chemical properties do not vary with time.
2. Specifically, the stable operating condition of a reactor in which the neutron inventory remains constant; that is, the effective multiplication factor ke is equal to 1.
steady-state problem
   (NASA SP-7, 1965)
See initial value problem.
steady-state vibration
   (NASA SP-7, 1965)
A condition that exists in a system if the velocity of each particle is a continuing periodic quantity.
steerable antenna
   (NASA Thesaurus / NASA SP-7, 1965)
A directional antenna whose major lobe can be readily shifted in direction.
steering function
   (NASA SP-7, 1965)
An empirical relation based on the relative distance and velocity of the target, used in guidance of rockets and spacecraft.
Stefan law
   (NASA SP-7, 1965)
= Stefan-Boltzmann law.
Stefan-Boltzmann constant
   (NASA SP-7, 1965)
(symbol sigma ). A universal constant of proportionality between the radiant emittance of a blackbody and the fourth power of the body's absolute temperature; 5.6697 X 10E-5 erg centimeter squared second degrees KE4.
Stefan-Boltzmann law
   (NASA Thesaurus / NASA SP-7, 1965)
One of the radiation laws which states that the amount of energy radiated per unit time from a unit surface area of an ideal blackbody is proportional to the fourth power of the absolute temperature of the blackbody. The law is written:

E = sigmaT4
where E is the emittance of the blackbody; sigma is the Stefan-Boltzmann constant; and T is the absolute temperature of the blackbody. Also called Stefan law.
This law was established experimentally by Stefan and was given theoretical support by thermodynamic reasoning due to Boltzmann. This law may be deduced by integrating Planck law over the entire frequency spectrum.
stellar
   (NASA SP-7, 1965)
Of or pertaining to stars.
stellar activity
   (NASA Thesaurus)
A general term encompassing stellar phenomena such as stellar flares, starspot activity, magnetic activity, nuclear fusion, etc.
stellar classification
   (High Energy Astrophysics Dictionary- GSFC)
Stars are given a designation consisting of a letter and a number according to the nature of their spectral lines which corresponds roughly to surface temperature. The classes are: O, B, A, F, G, K, and M; O stars are the hottest; M the coolest. The numbers are simply subdivisions of the major classes.
stellar classification
   (NASA SP-7, 1965)
See star classification.
stellar color
   (NASA Thesaurus)
The particular wavelengths of optical radiation emitted by a star.
stellar cores
   (NASA Thesaurus)
The central portion of the interior of stars.
stellar coronas
   (NASA Thesaurus)
Ionized regions about stars formed by x rays emitted during stellar flares. First discovery of a stellar corona was made aboard the Dutch ANS satellite (1975) when permanent x ray emission from the star SIRIUS was detected and measured.
stellar evolution
   (From Stargazers to Starships Glossary - GSFC)
The different phases in the lifetime of a star, from its formation out of gas and dust, to the time after its nuclear fuel is exhausted. Based on observations of stars at various stages of their evolution, astronomers have developed a general theory of stellar evolution, by which the Sun is a typical "main sequance" star, in the middle of its evolutionary lifespan .
stellar flares
   (NASA Thesaurus)
Ejections of material from stars in eruptions that last from a few minutes to an hour or more.
stellar inertial guidance
   (NASA SP-7, 1965)
The guidance of a flight-borne vehicle by a combination of celestial and inertial guidance; the equipment which accomplishes the guidance.
stellar interiors
   (NASA Thesaurus)
The subsurface portions of stars.
stellar magnitude
   (NASA Thesaurus)
The measure of the relative brightness of a star. Stellar magnitudes are expressed in a variety of ways, according to the method or process of observation or determination.
stellar magnitude
   (NASA SP-7, 1965)
= magnitude.
stellar map matching
   (NASA SP-7, 1965)
A process during the flight of a vehicle by which a chart of the stars set into the guidance system is automatically matched with the position of the stars observed through telescopes so as to give guidance to the vehicle. See map-matching guidance.
stellar mass accretion
   (NASA Thesaurus)
Process by which a star accumulates matter as it moves through dense clouds of interstellar gas.
stellar oscillations
   (NASA Thesaurus)
Irregular fluctuations of the stellar atmospheres.
stellar parallax
   (NASA Thesaurus)
The subtended angle at a star formed by the mean radius of the Earth's orbit; it indicates distance to a star.
stellar parallax
   (NASA SP-7, 1965)
= heliocentric parallax.
stellar physics
   (NASA Thesaurus)
A term that encompasses the physical properties of stars, such as luminosity, size, mass, density, temperature, chemical composition, evolution, activity, etc.
stellar scintillation
   (NASA SP-7, 1965)
= astronomical scintillation.
stellar systems
   (NASA Thesaurus)
Gravitationally bound groups of stars. SN (Excludes planetary systems).
stellar winds
   (High Energy Astrophysics Dictionary- GSFC)
The ejection of gas off the surface of a star. Many different types of stars, including our Sun, have stellar winds; however, a star's wind is strongest near the end of its life when it has consumed most of its fuel.
stellarator machine
   (NASA SP-7, 1965)
An experimental thermonuclear device where containment in a magnetic field is achieved by closing the field upon itself and thus allowing the particles to perform endless spiral motion.
stellarators
   (NASA Thesaurus)
Experimental thermonuclear devices where containment in a magnetic field is achieved by closing the field upon itself and thus allowing the particles to perform endless spiral motion.
step recovery diodes
   (NASA Thesaurus)
Varactors in which forward voltage injects carriers across the junction, but before the carriers can combine, the voltage reverses and carriers return to their origin in a group. The result is an abrupt cessation of reverse current and a harmonic rich waveform.
step rocket
   (NASA SP-7, 1965)
= multistage rocket.
stepping motors
   (NASA Thesaurus)
Motors whose rotations are in short and essentially uniform angular movements rather than a continuous motion.
steradian
   (Imagine the Universe Dictionary - NASA GSFC)
The supplementary SI unit of solid angle defined as the solid central angle of a sphere that encloses a surface on the sphere equal to the square of the sphere's radius.
steradian
   (NASA SP-7, 1965)
The unit solid angle which cuts unit area from the surface of a sphere of unit radius centered at the vertex of the solid angle. There are 4pi steradians in a sphere.
stereochemistry
   (NASA Thesaurus / NASA SP-7, 1965)
Chemistry dealing with the arrangement of atoms and molecules in three dimensions.
stereophonics
   (NASA Thesaurus)
The use of two sound channels to mimic normal hearing. Stereophonic satellite broadcasting has now been developed.
sternumward acceleration
   (NASA SP-7, 1965)
See physiological acceleration.
stiction
   (NASA SP-7, 1965)
= static friction.
stiffness
   (NASA Thesaurus / NASA SP-7, 1965)
The ratio of change of force (or torque) to the corresponding change in translational (or rotational) displacement of an elastic element.
stilb
   (NASA SP-7, 1965)
A unit of luminance (or brightness) equal to 1 international candle per square centimeter. Compare apostilb.
stimulated emission
   (Plasma Physics and Fusion Energy Glossary)
Radiation coherently emitted by excited ions when driven by a passing light wave and the appropriate transition wavelength. "Laser" means Light Amplification by Stimulated Emission of Radiation; it occurs when there is a population inversion between the upper and lower energy states of the transition, such that stimulated emission can dominate excitation. Stimulated emission is coherent and codirectional with the stimulating wave, and the rate of stimulated emission is proportional to the intensity of the stimulating wave.
stimulus
   (NASA SP-7, 1965)
1. = excitation.
2. = measurand.
Stirling cycle
   (NASA Thesaurus / NASA SP-7, 1965)
A theoretical heat engine cycle in which heat is added at constant volume, followed by isothermal expansion with heat addition. The heat is then rejected at constant volume, followed by isothermal compression with heat rejection.
If a regenerator is used so that heat rejected during the constant-volume process is recovered during heat addition at constant volume, the thermal efficiency of the Stirling cycle is the same as for the Carnot cycle, with less compressive work needed.
stishovite
   (NASA Thesaurus)
A mineral consisting essentially of silicon trioxide.
stochastic
   (NASA SP-7, 1965)
Conjectural; in statistical analysis, = random.
stochastic process
   (NASA Thesaurus / NASA SP-7, 1965)
An ordered set of observations in one or more dimensions, each being considered as a sample of one item from a probability distribution. Used for Poisson process.
stoichiometric
   (NASA SP-7, 1965)
Of a mixture of chemicals, having the exact proportions required for complete chemical combination, applied especially to combustible mixtures used as propellants.
stooping
   (NASA SP-7, 1965)
An atmospheric refraction phenomenon, a mirage; a special case of sinking in which the curvature of light rays due to atmospheric refraction decreases with elevation so that the visual image of a distant object is foreshortened in the vertical.
The opposite of stooping is towering.
stopping point
   (NASA SP-7, 1965)
The end of the highly luminous path of a visual meteor. Also called Hemmungspunkt.
storable
   (NASA SP-7, 1965)
Of a liquid; subject to being placed and kept in a tank without benefit of special measures for temperature or pressure control, as in storable propellant.
storage
   (NASA SP-7, 1965)
1. The act of storing information. See store.
2. Any device in which information can be stored. Also called a memory device.
3. In a computer, a section used primarily for storing information. Such a section is sometimes called a memory or a store.
The physical means of storing information may be electrostatic, ferroelectric, magnetic, acoustic, optical, chemical, electronic, electrical, mechanical, etc., in nature.
storage capacity
   (NASA SP-7, 1965)
The amount of information, usually expressed in bits (i.e., the log2 of the number of distinguishable states in which the storage can exist), that can be retained in storage. Also called memory capacity.
store
   (NASA SP-7, 1965)
1. To retain information in a device from which it can later be withdrawn.
2. To introduce information into such a device.
3. A container, rocket, bomb, or vehicle carried externally in a craft.
StormSat satellite
   (NASA Thesaurus)
A synchronous Earth-pointing satellite for severe storms studies. Used for Severe Storms Observing Satellite.
straddle carrier
   (NASA SP-7, 1965)
A ground vehicle that carries its load suspended between its wheels.
straight-line winds
   (Glossary of Weather Terms for Storm Spotters - NOAA)
Generally, any wind that is not associated with rotation, used mainly to differentiate them from tornadic winds.
strain
   (NASA SP-7, 1965)
The deformation produced by a stress divided by the original dimension.
strain gage
   (NASA Thesaurus / NASA SP-7, 1965)
An instrument used to measure the strain or distortion in a member or test specimen (such as a structural part) subjected to a force.
straits
   (NASA Thesaurus)
Relatively narrow waterways connecting two larger bodies of water.
strange attractors
   (NASA Thesaurus)
Abstract geometrical objects in theoretical physics that represent motion which is bounded but not periodic. Their detailed behavior is sensitive to external perturbations, but their overall qualitative behavior is stable. They are of particular interest in the study of turbulence.
strategic materials
   (NASA Thesaurus)
Critical raw materials whose foreign source of supply is uncertain and subject to potential cutoff. Examples of such materials are chromium, cobalt, manganese, and platinum group metals.
stratiform
   (Glossary of Weather Terms for Storm Spotters - NOAA)
Having extensive horizontal development, as opposed to the more vertical development characteristic of convection. Stratiform clouds cover large areas but show relatively little vertical development. Stratiform precipitation, in general, is relatively continuous and uniform in intensity (i.e., steady rain versus rain showers).
stratigraphy
   (NASA Thesaurus)
That branch of geology which treats of the formation, composition, sequence, and correlation of the stratified rocks as part of the Earth's crust.
stratocumulus clouds
   (Glossary of Weather Terms for Storm Spotters - NOAA)
Low-level clouds, existing in a relatively flat layer but having individual elements. Elements often are arranged in rows, bands, or waves.
stratosphere
   (NASA Thesaurus)
Region of the atmosphere between the troposphere and mesosphere, having a lower boundary about 8 km. at the poles to 15 km. at the equator and an upper boundary of about 50 km.
stratosphere
   (NASA SP-7, 1965)
See atmospheric shell.
stratosphere radiation
   (NASA Thesaurus / NASA SP-7, 1965)
Any infrared radiation involved in the complex infrared exchange continually proceeding within the stratosphere.
stratospheric warming
   (NASA Thesaurus)
A temperature rise in the global stratosphere.
stratovolcano
   (Photoglossary of Volcanic Terms - USGS)
Steep, conical volcanoes built by the eruption of viscous lava flows, tephra, and pyroclastic flows, are called stratovolcanoes. Usually constructed over a period of tens to hundreds of thousands of years, stratovolcanoes may erupt a variety of magma types, including basalt, andesite, dacite, and rhyolite. All but basalt commonly generate highly explosive eruptions. A stratovolcano typically consists of many separate vents, some of which may have erupted cinder cones and domes on the volcano's flanks. A synonym is composite cone.
stratus clouds
   (Glossary of Weather Terms for Storm Spotters - NOAA)
A low, generally gray cloud layer with a fairly uniform base. Stratus may appear in the form of ragged patches, but otherwise do not exhibit individual cloud elements as do cumulusand stratocumulus clouds. Fog usually is a surface-based form of stratus.
streak cameras
   (NASA Thesaurus)
Cameras for measuring radiation pulses by deflection of an electron beam.
streak photography
   (NASA Thesaurus)
The process of taking a time exposure photograph of a tracer particle in a fluid; the photograph reveals the motion of each tracer particle in the form of a streak which may be interpreted as a velocity vector.
stream
   (NASA SP-7, 1965)
A group of meteoroids with nearly identical orbits, also called meteor stream.
streamline
   (NASA SP-7, 1965)
A line whose tangent at any point in a fluid is parallel to the instantaneous velocity vector of the fluid at that point. The differential equations of the streamlines may be written dr X v = 0, where dr is an element of the streamline and v is the velocity vector; or in Cartesian coordinates, dx / u = dy /v = dz /w, where u, v, w, are the fluid velocities along the orthogonal X, Y, Z axes, respectively.
In steady-state flow the streamlines coincide with the trajectories of the fluid particles; otherwise, the streamline pattern changes with time. See free streamline. Compare trajectory.
streamline flow
   (NASA SP-7, 1965)
= laminar flow.
streams
   (NASA Thesaurus)
Bodies of flowing water, great or small, contained within channels as well as uncontained fluids such as air.
stress
   (NASA Thesaurus / NASA SP-7, 1965)
1. The force per unit area of a body that tends to produce a deformation.
2. The effect of a physiological, psychological, or mental load on a biological organism which causes fatigue and tends to degrade proficiency.
stress concentration
   (NASA Thesaurus / NASA SP-7, 1965)
In structures, a localized area of high stress. See stress raiser.
stress cycle
   (NASA Thesaurus / NASA SP-7, 1965)
A variation of stress with time, repeated periodically and identically. See fatigue.
stress intensity factors
   (NASA Thesaurus)
Load-induced variables in tension, compression, and/or shear which are conducive to crack initiation and propagation and fatigue fracture in materials.
stress raisers
   (NASA SP-7, 1965)
Changes in contour or discontinuities in a structure that cause local increases in stress.
stress ratio
   (NASA Thesaurus / NASA SP-7, 1965)
The ratio of the minimum stress to the maximum stress occurring in one stress cycle.
stress relaxation
   (NASA Thesaurus)
The decrease in stress after a given time at constant strain.
stress tensor
   (NASA Thesaurus / NASA SP-7, 1965)
The complete set of stress components in a solid or fluid medium, which are written as a tensor tauij. It has nine components, one for each of the coordinate faces of an imaginary element upon which the stress acts ( j = x, y, z ) and for each direction in which the stress is directed ( i = x, y, z ).
By definition, an inviscid fluid is one in which the six tangential stresses (i +/- j) are zero, and the three normal stresses (i = j) are equal to the negative of the pressure.
stress-strain relationships
   (NASA Thesaurus)
Relationship between the stress or load on a structure, structural member, or a specimen, and the strain or deformation that follows.
stretchout
   (NASA SP-7, 1965)
An action whereby the time for completing an action, especially a contract, is extended beyond the time originally programmed or contracted for.
strewn field
   (NASA SP-7, 1965)
See tektite.
striation
   (Glossary of Weather Terms for Storm Spotters - NOAA)
In Meteorology, grooves or channels in cloud formations, arranged parallel to the flow of air and therefore depicting the airflow relative to the parent cloud.
striation
   (NASA Thesaurus)
A fracture surface marking consisting of a separation of the advancing crack front into separate fracture planes.
stringer
   (NASA Thesaurus / NASA SP-7, 1965)
A slender, lightweight, lengthwise fill-in structural member in a rocket body, or the like, serving to reinforce and give shape to the skin.
Strombolian eruption
   (Photoglossary of Volcanic Terms - USGS)
Strombolian eruptions are characterized by the intermittent explosion or fountaining of basaltic lava from a single vent or crater. Each episode is caused by the release of volcanic gases, and they typically occur every few minutes or so, sometimes rhythmically and sometimes irregularly. The lava fragments generally consist of partially molten volcanic bombs that become rounded as they fly through the air.
strong interactions (field theory)
   (NASA Thesaurus)
One of the fundamental interactions of elementary particles, primarily responsible for nuclear forces and other interactions among hadrons.
strongly coupled plasmas
   (NASA Thesaurus)
Highly compressed and collisional plasmas with electron densities of order 10 to the 24th power per cubic centimeter or more. The mean kinetic and potential energies of particles in the plasma are typically of the same order of magnitude.
Strouhal number
   (NASA Thesaurus / NASA SP-7, 1965)
(symbol NStr) A nondimensional number occurring in the study of periodic or quasiperiodic variations in the wake of objects immersed in a fluid stream:

NStr = nl/u

where n is a frequency; l is a representative length, and u is a representative velocity of the stream.
structural weight
   (NASA SP-7, 1965)
= construction weight.
structured grids (mathematics)
   (NASA Thesaurus)
In computational fluid dynamics, grid systems where the flowfield is discretized into quadrilateral elements for two-dimensional fields, and hexahedral elements for three-dimensional fields. In this type of grid system the grid points can be associated with grid lines in an ordered manner.
STS
   (Space Flight Glossary - JPL)
Space Transportation System (Space Shuttle).
subassembly
   (NASA Thesaurus / NASA SP-7, 1965)
An assembly that is a component part of a larger assembly.
subastral point
   (NASA SP-7, 1965)
= substellar point.
subatomic particle
   (NASA SP-7, 1965)
Any particle of less than atomic mass, e.g., the electron, proton, and neutron, also called atomic particle.
Subatomic particles are classified by relative mass into four groups: leptons, mesons, nucleons, and hyperons, from lowest to highest masses, respectively.
subaudio frequency
   (NASA SP-7, 1965)
A frequency below the audio frequency range, below about 15 cycles per second.
subcarrier
   (Space Flight Glossary - JPL)
Modulation applied to a carrier which is itself modulated with information-carrying variations.
subcarrier
   (NASA SP-7, 1965)
A carrier which is applied as a modulating wave to modulate another carrier or an intermediate subcarrier.
subcarrier oscillator
   (NASA SP-7, 1965)
In a telemetry system, the oscillator which is directly modulated by the measurand or by the equivalent of the measurand in terms of changes in the transfer elements of a transducer.
subchannel
   (NASA SP-7, 1965)
In a telemetry system, the route required to convey the magnitude of a single subcommutated measurand.
subcommutation
   (NASA SP-7, 1965)
In telemetry, commutation of additional channels with output applied to individual channels of the primary commutator.
Subcommutation is called synchronous if its rate is a submultiple of that of the primary commutator. Unique identification must be provided for the subcommutation frame pulse.
subcontracts
   (NASA Thesaurus)
Any contracts, other than prime contracts, entered into by a prime contractor or subcontractor calling for supplies or services required for the performance of any one or more prime contracts.
subcritical flow
   (NASA Thesaurus)
Open channel flow having a low velocity and a Founde number less than unity (also described as tranquil or streaming flow).
subduction (geology)
   (NASA Thesaurus)
Descent of one tectonic unit under another. Most commonly used for descent of a slab of lithosphere, but appropriate at any scale.
subduction zone
   (Galileo Project Glossary - JPL)
A place on the surface of the Earth where two plates move toward each other, and the oceanic plate plunges beneath the other tectonic plate.
subframe
   (NASA SP-7, 1965)
In telemetry, a complete sequence of frames during which all subchannels of a specific channel are sampled once.
subgiant stars
   (NASA Thesaurus)
Celestial bodies whose position on the Hertzsprung-Russell (H-R) diagram is intermediate between that of the main-sequence stars and normal giants of the same spectral type.
subgravity
   (NASA SP-7, 1965)
A condition in which the acceleration acting on a body is less than normal gravity, between 0 and 1 g.
subharmonic
   (NASA SP-7, 1965)
A sinusoidal quantity having a frequency that is an integral submultiple of the fundamental frequency of a periodic quantity to which it is related.
sublimation
   (NASA Thesaurus / NASA SP-7, 1965)
The transmission of a substance directly from the solid state to the vapor state, or vice versa, without passing through the intermediate liquid state. See condensation, evaporation.
subliming ablator
   (NASA SP-7, 1965)
An ablation material characterized by sublimation of the material at the heated surface.
sublunar point
   (NASA SP-7, 1965)
The geographical position of the moon; that point on the earth at which the moon is in the zenith at a specified time.
submarines
   (NASA Thesaurus)
Any self-powered underwater craft or towed underwater barges and arrays.
subpermanent magnetism
   (NASA SP-7, 1965)
= permanent magnetism.
The expression subpermanent magnetism is sometimes used because of the slow dissipation of such magnetism, but the expression permanent magnetism is considered preferable.
subrefraction
   (NASA SP-7, 1965)
Less-than-normal refraction, particularly as related to atmospheric refraction.
Greater-than-normal refraction is called super refraction.
subroutine
   (NASA Thesaurus / NASA SP-7, 1965)
A set of instructions necessary to direct a computer to carry out a well-defined mathematical or logical operation; a submit of a routine, usually coded in such a manner that it can be treated as a black box by the routine using it.
subsatellite point
   (NASA SP-7, 1965)
Intersection of the local vertical passing through a satellite in orbit with the earth's surface.
subsidence
   (AS&T Dictionary)
Sinking, falling or flattening out to a lower or normal level. In Meteorology, refers to a sinking (downward) motion in the atmosphere, usually with the implication that the condition extends over a broad area. In Mining Engineering, refers to the settling of the earth's crust as a result of excavation.
subsolar
   (Galileo Project Glossary - JPL)
The point on a body that is directly beneath the Sun. The Sun's rays will hit this point at 90° to the surface.
subsolar point
   (NASA SP-7, 1965)
The geographical position of the sun; that point on the earth at which the sun is in the zenith at a specified time.
subsonic
   (NASA SP-7, 1965)
In aerodynamics, of or pertaining to, or dealing with speeds less than acoustic velocity as in subsonic aerodynamics.
subsonic flow
   (NASA Thesaurus / NASA SP-7, 1965)
Flow of a fluid, as air over an airfoil, at speeds less than acoustic velocity.
Aerodynamic problems of subsonic flow are treated with the assumption that air acts as an incompressible fluid.
substandard propagation
   (NASA SP-7, 1965)
The propagation of radio energy under conditions of substandard refraction in the atmosphere, that is, refraction by an atmosphere or section of the atmosphere in which the index of refraction decreases with height at a rate of less than 12 N-units per 1000 feet. See standard propagation, superstandard propagation.
Substandard propagation produces a less-than-normal downward bending or even an upward bending of radio waves as they travel through the atmosphere, giving closer radio horizons and decreased radar and radio coverage. It results primarily when propagation takes place through a layer in which moisture remains constant or increases with height.
substandard refraction
   (NASA SP-7, 1965)
Also called subrefraction. See substandard propagation.
substantial derivative
   (NASA SP-7, 1965)
= individual derivative.
substellar point
   (NASA SP-7, 1965)
The geographical position of a star; that point on the earth at which the star is in the zenith at a specified time. Also called subastral point.
substorm
   (Earth's Magnetosphere Glossary - GSFC)
A process by which plasma in the magnetotail becomes energized at a fast rate, flowing earthward and producing bright auroras and large Birkeland currents, for typical durations of half an hour.
substratosphere
   (NASA SP-7, 1965)
Loosely and nontechnically, the very high troposphere.
subtend
   (NASA SP-7, 1965)
To be opposite, as an arc of a circle subtends an angle at the center of the circle , the angle being formed by the radii joining the ends of the arc with the center.
sudden ionospheric disturbances
   (NASA Thesaurus)
Complex combinations of sudden changes in the conditions of the ionosphere and the effects of these changes. Used for geomagnetic crotchets and SID (ionospheric disturbances).
sudden-commencement magnetic storm
   (NASA SP-7, 1965)
A magnetic storm characterized by a world-wide sudden commencement which takes place in a matter of minutes and shows no recurrence after 27 days, the period of rotation of the sun.
sulcus
   (Galileo Project Glossary - JPL)
A complex area of subparallel furrows and ridges.
sulfation
   (NASA Thesaurus)
The introduction into an organic molecule of the sulfuric ester group (or its salts) -O-SO3H, where the sulfur is linked through an oxygen atom to the parent molecule.
sulfidation
   (NASA Thesaurus)
The reaction of a metal or alloy with a sulfur-containing species to produce a sulfur compound that forms on or beneath the surface of the metal or alloy.
SUMER
   (SOHO Glossary - GSFC)
See Solar Ultraviolet Measurements of Emitted Radiation.
summer solstice
   (NASA SP-7, 1965)
1. That point on the ecliptic occupied by the sun at maximum northerly declination. Sometimes called June solstice, first point of Cancer.
2. That instant at which the sun reaches the point of maximum northerly declination, about June 21.
sun
   (NASA Thesaurus / NASA SP-7, 1965)
The star at the center of the solar system, around which the planets, planetoids, and comets revolve. It is a G-type star.
The sun visible in the sky is called apparent or true sun. A fictitious sun conceived to move eastward along the celestial equator at a rate that provides a uniform measure of time equal to the average apparent time is called mean sun; a fictitious sun conceived to move eastward along the ecliptic at the average rate of the apparent sun is called dynamical mean sun.
sun tracker
   (NASA SP-7, 1965)
A species of star tracker designed to lock onto the sun to afford guidance to a rocket or other flight-borne object. See star tracker.
sun's way
   (NASA SP-7, 1965)
The path of the solar system through space. See solar apex.
sunflowers
   (NASA Thesaurus)
Any of a number of tall related plants having yellow, daisylike flowers with yellow, brown, purple, or almost black disks containing seeds from which an oil is extracted.
sunrise
   (NASA Thesaurus / NASA SP-7, 1965)
The crossing of the visible horizon by the upper limb of the ascending sun.
sunset
   (NASA Thesaurus / NASA SP-7, 1965)
The crossing of the visible horizon by the upper limb of the descending sun.
sunspot
   (NASA Thesaurus / NASA SP-7, 1965)
A relatively dark area on the surface of the sun consisting of a dark central umbra surrounded by a penumbra which is intermediate in brightness between the umbra and the surrounding photosphere. See relative sunspot number.
Sunspots usually occur in pairs with opposite magnetic polarities. They have a lifetime ranging from a few days to several months. Their occurrence exhibits approximately an 11-year period (the sunspot cycle).
sunspot cycle
   (NASA Thesaurus / NASA SP-7, 1965)
A cycle with an average length of 11.1 years but varying between about 7 and 17 years in the number and area of sunspots, as given by the relative sunspot number. This number rises from a minimum of 0 to 10 to a maximum of 50 to 140 about 4 years later, and then declines more slowly.
An approximate 11-year cycle has been found or suggested in geomagnetism, frequency of aurora, and other ionospheric characteristics. The u-index of geomagnetic intensity variation shows one of the strongest known correlations to solar activity. Eleven-year cycles have been suggested for various tropospheric phenomena, but none of these has been substantiated.
sunspot number
   (NASA SP-7, 1965)
See relative sunspot number.
sunspot relative number
   (NASA SP-7, 1965)
= relative sunspot number.
super high frequency
   (NASA SP-7, 1965)
(abbr SHF).
See frequency band.
superadiabatic lapse rate
   (NASA SP-7, 1965)
An environmental lapse rate greater than the dry-adiabatic lapse rate, such that potential temperature decreases with height.
superalloy
   (NASA SP-7, 1965)
An alloy developed for very high temperature service where relatively high stresses (tensile, thermal, vibratory, and shock) are encountered and where oxidation resistance is frequently required.
supercells
   (Glossary of Weather Terms for Storm Spotters - NOAA)
A thunderstorm with a persistent rotating updraft. Supercells are rare, but are responsible for a remarkably high percentage of severe weather events - especially tornadoes, extremely large hail and damaging straight-line winds.
supercommutation
   (NASA SP-7, 1965)
Commutation by connection of single data input source to equally spaced contacts of the commutator (cross-patching).
Corresponding crosspatching is required at the decommutator.
supercomputers
   (NASA Thesaurus)
Computers with very large capacity and very high speed.
superconductivity
   (NASA Thesaurus)
A property of many elements, alloys, and compounds by virtue of which their electrical resistivity vanishes and they become strongly diamagnetic under appropriate conditions. Used for Meissner effect.
superconductors (materials)
   (NASA Thesaurus)
Materials that exhibit superconductivity under appropriate conditions.
superhybrid materials
   (NASA Thesaurus)
Composites of polymers, boron-aluminum, and titanium.
superior conjunction
   (Space Flight Glossary - JPL)
Alignment between Earth and a planet on the far side of the sun.
superior conjunction
   (NASA SP-7, 1965)
The conjunction of a planet and the sun when the sun is between the earth and the other planet.
superior mirage
   (NASA SP-7, 1965)
A spurious image of an object formed above its true position by abnormal atmospheric refraction conditions; opposite to an inferior mirage. Compare towering, looming, inferior mirage.
Superior mirages occur when the temperature lapse rate near the earth's surface is less than its normal value or, especially, when the temperature actually increases with height. Under these conditions the velocity of light increases upward in such a way that light rays are bent downward as they propagate through the layer in quasi-horizontal directions. The downward curvature gives the impression that the position of the object viewed is well above its true position in space. The object also appears inverted. Complex combination of superior and inferior mirages may occur with unusual density stratifications.
superior planets
   (NASA SP-7, 1965)
The planets with orbits larger than that of the earth: Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto.
superior transit
   (NASA SP-7, 1965)
= upper transit.
superlattices
   (NASA Thesaurus)
Crystals grown by depositing semiconductors in layers whose thickness is measured in atoms.
supermassive stars
   (NASA Thesaurus)
Stars with masses exceeding about 50 times that of the sun.
supernova
   (Spacetime Wrinkles Glossary)
an exploding star. Such an explosion occurs in our galaxy at a rate of about one every 30 years. Its causes are not precisely known, but the violent movement of matter within the star may produce a significant amount of gravitational radiation. It is thought that supernovae produce pulsars.
supernovae
   (From Stargazers to Starships Glossary - GSFC)
When a star burns up all its fuel, it collapses and the released gravitational energy blows off its top layers, creating a supernova explosion. What remains of the star depends on its mass. Low-mass stars crush their atoms and become white dwarfs, about as big as Earth.
superpressure balloon
   (NASA SP-7, 1965)
See constant-level balloon, note.
superpressure balloons
   (NASA Thesaurus)
Meteorological balloons consisting of nonextensible envelopes designed to withstand higher internal pressure differentials than external ones. Such balloons will maintain constant elevations until sufficient gas diffuses from them to cause a change in buoyancy. Used for constant volume balloons and tetroons.
superrefraction
   (NASA SP-7, 1965)
= superstandard refraction.
superrotation
   (NASA Thesaurus)
The generally more rapid relative motions found in the very tenuous regions of the atmosphere at heights around 300 km. The density of the atmosphere decreases rapidly with height and more than 95 percent of the mass of the atmosphere is contained within the troposphere and lower stratosphere. These regions of the atmosphere rotate faster on average than the underlying solid Earth.
supersonic
   (NASA SP-7, 1965)
Of or pertaining to, or dealing with, speeds greater than the acoustic velocity. Compare with ultrasonic.
supersonic compressor
   (NASA Thesaurus / NASA SP-7, 1965)
A compressor in which a supersonic velocity is imparted to the fluid relative to the rotor blades, the stator blades, or to both the rotor and stator blades, producing oblique shock waves over the blades to obtain a high pressure rise.
supersonic diffusers
   (NASA Thesaurus)
Diffusers designed to reduce the velocity and increase the pressure of fluid moving at supersonic velocities.
supersonic flow
   (NASA Thesaurus / NASA SP-7, 1965)
In aerodynamics, flow of a fluid over a body at speeds greater than the acoustic velocity and in which the shock waves start at the surface of the body. Compare hypersonic flow.
supersonic nozzle
   (NASA Thesaurus / NASA SP-7, 1965)
A converging-diverging nozzle designed to accelerate a fluid to supersonic speed.
supersonics
   (NASA Thesaurus / NASA SP-7, 1965)
Specifically, the study of aerodynamics of supersonic speeds. See hypersonics.
superstandard propagation
   (NASA SP-7, 1965)
The propagation of radio waves under conditions of superstandard refraction (superrefraction) in the atmosphere, that is, refraction by an atmosphere or section of the atmosphere in which the index of refraction decreases with height at a rate of greater than 12 N-units per 1000 feet. See standard propagation, substandard propagation.
Superstandard propagation produces a greater-than-normal downward bending of radio waves as they travel through the atmosphere, giving extended radio horizons and increased radar coverage. It results primarily from propagation through layers near the earth's surface in which the moisture lapse rate is greater than normal, or the temperature lapse rate less than normal, or both. A condition in which warn dry air moves out over a cool water surface is an example of superrefraction. A layer in which the downward bending is greater than the curvature of the earth is called a radio duct. Frequently, the general term, anomalous propagation, is used for superstandard propagation.
superstandard refraction
   (NASA SP-7, 1965)
Refraction by an atmosphere or section of the atmosphere in which the index of refraction decreases with height at a rate greater than 12 N-units per 1000 feet. Also called superrefraction.
supplement
   (NASA SP-7, 1965)
An angle equal to 180 degrees minus a given angle. Thus 110 degrees is the supplement of 70 degrees and the two are said to be supplementary. See complement, explement.
supplementary angles
   (NASA SP-7, 1965)
Two angles whose sum is 180 degrees.
support equipment
   (NASA SP-7, 1965)
See ground support equipment.
surface
   (NASA SP-7, 1965)
1. A two-dimensional extent; the outside or superficies of any body; especially, the surface of the earth, either land or water, used in combinations as surface-to-air, etc.
2. A wing, rudder, propeller blade, vane, hydrofoil, or the like - applied in this sense to the entire structure or body.
surface boundary layer
   (NASA SP-7, 1965)
That thin layer of air adjacent to the earth's surface, extending up to the so-called anamometer level (the base of the Ekman layer ). Within this layer the wind distribution is determined largely by the vertical temperature gradient and the nature and contours of the underlying surface; shearing stresses are approximate constant. Also called surface layer, friction layer, atmospheric boundary layer, ground layer. See logarithmic velocity profile, planetary boundary layer, free atmosphere.
surface duct
   (NASA SP-7, 1965)
An atmospheric duct for which the lower boundary is the surface of the earth.
surface effect ships
   (NASA Thesaurus)
Vessels using ground effect principle and having submerged rigid sidewalls (sealants). Used for SES.
surface layer
   (NASA SP-7, 1965)
= surface boundary layer.
surface of position
   (NASA SP-7, 1965)
A surface on some point of which a craft is located. See line of position, fix.
surface plot
   (Solar Physics Glossary - NASA GSFC)
A three-dimensional plot mapping the intensity of radiation from a region as a distorted surface. More intense radiation is represented by higher points on the surface. Therefore, regions of intense radiation resemble mountains on the earth.
surface roughness
   (NASA Thesaurus)
The deviation of the topography of an actual surface from an ideal atomically smooth and planar surface.
surface water
   (NASA Thesaurus)
All the waters on the surface of the Earth including fresh and salt water, ice and snow.
surfactants
   (NASA Thesaurus)
A material that improves the emulsifying, dispersing, wetting, or other surface-modifying properties of liquids. Used for surface-active agents.
surge
   (NASA Thesaurus / NASA SP-7, 1965)
A transient rise in power, pressure, etc., such as a brief rise in the discharge pressure of a rotary compressor.
survey
   (NASA SP-7, 1965)
The process of determining accurately the position, extent, contour, etc., of an area, usually for the purpose of preparing a chart.
suspended phase
   (NASA SP-7, 1965)
See suspension.
suspension
   (NASA SP-7, 1965)
In physical chemistry, a system composed of one substance (suspended phase, suspensoid) dispersed throughout another substance (suspending phase) in a moderately finely divided state, but not so finely divided as to acquire the stability of a colloidal system.
Given sufficient time, a suspension will, be definition, separate itself by gravitational action into two visibly distinct portions, whereas a colloidal system, by definition, is stable. Dust in the atmosphere is an example of a suspension of a solid in a gas.
suspensions
   (NASA Thesaurus)
A two-phase system consisting of a finely divided solid dispersed in a solid, liquid, or gas.
suspensoid
   (NASA SP-7, 1965)
See suspension.
sustainer
   (NASA SP-7, 1965)
Anything that acts to sustain an action or movement already begun; specifically, a sustainer engine.
sustainer engine
   (NASA SP-7, 1965)
A rocket engine that maintains the velocity of a rocket vehicle once it has achieved its programmed velocity by use of booster or other engine.
This term is applied, for example, to the remaining engine of the Atlas after the two booster engines have been jettisoned. The term is also applied to a rocket engine used on an orbital flider to provide the small amount of thrust now and then required to compensate for the drag imparted by air particles in the upper atmosphere.
sustainer rocket engines
   (NASA Thesaurus)
Rocket engines that maintain the velocity of the rocket once it has achieved its programmed velocity by use of boosters or other engines.
SWAN
   (SOHO Glossary - GSFC)
See Solar Wind Anisotropies
SWATH (ship)
   (NASA Thesaurus)
Small waterplane area twin hull concept extension of hydrofoils for improving seaworthiness and speed. Used for Small Waterplane Area Twin Hull.
swath width
   (NASA Thesaurus)
The width of the area covered by an imaging sensor determined by the geometry of the instrument.
sweat cooling
   (NASA Thesaurus / NASA SP-7, 1965)
= transpiration cooling.
sweep
   (NASA SP-7, 1965)
The motion of the visible dot across the face of a cathode-ray tube, as a result of deflections of the electron beam.
A linear time-base sweep has a constant sweep speed before retrace. An expanded time-base sweep is produced if the sweep speeds is increased during a selected part of the cycle; a delayed time-base sweep if the start of the sweep is delayed, usually to provide an expanded scale for a particular part. A sweep intended primarily for measurement of range may be called a range sweep. See trace.
sweepback
   (From Stargazers to Starships Glossary - GSFC)
The angle by which the wing of an airplane is swept back, measured from the direction perpendicular to the fuselage.
SWG
   (Space Flight Glossary - JPL)
Science Working Group.
swing-around trajectory
   (NASA SP-7, 1965)
A planetary round trip trajectory which requires no propulsion at the destination planet, but uses the planet's gravitational field to effect the necessary orbit change to return to earth.
symbiosis
   (NASA Thesaurus)
The intimate living together of two organisms of different species, for mutual benefit.
symmetry axis
   (Plasma Physics and Fusion Energy Glossary)
The straight line (usually vertical) through the center of a configuration, when the configuration is symmetric to all (axisymmetric, like the tokamak) or some (periodic, like the stellarator) rotations about this line. Usually the z-axis.
synchrocyclotron
   (NASA SP-7, 1965)
A cyclotron in which the frequency of the electric field is frequency modulated to permit the acceleration of particles to relativistic energies. Also called FM cyclotron.
synchronism
   (NASA Thesaurus / NASA SP-7, 1965)
The relationship between two or more periodic quantities of the same frequency when the phase difference between them is zero or constant at a predetermined value.
synchronous
   (NASA SP-7, 1965)
Coincident in time, phase, rate, etc.
synchronous computer
   (NASA SP-7, 1965)
A computer in which the starting time of every ordinary operational cycle is controlled by signals which occur at regular intervals. Contrast with asynchronous computer.
synchronous orbit
   (From Stargazers to Starships Glossary - GSFC)
The circular orbit above the equator at a distance of 6.6 Earth radii, in which a spacecraft has an orbital period of 24 hours. Such satellites stay above the same spot on Earth and are therefore ideally suited for transmitting communications and broadcasts.
synchronous platforms
   (NASA Thesaurus)
Space platforms whose rotation is synchronized with that of Earth. Used for geostationary platforms.
synchronous rotation
   (High Energy Astrophysics Dictionary- GSFC)
Said of a satellite if the period of its rotation about its axis is the same as the period of its orbit around its primary. This implies that the satellite always keeps the same hemisphere facing its primary (e.g. the Moon). It also implies that one hemisphere (the leading hemisphere) always faces in the direction of the satellite's motion while the other (trailing) one always faces backward.
synchronous satellite
   (NASA Thesaurus / NASA SP-7, 1965)
An equatorial west-to-east satellite orbiting the earth at an altitude of approximately 35,900 kilometers at which altitude it makes one revolution in 24 hours, synchronous with the earth's rotation.
synchrotron
   (NASA Thesaurus / NASA SP-7, 1965)
A device for accelerating particles, ordinarily electrons, in a circular orbit in an increasing magnetic field by means of an alternating electric field applied in synchronism with the orbital motion.
synchrotron radiation
   (Imagine the Universe Dictionary - NASA GSFC)
Electromagnetic radiation given off when very high energy electrons encounter magnetic fields.
SYNCOM 4 satellite
   (NASA Thesaurus)
A geosynchronous communications satellite that was deployed on Space Shuttle STS 51A in November 1984.
synergic ascent
   (NASA SP-7, 1965)
The ascent of a rocket vehicle along a synergic curve.
synergic curve
   (NASA SP-7, 1965)
A curve plotted for the ascent of a rocket vehicle calculated to give the vehicle an optimum economy in fuel with an optimum velocity.
This curve, plotted to minimize air resistance, starts off vertically, but bends towards the horizontal between 20 and 60 miles altitude to minimize the thrust required for vertical ascent.
synodic period
   (NASA SP-7, 1965)
The interval of time between and planetary configuration of a celestial body, with respect to the sun, and the next successive same configuration of that body, as from inferior conjunction to inferior conjunction.
synodic satellite
   (NASA SP-7, 1965)
A hypothetical earth satellite, situated 0.84 of the distance to the moon on a line joining the centers of the earth and moon and having the same period of revolution as the moon.
synodical month
   (NASA SP-7, 1965)
The average period of revolution of the moon about the earth with respect to the sun, a period of 29 days 12 hours 44 minutes 2.8 seconds.
This is sometimes called the month of the phases, since it extends from new moon to the next new moon. Also called lunation.
synoptic
   (NASA SP-7, 1965)
Pertaining to or affording an overall view.
In meteorology, this term refers to meteorological data obtained simultaneously over a wide area for the purpose of presenting a comprehensive and nearly instantaneous picture of the state of the atmosphere. Thus, to a meteorologist, synoptic takes on the additional connotation of simultaneity.
synoptic correlation
   (NASA SP-7, 1965)
= Eulerian correlation.
synoptic meteorology
   (NASA Thesaurus / NASA SP-7, 1965)
The study and analysis of weather information gathered at the same time. See synoptic.
syntectic alloys
   (NASA Thesaurus)
Metallic composite materials characterized by a reversible convertibility of their solid phases into two liquid phases by the application of heat.
synthesis (chemistry)
   (NASA Thesaurus)
The application of chemical reactions to obtain desired chemical products.
synthetic aperture radar
   (NASA Thesaurus)
Active microwave sensors providing all-weather, high resolution imagery. Used for imaging radar.
synthetic apertures
   (NASA Thesaurus)
In radar technology, the simulations of large antennas by correcting the phase and magnitude of the return signals from smaller antennas, permitting the use of lower frequencies for airborne radars.
synthetic food
   (NASA Thesaurus)
Mixture of roughage, vitamins, minerals, etc., closely approximating natural foods in appearance, taste, and nutrition.
synthetic metals
   (NASA Thesaurus)
Materials which do not occur in nature but have the appearance and physical properties of true metals.
syntony
   (NASA Thesaurus / NASA SP-7, 1965)
The situation of two or more oscillating circuits having the same resonance frequency.
system
   (NASA SP-7, 1965)
1. Any organized arrangement in which each component part acts, reacts, or interacts in accordance with an overall design inherent in the arrangement.
2. Specifically, a major component of a given vehicle such as a propulsion system or a guidance system. Usually called a major system to distinguish it from the systems subordinate or auxiliary to it.
The system of sense 1 may become organized by a process of evolution, as in the solar system, or by deliberate action imposed by the designer, as in a missile system or an electrical system. In sense 2, the system embraces all its own subsystems including checkout equipment, servicing equipment, and associated technicians and attendants. When the term is preceded by such designating nouns as propulsion or guidance, it clearly refers to a major component of the missile. Without the designating noun, the term may become ambiguous. When modified by the word major, however, it loses its ambiguity and refers to a major component of the missile.
system generated electromagnetic pulses
   (NASA Thesaurus)
Electromagnetic fields generated by the emission of a large electronic current from a metallic body in space caused by the incidence on its surface of strong ionizing radiation pulses (usually x ray) from space. Used for SGEMP.
system identification
   (NASA Thesaurus)
The technology of modeling plants and processes from their dynamic response.
system of astronomical constants
   (NASA SP-7, 1965)
An interrelated group of values constituting a model of the earth and the motions which together with the theory of celestial mechanics serves for the calculations of ephemerides. See astronomical constants, note and tables II and III.
systematic error
   (NASA Thesaurus)
Non-random and often predictable error due to some physical law or caused by flaws in a measurement process.
systematic error
   (NASA SP-7, 1965)
An error that is always a function of the magnitude of the quantity observed.
When the error is constant it is called a bias error. Systematic errors are often caused by false elements in an instrument. An example is an eccentrically mounted azimuth circle or an azimuth circle with graduation errors.
systems engineering
   (NASA Thesaurus)
The process of applying science and technology to the study and planning of a system so that the relationships of various parts of the system and the use of various subsystems are fully established before designs are committed.
systems integration
   (NASA Thesaurus)
The combining of subsystems each with numerous interfaces for the input and output of data and each with specified functions vital to the planned success of the main system.
systems simulation
   (NASA Thesaurus)
The simulation of any dynamic system.
syzygy
   (NASA SP-7, 1965)
A point of the orbit or a planet or satellite at which it is in conjunction or opposition.
The term is used chiefly in connection with the moon, when it refers to the points occupied by the moon at new and full phase.