Aerospace Science and Technology Dictionary S Page

Aerospace Science
&
Technology Dictionary

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 AB, read A dot B, and occasionally as (AB). If the vectors A and B have the components A_x, B_x, and A_y, B_y, and A_z, B_z along rectangular Cartesian, x, y, and z axes, respectively, then

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, h_s )
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 +

)
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.

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Aerospace Science & Technology Dictionary

Aerospace Science
&
Technology Dictionary