A
A stars
   (NASA Thesaurus)
A class of stars in which spectral absorption lines for the Balmer series of hydrogen appear most prominently along with ionized metals. The A class serves as a central point from which other stellar spectra range. They are white stars ranging in temperature from 7000-9500 degrees Kelvin.
A-display
   (NASA SP-7, 1965)
In radar, a display in which targets appear as vertical deflections from a line representing a time base. Also called A-scan or A-scope .
Target distance is indicated by the horizontal position of the deflection from one end of the time base. The amplitude of the vertical deflection is a function of the signal intensity.
A-scan
   (NASA SP-7, 1965)
= A-display.
A-scope
   (NASA SP-7, 1965)
= A-display.
A-station
   (NASA SP-7, 1965)
In loran, the designation applied to the transmitting station of a pair, the signal of which always occurs less than half a repetition period after the next preceding signal and more than half a repetition period before the next succeeding signal of the other station of the pair, designated a B-station.
A-trace
   (NASA SP-7, 1965)
The first trace of an oscilloscope, as the upper trace of a loran indicator.
A/E ratio
   (NASA SP-7, 1965)
= absorptivity-emissivity ratio.
AAAS
   (Space Flight Glossary - JPL)
American Association for the Advancement of Science.
AACS
   (Space Flight Glossary - JPL)
Attitude and Articulation Control Subsystem onboard a spacecraft.
AAS
   (Space Flight Glossary - JPL)
American Astronomical Society.
aberration
   (NASA Thesaurus / NASA SP-7, 1965)
1. In astronomy, the apparent angular displacement of the position of a celestial body in the direction of motion of the observer, caused by the combination of the velocity of the observer and the velocity of light. See constant of aberration, planetary aberration. Compare parallax.
2. In optics, a specific deviation from perfect imagery, as, for example: spherical aberration, coma, astigmatism, curvature of field, and distortion.
aberration constant
   (NASA SP-7, 1965)
= constant of aberration
abiogenesis
   (NASA Thesaurus)
The development of living organisms from lifeless matter.
ablate
   (NASA SP-7, 1965)
To carry away; specifically, to carry away heat generated by aerodynamic heating, from a vital part, by arranging for its absorption in a nonvital part, which may melt or vaporize, then fall away taking the heat with it. See heat shield, ablation.
ablating materials
   (NASA Thesaurus / NASA SP-7, 1965)
See ablative materials.
ablation
   (NASA Thesaurus / NASA SP-7, 1965)
The removal of surface material from a body by vaporization, melting, chipping, or other erosive process; specifically, the intentional removal of material from a nose cone or spacecraft during high-speed movement through a planetary atmosphere to provide thermal protection to the underlying structure. See ablative materials.
ablation
   (Glossary of Hydrologic Terms - NOAA)
The process by which ice and snow waste away owing to melting and evaporation.
ablative materials
   (NASA Thesaurus / NASA SP-7, 1965)
A material, especially a coating material, designed to provide thermal protection to a body in a fluid stream through loss of mass.
Ablating materials are used on the surfaces of some reentry vehicles to absorb heat by removal of mass, thus blocking the transfer of heat to the rest of the vehicle and maintaining temperatures within design limits. Ablating materials absorb heat by increasing in temperature and changing in chemical or physical state. The heat is carried away from the surface by a loss of mass (liquid or vapor). The departing mass also blocks part of the convective heat transfer to the remaining material in the same manner as transpiration cooling.
ablative nose cones
   (NASA Thesaurus / NASA SP-7, 1965)
Nose cones designed to reduce heat transfer to the internal structure by the use of an ablative material.
ablatively
   (NASA SP-7, 1965)
By a process of ablation, as in ablatively cooled .
ablator
   (NASA SP-7, 1965)
A material designed to provide thermal protection through ablation.
abort
   (NASA SP-7, 1965)
1. To cut short or break off an action, operation, or procedure with an aircraft, space vehicle, or the like, especially because of equipment failure, as to abort a mission, the launching was aborted.
2. An aircraft, space vehicle, or the like that aborts.
3. An act or instance of aborting.
abrasion
   (NASA Thesaurus)
The surface loss of a material due to frictional forces.
abrasives
   (NASA Thesaurus)
Rocks, minerals, or other substances that, owing to their superior hardness, toughness, consistency, or other properties, are suitable for grinding, cutting, polishing, scouring, or similar use.
Abridged Nautical Almanac
   (NASA SP-7, 1965)
See Nautical Almanac.
absolute
   (NASA SP-7, 1965)
1. Pertaining to a measurement relative to a universal constant or natural datum, as absolute coordinate system, absolute altitude, absolute temperature.
2. Complete, as in absolute vacuum.
absolute altimeter
   (NASA SP-7, 1965)
An instrument intended to give acceptably accurate, direct indications of absolute altitude.
absolute altitude
   (NASA SP-7, 1965)
Altitude above the actual surface, either land or water, of a planet or natural satellite. Compare true altitude.
absolute coordinate system
   (NASA SP-7, 1965)
An inertial coordinate system which is fixed with respect to the stars.
In theory, no absolute coordinate system can be established because the reference stars are themselves in motion. In practice, such a system can be established to meet the demands of the problem concerned by the selection of appropriate reference stars.
absolute delay
   (NASA SP-7, 1965)
1. The time interval between the transmission of sequential signals. Also called delay .
2. Specifically, in loran, the time interval between transmission of a signal from the A-station and transmission of the next signal from the B-station.
absolute humidity
   (NASA SP-7, 1965)
The amount of water vapor actually present in unit quantity of a gas, generally expressed as mass of water vapor per unit volume of gas + water vapor, e.g., as grains per cubic foot.
absolute index of refraction
   (NASA SP-7, 1965)
= index of refraction (sense 1).
absolute instabilities
   (Plasma Physics and Fusion Energy Glossary)
A class of plasma instabilities growing exponentially with time at a point in space, in contrast to convective instabilities.
absolute instrument
   (NASA SP-7, 1965)
An instrument whose calibration can be determined by means of physical measurements on the instrument. Compare secondary instrument.
absolute magnitude
   (NASA SP-7, 1965)
(symbol M)
1. A measure of the brightness of a star equal to the magnitude the star would have at a distance of 10 parsecs from the observer.
M equals m plus five plus five log pi where m is apparent magnitude, and p is the parallax of the star (in seconds of arc). Absolute magnitudes may be visual, photographic, etc., according to the way in which the apparent magnitude was measured.
2. The stellar magnitude any meteor would have if placed in the observer's zenith at a height of 100 kilometers.
absolute magnitude
   (IMO Meteor Glossary)
The stellar magnitude any meteor would have if placed in the observer's zenith at a height of 100 km.
absolute magnitude (Ho)
   (Comet Glossary - JPL)
The brightness of a comet when it is at 1 AU from both the Earth and Sun. As this virtually never happens, this quantity is calculated from the comet's light curve. Unfortunately, this quantity is far from absolute. It can be different pre- and post-perihelion. It can also change from apparition to apparition (for periodic comets).
absolute manometer
   (NASA SP-7, 1965)
1. A gas manometer whose calibration, which is the same for all ideal gases, can be calculated from the measurable physical constants of the instrument.
2. A manometer that measures absolute pressure.
absolute motion
   (NASA SP-7, 1965)
Motion relative to a fixed point. See absolute coordinate system, note.
absolute pressure
   (NASA SP-7, 1965)
In engineering literature, a term used to indicate pressure above the absolute zero value of pressure that theoretically obtains in empty space or at the absolute zero of temperature as distinguished from gage pressure.
In high-vacuum technology, pressure is understood to correspond to absolute pressure, not gage pressure, and therefore the term absolute pressure is rarely used.
absolute refractive index
   (NASA SP-7, 1965)
= index of refraction (sense 1)
absolute system of units
   (NASA SP-7, 1965)
1. A system of units in which a small number of units are chosen as fundamental, and all other units are derived from them.
2. Specifically, a system of electrical units put into effect by international agreement on 1 January 1948.
Prior to 1 January 1948 the international system was in effect; the two systems can be converted by the following relationships:
1 mean international ohm = 1.00049 absolute ohm
1 mean international volt = 1.00034 absolute volt.

"Electric units, called "international," for current and resistance had been introduced by the International Electrical Congress held in Chicago in 1893, and the definitions of the international" ampere and the "international" ohm were confirmed by the International Conference of London in 1908.

Although it was already obvious on the occasion of the 8th CGPM (1933) that there was a unanimous desire to replace those "international" units by so-called "absolute" units, the official decision to abolish them was only taken by the 9th GPM (1948), which adopted for the unit of electric current, the ampere," which see.

The previous is an excerpt from WWW version of the National Institute of Standards and Technology: Physics Laboratory's International System of Units (SI).

absolute temperature
   (NASA SP-7, 1965)
Temperature value relative to absolute zero.
absolute temperature
   (From Stargazers to Starships Glossary - GSFC)
Temperature in degrees centigrade (also known in this case as "degrees Kelvin" K) measured from the absolute zero of -273.1 C, the temperature at which all atomic and molecular motions are expected to cease.
absolute temperature scale
   (NASA SP-7, 1965)
A temperature scale based upon the value zero as the lowest possible value. Thus, all obtainable temperatures are positive. The Kelvin and Rankine scales are absolute scales.
absolute vacuum
   (NASA SP-7, 1965)
A void completely empty of matter. Also called perfect vacuum.
An absolute vacuum is not obtainable.
absolute vorticity
   (NASA SP-7, 1965)
1. The vorticity of a fluid particle expressed with respect to an absolute coordinate system. 2. The vertical component of the absolute vorticity (as defined above).
absolute zero
   (NASA Thesaurus / NASA SP-7, 1965)
The theoretical temperature at which molecular motion vanishes and a body would have no heat energy; the zero point of the Kelvin and Rankine temperature scales.
Absolute zero may be interpreted as the temperature at which the volume of a perfect gas vanishes or, more generally, as the temperature of the cold source which would render a Carnot cycle 100 percent efficient. The value of absolute zero is now estimated to be - 273.15° Celsius, -459.67° Fahrenheit, 0° Kelvin, and 0° Rankine.
absorptance
   (NASA Thesaurus / NASA SP-7, 1965)
(absorbtance) (symbol A, a, or
)
The ratio of the radiant flux absorbed by a body to that incident upon it. Also called absorption factor. Compare absorptivity.
Total absorptance refers to absorptance measured over all wavelengths.
Spectral absorptance refers to absorptance measured at a specified wavelength.
absorption
   (Plasma Physics and Fusion Energy Glossary)
In plasma physics, the loss of (electromagnetic) energy to a medium. For instance, an electromagnetic wave which propagates through a plasma will set the electrons into motion. If the electrons make collisions with other particles, they will absorb net energy from the wave.
absorption
   (NASA Thesaurus / NASA SP-7, 1965)
1. The process by which radiant energy is absorbed and converted into other forms of energy. See attenuation.
Absorption takes place only after the radiant flux enters a medium and thus acts only on the entering flux not on the incident flux, some of which may be reflected at the surface of the medium. A substance which absorbs energy may also be a medium of refraction, diffraction, or scattering; these processes, however, involve no energy retention or transformation and are to be clearly differentiated from absorption.
2. In general, the taking up or assimilation of one substance by another. See sorption, adsorption.
3. In vacuum technology, gas entering into the interior of a solid.
absorption band
   (NASA SP-7, 1965)
A range of wavelengths (or frequencies) in the electromagnetic spectrum within which radiant energy is absorbed by a substance. See absorption spectrum.
When the absorbing substance is a polyatomic gas, an absorption band actually is composed of a group of discrete absorption lines which appear to overlap. Each line is associated with a particular mode of vibration or rotation induced in a gas molecule by the incident radiation.
The absorption bands of oxygen and ozone are often referred to in the literature of atmospheric physics.
The important bands for oxygen are: (a) the Hopfield bands, very strong, between about 670 and 1000 angstroms in the ultraviolet; (b) a diffuse system between 1019 and 1300 angstroms; (c) the Schumann-Runge continuum, very strong, between 1350 and 1760 angstroms; (d) the Schumann-Runge bands between 1760 and 1926 angstroms; (e) the Herzberg bands between 2400 and 2600 angstroms; (f) the atmospheric bands between 5380 and 7710 angstroms in the visible spectrum; and (g) a system in the infrared at about 1 micron.
The important bands for ozone are: (a) the Hartley bands between 2000 and 3000 angstroms in the ultraviolet, with a very intense maximum absorption at 2550 angstroms; (b) the Huggins bands, weak absorption between 3200 and 3600 angstroms; (c) the Chappius bands, a weak diffuse system between 4500 and 6500 angstroms in the visible spectrum; and (d) the infrared bands centered at 4.7, 9.6 and 14.1 microns, the latter being the most intense.
absorption coefficient
   (NASA SP-7, 1965)
(symbol alpha lower case)
1. A measure of the amount of normally incident radiant energy absorbed through a unit distance or by a unit mass of absorbing medium. Compare transmission coefficient.
The absorption coefficient is frequently identified as follows:
 

has an ALT text:   I(<sub>Lx )= I(<sub>L0) e (<sup>-k (<sup>L) x)
 

where ILx is the flux density of radiation of wavelength L, initially of flux density IL0, after traversing a distance x in some absorbing medium. (Substitute L for lambda.)

2. In acoustics, the ratio of the sound energy absorbed by a surface of a medium (or material) exposed to a sound field or sound radiation to the sound energy incident on the surface. The stated values of this ratio are to hold for an infinite area of the surface. The conditions under which measurements of absorption coefficients are made are to be stated explicitly.
Three types of absorption coefficients associated with three methods of measurement are: chamber absorption coefficient, obtained in a certain reverberation chamber; free-wave absorption coefficient, obtained when a plane, progressive, sound wave is incident on the surface of the medium; sabine absorption coefficient, obtained when the sound is incident from all directions on the sample.
absorption coefficient:
   (Plasma Physics and Fusion Energy Glossary)
Measures the degree of wave absorption (see Absorption above); defined as the fraction of wave energy lost as the wave travels a unit distance.
absorption cooling
   (NASA Thesaurus)
Refrigeration in which cooling is effected by the expansion of liquid ammonia into gas and the absorption of the gas by water. The ammonia is reused after the water evaporates.
absorption cross sections
   (NASA Thesaurus / NASA SP-7, 1965)
In radar, the ratio of the amount of power removed from a beam by absorption of radio energy by a target to the power in the beam incident upon the target. Compare scattering cross sections. See cross sections. Used for capture cross sections.
absorption factor
   (NASA SP-7, 1965)
= absorptance.
absorption line
   (NASA SP-7, 1965)
A minute range of wavelength (or frequency) in the electromagnetic spectrum within which radiant energy is absorbed by the medium through which it is passing. Each line is associated with a particular mode of electronic excitation induced in the absorbing atoms by the incident radiation. See absorption spectrum, spectral line, telluric lines, Fraunhofer lines, absorption band.
absorption spectra
   (NASA Thesaurus)
The arrays of absorption lines and absorption bands which result from the passage of radiant energy from a continuous source through a selectively absorbing medium cooler than the source. Used for absorption bands and spectral absorption.
absorption spectrum
   (NASA SP-7, 1965)
The array of absorption lines and absorption bands which results from the passage of radiant energy from a continuous source through a selectively absorbing medium cooler than the source. See electromagnetic spectrum.
The absorption spectrum is a characteristic of the absorbing medium, just as an emission spectrum is a characteristic of a radiator.
An absorption spectrum formed by a monatomic gas exhibits discrete dark lines, whereas that formed by a polyatomic gas exhibits ordered arrays (bands) of dark lines, which appear to overlap. This type of absorption is ften referred to as line absorption. The spectrum formed by a selectively absorbing liquid or solid is typically continuous in nature (continuous absorption).
absorption-emission pyrometer
   (NASA SP-7, 1965)
A thermometer for determining gas temperature from measurement of the radiation emitted by a calibrated reference source before and after this radiation has passed through and been partially absorbed by the gas. Both measurements are made over the same wavelength interval.
absorptive index
   (NASA SP-7, 1965)
The imaginary part of the complex index of refraction of a medium. It represents the energy loss by absorption and has a nonzero value for all media which are not dielectrics. Also called index of absorption . Compare absorption coefficient.
absorptive power
   (NASA SP-7, 1965)
The total flux of radiant energy absorbed in a unit area of absorbing substance; expressed, for example, in ergs per square centimeter per second or in watts per square centimeter.
absorptivity
   (NASA Thesaurus / NASA SP-7, 1965)
(symbol A sub infinite)
The capacity of a material to absorb incident radiant energy, measured as the absorptance of a specimen of the material thick enough to be completely opaque, and having an optically smooth surface.
absorptivity-emissivity ratio
   (NASA SP-7, 1965)
In space applications, the ratio of absorptivity for solar radiation of a material to its infrared emissivity. Also called A/E ratio.
abundance
   (NASA Thesaurus)
The mean concentration of an element in a geochemical reservoir, e.g., the abundance of Ni in meteorites or the crustal abundance of oxygen. Also used for the for relative average content, e.g., the order of abundance of elements in the Earth's crust is O, Si, AL, Fe, Ca, etc. Used for element abundance.
AC
   (Space Flight Glossary - JPL)
alternating current.
AC generators
   (NASA Thesaurus)
Generators for the production of alternating-current power. Used for alternating current generators and alternators (generators).
accelerated life tests
   (NASA Thesaurus)
Methods designed to approximate, in a short time, the deteriorating effects under normal long-term service conditions.
acceleration (physics)
   (NASA Thesaurus / NASA SP-7, 1965)
1. The rate of change of velocity.
2. The act or process of accelerating, or the state of being accelerated. Negative acceleration is called deceleration . Used for boost and G force.
acceleration of gravity
   (NASA SP-7, 1965)
(symbol g)
By the International Gravity Formula, g = 978.0495 [1 + 0.0052892 sin2(p) - 0.0000073 sin2 (2p)] centimeters per second squared at sea level at latitude p. See gravity.
The standard value of gravity, or normal gravity, g, is defined as go=980.665 centimeters per second squared, or 32.1741 feet per second squared. This value corresponds closely to the International Gravity Formula value of g at 45° latitude at sea level.
accelerator
   (NASA SP-7, 1965)
Short for particle accelerator .
accelerators
   (NASA Thesaurus)
Machines that ionize gases and electrically accelerate the ions onto targets.
accelerometers
   (NASA Thesaurus / NASA SP-7, 1965)
Transducers that measure acceleration or gravitational forces capable of imparting acceleration.
An accelerometer usually uses a concentrated mass (seismic mass) which resists movement because of its inertia. The displacement of the seismic mass relative to its supporting frame or container is used as a measure of acceleration.
acceptor
   (NASA SP-7, 1965)
In transistors, the P-type semiconductor, the electrode containing trivalent impurities (boron, gallium, or indium) to increase the number of holes which can accept electrons. Contrast with donor.
access control
   (NASA Thesaurus)
Hardware or software features, operating procedures, or management procedures designed to permit authorized access to a computer system.
accidental error
   (NASA SP-7, 1965)
In experimental observations, an error which does not always recur when an observation is repeated under the same conditions. Contrast systematic errors.
acclimatization
   (NASA Thesaurus / NASA SP-7, 1965)
The adjustments of a human body or other organism to a new environment; the bodily changes which tend to increase efficiency and reduce energy loss. Compare adaptation, accustomization.
accommodation coefficient
   (NASA Thesaurus / NASA SP-7, 1965)
(symbol alpha lower case)
The ratio of the average energy actually transferred between a surface and impinging gas molecules which are scattered by the surface to the average energy which would theoretically by transferred if the impinging molecules reached complete thermal equilibrium with the surface before leaving the surface or a = (Er-E i)/Es-Ei) where a is the accommodation coefficient, Er is the energy carried away from unit surface area per second by the scattered or re-evaporated molecules, Ei is the energy per unit surface area per second carried toward the surface by the impinging molecules, and Es is the energy per unit surface area per second which would be carried away by the molecules if the molecules reached complete thermal equilibrium with the surface before leaving.
accounting
   (NASA Thesaurus)
The practice and system of recording and summarizing business and financial transactions, and reporting as well as verifying and analyzing their results.
accretion
   (High Energy Astrophysics Dictionary- GSFC)
Accumulation of dust and gas into larger bodies such as stars, planets and moons.
accretion disks
   (NASA Thesaurus)
Rotating disks of matter surrounding an astronomical object, such as a star, galactic nucleus, black hole, etc., which is accumulated gravitationally by the object.
accretion disks
   (Spacetime Wrinkles Glossary)
In a binary system containing a star and a compact object (white dwarf, neutron star, or black hole) gas may flow from the star to the compact object. According to the theoretical model, the gas will spiral in and fall to the surface of the compact object creating a flow of matter in the shape of a disk. It is generally believed that this model explains many features of X-ray pulsars
accumulator
   (NASA Thesaurus / NASA SP-7, 1965)
1. A device or apparatus that accumulates or stores up, as: (a) a contrivance in a hydraulic system that stores fluid under pressure; (b) a device sometimes incorporated in the fuel system of a gas-turbine engine to store up and release fuel under pressure as an aid in starting; (c) an electrical storage battery (British usage).
2. In computer technology, a device which stores a number and upon receipt of another number adds it to the number already stored and stores the sum. See counter.
accuracy
   (NASA Thesaurus)
The degree of agreement of the measurements with the true value of the magnitude of the quantity measured. Used for error band and fidelity.
accustomization
   (NASA SP-7, 1965)
The process of learning the techniques of living with a minimum of discomfort in an extreme or new environment. Compare acclimatization, adaptation.
ACE
   (SOHO Glossary - GSFC)
Advanced Composition Explorer. A spacecraft studying the heliosphere and cosmic rays.
ACEE program
   (NASA Thesaurus)
A NASA program started in 1975 to reduce fuel consumption for transport aircraft through the study of structural and aerodynamic energy efficiency as well as engine energy efficiency consisting of engine component improvement, new energy efficient engines, and advanced turbopropellers. The acronym stands for aircraft energy efficiency. Used for Aircraft Energy Efficiency program and energy efficiency transport program.
acetylation
   (NASA Thesaurus)
Substitution of an acetyl radical for an active hydrogen. Specifically, formation of cellulose acetate from cellulose. Used for acetation.
acid rain
   (NASA Thesaurus)
Low pH rainfall resulting from atmospheric reactions of aerosols containing chlorides and sulfates (or other negative ions).
acidosis
   (NASA Thesaurus)
Reduction of alkali reserves due to an excess of acid metabolites.
aclinic line
   (NASA SP-7, 1965)
The line through those points on the earth's surface at which magnetic dip is zero. The aclinic line is a particular case of an isoclinic line. Also call dip equator, magnetic equator. Compare agonic line, geomagnetic equator.
acoustic delay lines
   (NASA Thesaurus / NASA SP-7, 1965)
Devices used in a communications link or a computer memory in which the signal is delayed by the propagation of a sound wave. Also called sonic delay lines .
acoustic description
   (NASA SP-7, 1965)
The change of speed of sound with frequency.
acoustic emission
   (NASA Thesaurus)
The stress and pressure waves generated during dynamic processes in materials and used in assessing structural integrity in machined parts.
acoustic excitation
   (NASA Thesaurus / NASA SP-7, 1965)
The process of inducing vibration in a structure by exposure to sound waves.
acoustic generator
   (NASA SP-7, 1965)
A transducer which converts electric, mechanical, or other forms of energy into sound.
acoustic levitation
   (NASA Thesaurus)
Method by which molten materials in space are suspended during processing experiments in the low gravity environment. Also, the use of very intense sound waves to keep a body suspended, thereby eliminating any container contact.
acoustic Mach meter
   (NASA SP-7, 1965)
A device which obtains data on sound propagation for the calculation of Mach number.
Some acoustics Mach meters measure transit time or velocity of a sound pulse; others measure an angle, as the angle of the Mach cone.
acoustic measurement
   (NASA Thesaurus)
Measurement of properties, quantities, or conditions of acoustical, i.e., mechanical waves. Used for sound measurement.
acoustic microscopes
   (NASA Thesaurus)
Instruments which use acoustic radiation at microwave frequencies to allow visualization of microscopic detail exhibited in elastic properties of objects. Used for scanning laser acoustic microscope (SLAM).
acoustic radiation pressure
   (NASA SP-7, 1965)
A unidirectional, steady-state pressure exerted upon a surface exposed to a sound wave.
acoustic refraction
   (NASA SP-7, 1965)
The process by which the direction of sound propagation is changed due to spatial variation in the speed of sound in the medium.
acoustic retrofitting
   (NASA Thesaurus)
Modification, especially of aircraft, to effect noise reduction; specifically, the introduction of absorber materials and jet noise silencers.
acoustic streaming
   (NASA Thesaurus / NASA SP-7, 1965)
Unidirectional flow currents in a fluid that are due to the presence of sound waves.
acoustic velocity
   (NASA Thesaurus / NASA SP-7, 1965)
(symbol alpha lower case)
=speed of sound
acoustic vibration
   (NASA SP-7, 1965)
With respect to operational environments, vibrations transmitted through a gas. These vibrations may be subsonic, sonic, and ultrasonic.
acoustic wave
   (NASA SP-7, 1965)
= sound wave.
acoustic, acoustical
   (NASA SP-7, 1965)
Containing, producing, arising from, actuated by, related to, or associated with sound.
Acoustic is used to modify terms that designate an object, or physical characteristics, associated with sound waves; acoustical is used when the term being qualified does not designate explicitly something that has such properties, dimensions, or physical characteristics.
The following terms are examples of those modified by acoustic; impedance, intertance, load (radiation field), output (sound power), energy, wave, medium, signal, conduit, absorptivity, transducer.
The following examples do not have the requisite physical characteristics and therefore take acoustical; society, method, engineer, school, glossary, symbol, problem, measurement, point of view, device.
As illustrated, the generic term is usually modified by acoustical, whereas the specific technical term calls for acoustic.
acoustics
   (NASA Thesaurus / NASA SP-7, 1965)
1. The study of sound, including its production, transmission, and effects.
2. Those qualities of an enclosure that together determine its character with respect to distinct hearing.
acquired immunodeficiency syndrome
   (NASA Thesaurus)
A condition caused by the human immunodeficiency virus (HIV) attacking the human body's T-cells, thereby rendering an infected individual defenseless against diseases.
acquisition
   (NASA SP-7, 1965)
1. The process of locating the orbit of a satellite or trajectory of a space probe so that tracking or telemetry data can be gathered.
2. The process of pointing an antenna or telescope so that it is properly oriented to allow gathering of tracking or telemetry data from a satellite or space probe.
acquisition and tracking radar
   (NASA SP-7, 1965)
A radar set that locks onto a strong signal and track the object reflecting the signal.
actinic
   (NASA SP-7, 1965)
Pertaining to electromagnetic radiation capable of initiating photochemical reactions, as in photography or the fading of pigments.
Because of the particularly strong action of ultra violet radiation on photochemical processes, the term has come to be almost synonymous with ultraviolet, as in actinic rays.
actinic balance
   (NASA SP-7, 1965)
=bolometer.
actinide series
   (NASA Thesaurus)
The series of elements beginning with actium, element No. 89, and continuing through lawrencium, element No. 103.
actinogram
   (NASA SP-7, 1965)
The record of a recording actinometer.
actinograph
   (NASA SP-7, 1965)
A recording actinometer.
actinometer
   (NASA Thesaurus / NASA SP-7, 1965)
The general name for any instrument used to measure the intensity of radiant energy, particularly that of the sun. See actinometry. See also bolometer, dosimeter, photometer, radiometer.
Actinometers may be classified, according to the quantities which they measure, in the following manner: (a) pyrheliometer, which measures the intensity of direct solar radiation; (b) pyranometer, which measure global radiation (the combined intensity of direct solar radiation and diffuse sky radiation); and (c) pyrgeometer, which measures the effective terrestrial radiation.
actinometry
   (NASA SP-7, 1965)
The science of measurement of radiant energy, particularly that of the sun, in its thermal, chemical, and luminous aspects. Compare photometry. See actinometer.
activated sludge
   (NASA Thesaurus)
A semiliquid mass removed from the liquid flow of sewage and subjected to aeration and aerobic microbial action. The end product is dark to golden brown, partially decomposed, granular and flocculent, and has an earthy odor when fresh.
activation
   (Plasma Physics and Fusion Energy Glossary)
Activation occurs when a particle interacts with an atomic nucleus, shifting the nucleus into an unstable state, and causing it to become radioactive. In fusion research, where deuterium-tritium is a common fuel mixture, the neutron released when (D + T) combine to form (4He + n) can activate the reactor structure. In this case the 4He is inert, the neutron sticks to another nucleus, and the neutron + nucleus reaction creates an actvation product. Sometimes called "radioactivation."
activation analysis
   (NASA Thesaurus)
A method of chemical analysis, especially for small traces of materials, based on the detection of characteristic radiations following a nuclear bombardment.
activation analysis
   (Plasma Physics and Fusion Energy Glossary)
Method for identifying and measuring chemical elements in a sample of material. Sample is first made radioactive by bombardment with neutrons, charged particles, or gamma rays. Newly formed radioactive atoms in the sample then give off characteristic radiations (such as gamma rays) that tell what kinds of atoms are present, and how many.
activation product
   (Plasma Physics and Fusion Energy Glossary)
The unstable nucleus formed when activation occurs
active
   (NASA SP-7, 1965)
1. Transmitting a signal, as active satellite . Antonym of passive.
2. = radioactive, as active sample .
3. = fissionable, as active material .
4. Receiving energy from some source other than a signal, as active element .
active control
   (NASA Thesaurus)
The automatic activation of various control surface functions in aircraft.
active element
   (NASA SP-7, 1965)
In a computer, a circuit or device which receives energy from some source other than the signal input.
active galactic nuclei
   (High Energy Astrophysics Dictionary- GSFC)
Normal galaxies with a massive black hole accreting gas at its center, thus producing enormous amounts of energy at all wavelengths of the electromagnetic spectrum.
active homing
   (NASA SP-7, 1965)
The homing of an aerodynamic or space vehicle in which energy waves (as radar) are transmitted from the vehicle to the target and reflected back to the vehicle to direct the vehicle toward the target. Compare passive homing.
active homing guidance
   (NASA SP-7, 1965)
See homing guidance.
active leg
   (NASA SP-7, 1965)
An electrical element within a transducer which changes its electrical characteristics as a function of the application of a stimulus.
active region
   (SOHO Glossary - GSFC)
An area of the Sun where the magnetic fields are very strong. At ultraviolet and X-ray wavelengths they appear bright. In visible light they exhibit sunspots.
active satellite
   (NASA Thesaurus / NASA SP-7, 1965)
A satellite which transmits a signal, in contrast to passive satellite .
active tracking system
   (NASA SP-7, 1965)
A system which requires addition of a transponder, or transmitter on board the vehicle to repeat, transmit, or retransmit information to the tracking equipment, e.g. Dovap, Secor, Azusa, Miran, Minitrack.
active transducer
   (NASA SP-7, 1965)
A transducer whose output is dependent upon sources of power, apart from that supplied by any of the actuating signals, which power is controlled by one or more of these signals.
actuating system
   (NASA SP-7, 1965)
A mechanical system that supplies and transmits energy for the operation of other mechanisms or systems.
actuators
   (NASA Thesaurus)
Mechanisms to activate process control equipment, e.g., valves. Used for cartridge actuated devices, hydraulic actuators, and triggers.
acuity
   (NASA Thesaurus)
The keeness of ability to detect and discriminate.
Ada (programming language)
   (NASA Thesaurus)
A programming language based on PASCAL, originally developed on behalf of the US Department of Defense for use in embedded computer systems. It is named Ada in honor of Augusta Ada Byron, countess of Lovelace, primarily due to the fact that she was the assistant and patron of Charles Babbage and is considered the world's first programmer.
adaptation
   (NASA Thesaurus / NASA SP-7, 1965)
The adjustment, alteration, or modification of an organism to fit it more perfectly for existence in its environment. Compare acclimatization, accustomization.
Adaptation is applied particularly to evolutionary change.
adaptation brightness
   (NASA SP-7, 1965)
= adaptation luminance.
adaptation illuminance
   (NASA SP-7, 1965)
= adaptation luminance.
adaptation level
   (NASA SP-7, 1965)
= adaptation luminance.
adaptation luminance
   (NASA SP-7, 1965)
The average luminance (or brightness) of those objects and surfaces in the immediate vicinity of an observer. Also called adaptation brightness, adaptation level, adaptation illuminance.
The adaptation luminance has a marked influence on an observer's estimate of the visual range because, along with the visual angle of the object under observation, it determines the observer's threshold contrast. High adaptation luminance tends to produce a high threshold contrast, thus reducing the estimated visual range. This effect of the adaptation luminance is to be distinguished from the influence of background luminance.
adapter
   (NASA Thesaurus / NASA SP-7, 1965)
1. Any device or contrivance used or designed primarily to fit or adjust one thing to another, as: (a) a buckle or clip on a parachute harness, used in adjusting the harness to the wearer; (b) a joint attaching an afterburner to a turbine casing on a jet engine; (c) a fitting for connecting pipes, valves, etc., that have different types of threads.
2. Any device, appliance or the like used to alter something so as to make it suitable for a use for which it was not originally designed.
adapter skirt
   (NASA SP-7, 1965)
A flange or extension of a space vehicle stage or section that provides a ready means for fitting some object to the stage or section.
adaptive control system
   (NASA SP-7, 1965)
A control system which continuously monitors the dynamic response of the controlled system and automatically adjusts critical system parameters to satisfy preassigned response criteria, thus producing the same response over a wide range of environmental conditions.
adaptive optics
   (NASA Thesaurus)
Real-time optical correction for atmospheric perturbations and other system error sources.
ADC (abbr)
   (NASA SP-7, 1965)
= analog to digital converter.
Adcock antenna
   (NASA SP-7, 1965)
A pair of vertical antennas separated by a distance of one-half wavelength or less, and connected in phase opposition to produce a radiation pattern having the shape of a figure eight.
adder
   (NASA SP-7, 1965)
In a computer, a device which can form the sum of two or more numbers or quantities.
additional apparent mass
   (NASA SP-7, 1965)
= apparent additional mass.
additive
   (NASA Thesaurus / NASA SP-7, 1965)
Any material or substance added to something else. Specifically, a substance added to a propellant to achieve some purpose, such as a more even rate of combustion, or a substance added to fuels or lubricants to improve them or give them some desired quality, such as tetraethyl lead added to a fuel as an antidetonation agent, or graphite, talc, or other substances added to certain oils and greases to improve lubrication qualities.
address
   (NASA SP-7, 1965)
1. Of a computer, a location where information is stored.
2. An expression, usually numerical, identifying an address (sense 1).
adducts
   (NASA Thesaurus)
Chemical compounds with weak bonds, e.g., occlusive or Van der Waal bonds.
ADF
   (NASA SP-7, 1965)
= automatic direction finder.
adiabat
   (NASA SP-7, 1965)
A line on a thermodynamic diagram representing a constant potential temperature. See adiabatic process.
adiabatic
   (NASA SP-7, 1965)
Without gain or loss of heat.
adiabatic
   (Plasma Physics and Fusion Energy Glossary)
Not involving an exchange of heat between the system said to be adiabatic and the rest of the universe.
adiabatic atmosphere
   (NASA SP-7, 1965)
A model atmosphere in which the pressure decreases with height according to: p = p0[1 - (-gz/cp,dT0)] Cp,dRd where p0 and T0 are the pressure and temperature (° K) at sea level or other datum; z is the geometric height; Rd is the gas constant for dry gas; cp,d is the specific heat for dry gas at constant pressure; and g is the acceleration of gravity. Also called dry-adiabatic atmosphere, convective atmosphere, homogeneous atmosphere . See homogeneous atmosphere, barotropy.
adiabatic compression
   (NASA SP-7, 1965)
See adiabatic process.
adiabatic compression
   (Plasma Physics and Fusion Energy Glossary)
Compression (of a gas, plasma, etc.) not accompanied by gain or loss of heat from outside the system. For a plasma in a magnetic field, a compression slow enough that the magnetic moment (and other adiabatic invariants - see entry) of the plasma particles may be taken as constant.
adiabatic demagnetization cooling
   (NASA Thesaurus)
Use of paramagnetic salts cooled to the boiling point of helium in a strong magnetic field, then thermally isolated and removed from the field to demagnetize the salts and attain temperatures of 10(-3) K.
adiabatic efficiency
   (NASA SP-7, 1965)
The efficiency with which work is done with respect to heat gains or losses. See adiabatic process.
adiabatic equivalent temperature
   (NASA SP-7, 1965)
See equivalent temperature, sense 2.
adiabatic invariant
   (Plasma Physics and Fusion Energy Glossary)
Characteristic parameters which do not change as a physical system slowly evolves; the most commonly used one in plasma physics is the magnetic moment of a charged particle spiraling around a magnetic field line
adiabatic invariant
   (Earth's Magnetosphere Glossary - GSFC)
Adiabatic invariants are quantities associated with approximately periodic motions. They almost do not change, and thus also help in calculating the motion, to a very good degree of accuracy. They are often important in calculating the way ions and electrons move in a magnetic field. (Plasma Physics and Fusion Energy Glossary) Characteristic parameters which do not change as a physical system slowly evolves; the most commonly used one in plasma physics is the magnetic moment of a charged particle spiraling around a magnetic field line.
adiabatic process
   (NASA SP-7, 1965)
A thermodynamic change of state of a system in which there is no transfer of heat or mass across the boundaries of the system. In an adiabatic process, compression always results in warming, expansion in cooling. See diabatic process.
adiabatic recovery temperature
   (NASA SP-7, 1965)
1. The temperature reached by a moving fluid when brought to rest through an adiabatic process. Also called recovery temperature, stagnation temperature .
2. = adiabatic wall temperature.
3. The final and initial temperature in an adiabatic, Carnot cycle.
adiabatic wall temperature
   (NASA SP-7, 1965)
The temperature assumed by a wall in a moving fluid stream when there is no heat transfer between the wall and the stream.
ADP (abbr)
   (NASA SP-7, 1965)
= automatic data processing.
Adrastea
   (NASA Thesaurus)
A natural satellite of Jupiter orbiting at a mean distance of 129,980 kilometers.
adsorbate
   (NASA SP-7, 1965)
In the process of adsorption, the adsorbed substance.
adsorbent
   (NASA Thesaurus / NASA SP-7, 1965)
A material which takes up gas by adsorption.
adsorption
   (NASA Thesaurus / NASA SP-7, 1965)
The adhesion of a thin film of liquid or gas to the surface of a solid substance. The solid does not combine chemically with the adsorbed substance. See sorption, absorption, chemisorption.
Advanced Composition Explorer
   (NASA Thesaurus)
Explorer spacecraft (launched August 25, 1997) carrying six high-resolution sensors and three monitoring instruments for sampling low-energy particles of solar origin and high-energy galactic particles. From a vantage point approximately 1/100 of the distance from the Earth to the Sun, the Advanced Composition Explorer (ACE) can perform measurements over a wide range of energy and nuclear mass, under all solar wind flow conditions and during both large and small particle events including solar flares. When reporting space weather ACE can provide an advance warning of geomagnetic storms.
Advanced Concepts Torus I
   (Plasma Physics and Fusion Energy Glossary)
(ACT-I) A steady-state toroidal device built primarily for studies of RF heating and RF current drive. Operated at PPPL but shut down several years ago.
Advanced Microwave Sounding Unit
   (NASA Thesaurus)
A line-scan instrument on the Advanced TIROS-N (ATN) NOAA K-N series of operational meteorological satellites. The AMSU consists of two functionally independent units, AMSU-A and AMSU-B. The AMSU-A is designed to measure scene radiance in 15 channels, ranging from 23.8 to 89 GHz, to derive atmospheric temperature profiles from the Earth surface to about 3 millibar pressure height. The AMSU-B is designed to measure scene radiance in five channels, ranging from 89 GHz to 183 GHz for the computation of atmospheric water vapor profiles.
Advanced Range Instrumentation Aircraft
   (NASA Thesaurus)
An EC-135 aircraft configured for reception recording and real-time relay of telemetry data.
Advanced Technology Laboratory
   (NASA Thesaurus)
An all-pallet payload utilizing the Space Shuttle and the European Spacelab and designed to accommodate 8 to 15 experiments per mission.
Advanced Toroidal Facility: (ATF)
   (Plasma Physics and Fusion Energy Glossary)
(ATF) A large stellarator device developed at Oak Ridge National Lab (ORNL),
Advanced Very High Resolution Radiometer
   (Global Land Information System Glossary - USGS)
The AVHRR is a broad-band, 4 or 5 channel scanner (depending on the model), sensing in the visible, near-infrared, and thermal infrared portions of the electromagnetic spectrum. This sensor is carried on NOAA's Polar Orbiting Environmental Satellites (POES), beginning with TIROS-N in 1978.
Advanced Very High Resolution Radiometer
   (NASA Thesaurus)
A five channel scanning instrument that quantitatively measures electromagnetic radiation.
advection
   (NASA Thesaurus / NASA SP-7, 1965)
The process of transport of an atmospheric property solely by the mass motion of the atmosphere; also, the rate of change of the value of the advected property at a given point.
Regarding the general distinction (in meteorology) between advection and convection, the former describes the predominantly horizontal, large-scale motions of the atmosphere whereas convection describes the predominantly vertical, locally induced motions.
advective
   (NASA SP-7, 1965)
Pertaining to advection .
aeon
   (NASA SP-7, 1965)
109 years. This term was suggested by Harold Urey in 1957.
aeration zone
   (Glossary of Hydrologic Terms - NOAA)
A portion of the lithosphere in which the functional interstices of permeable rock or earth are not filled with water under hydrostatic pressure. The interstices either are not filled with water or are filled with water that is no held by capillarity.
aerial
   (NASA SP-7, 1965)
1. = antenna.
2. Of or pertaining to the air, atmosphere, or aviation.
aerial archeology
   (AS&T Dictionary)
The location and study of archeological sites through observation or remote sensing from aircraft or airborne platforms.
aero-otitis media
   (NASA SP-7, 1965)
An inflammatory reaction of the middle ear resulting from a difference in pressure between the gas in the middle ear and the surrounding atmosphere. Also called otitic barotrauma . c
aeroassist
   (NASA Thesaurus)
Changing orbit size by utilizing aerobraking, aerocapture, or aeromaneuvering.
aeroastromedicine
   (NASA SP-7, 1965)
= aerospace medicine.
aeroballistics
   (NASA SP-7, 1965)
The study of the interaction of projectiles or high speed vehicles with the atmosphere. See ballistics.
The problem of the effect of reentry on the trajectory of a vehicle is a problem in aeroballistics.
aerobiology
   (NASA Thesaurus / NASA SP-7, 1965)
The study of the distribution of living organisms freely suspended in the atmosphere.
aerobraking
   (NASA Thesaurus)
Changing orbit size by using the upper atmosphere to create drag.
aerocapture
   (NASA Thesaurus)
Making use of the atmosphere of a planet or planetary satellite by capturing the object and reducing the orbit size so that it remains in orbit or lands on the body.
aerodontalgia
   (NASA SP-7, 1965)
A toothache brought on by a change in ambient pressure.
aeroduct
   (NASA SP-7, 1965)
A ramjet type of engine designed to scoop up ions and electrons freely available in the outer reaches of the atmosphere or in the atmospheres of other spatial bodies, and by a metachemical process within the duct of this engine, expel particles derived from the ions and electrons as a propulsive jetstream.
aerodynamic
   (NASA SP-7, 1965)
Of or pertaining to aerodynamics.
aerodynamic coefficient
   (NASA Thesaurus / NASA SP-7, 1965)
Any nondimensional coefficient relating to aerodynamic forces or moments, such as a coefficient of drag, a coefficient of lift, etc.
aerodynamic force
   (NASA Thesaurus / NASA SP-7, 1965)
The force exerted by a moving gaseous fluid upon a body completely immersed in it.
The aerodynamic force is proportional to the expression
p u 2 L 2 R n

where p is the fluid density; u is the velocity of the undisturbed stream relative to the body; L is a characteristic linear dimension of the body; and Rn is the Reynolds number raised to the power of n, a constant usually determined experimentally. This form for the aerodynamic force is sometimes called
Rayleigh formula. The component of the aerodynamic force parallel to the direction of flow is called the drag.
aerodynamic heating
   (NASA Thesaurus / NASA SP-7, 1965)
The heating of a body produced by passage of air or other gases over the body; caused by friction and by compression processes and significant chiefly at high speeds. See radiative heating.
aerodynamic trail
   (NASA SP-7, 1965)
A condensation trail formed by adiabatic cooling to saturation (or slightly supersaturation) of air passing over the surfaces of high-speed aircraft.
Aerodynamic trails form off the tips of wings and propellers and other points of maximum pressure decrease. They are relatively rare and of short duration compared to exhaust trails.
aerodynamic vehicle
   (NASA SP-7, 1965)
A device, such as an airplane, glider, etc., capable of flight only within a sensible atmosphere and relying on aerodynamic forces to maintain flight.
The term is used when the context calls for discrimination from space vehicle.
aerodynamics
   (NASA Thesaurus / NASA SP-7, 1965)
1. The science that deals with the motion of air and other gaseous fluids, and of the forces acting on bodies when the bodies move through such fluids, or when such fluids move against or around the bodies, as, his research in aerodynamics .
2. (a) The actions and forces resulting from the movement or flow of gaseous fluids against or around bodies, as, the aerodynamics of a wing in supersonic flight . (b) The properties of a body or bodies with respect to these actions or forces, as, the aerodynamics of a turret or of a configuration .
3. The application of the principles of gaseous fluid flows and of their actions against and around bodies to the design and construction of bodies intended to move through such fluids, as a design used in aerodynamics.
aeroelastic research wings
   (NASA Thesaurus)
Wings that are designed with less than normal stiffness to test devices that suppress flutter.
aeroelasticity
   (NASA Thesaurus / NASA SP-7, 1965)
The study of the response of structurally elastic bodies to aerodynamic loads.
aeroembolism
   (NASA Thesaurus / NASA SP-7, 1965)
1. The formation or liberation of gases in the blood vessels of the body, as brought on by a too-rapid change from a high, or relatively high, atmospheric pressure to a lower one.
2. The disease or condition caused by the formation of gas bubbles (mostly nitrogen) in the body fluids. The disease is characterized principally by neuralgic pains, cramps, and swelling, and sometimes results in death. Also call decompression sickness .
aeroemphysema
   (NASA SP-7, 1965)
A swelling condition caused by the formation of gas in the tissues of the body.
aerolite
   (NASA SP-7, 1965)
A meteorite composed principally of stony material.
aerology
   (NASA Thesaurus / NASA SP-7, 1965)
1. As officially used in the U.S. Navy until early 1957, same as meteorology; this usage was more administrative than scientific.
2. As a subdivision of meteorology, the study of the free atmosphere through its vertical extend, as distinguished from studies confined to the layer of the atmosphere adjacent to the earth's surface.
aeromagnetic
   (Global Land Information System Glossary - USGS)
Aeromagnetic is descriptive of data pertaining to the Earth's magnetic field which has been collected from an airborne sensor.
aeromaneuvering
   (NASA Thesaurus)
Changing orbit size or plane or both by entering the upper atmosphere to create drag or lift or both.
Aeromaneuvering Orbit to Orbit Shuttle
   (NASA Thesaurus)
Proposed reusable upper stage for the Space Shuttle superseded by the orbit transfer vehicle. Used for AMOOS.
aeronomy
   (NASA Thesaurus / NASA SP-7, 1965)
The study of the upper regions of the atmosphere where ionization, dissociation, and chemical reactions take place.
aeropause
   (NASA SP-7, 1965)
A region of indeterminate limits in the upper atmosphere, considered as a boundary or transition region between the denser portion of the atmosphere and space.
From a functional point of view, it is considered to be that region in which the atmosphere is so tenuous as to have a negligible, or almost negligible, effect on men and aircraft, and in which the physiological requirements of man become increasingly important in the design of aircraft and auxiliary equipment.
aerophare
   (NASA SP-7, 1965)
=radio beacon .
aeropulse engine
   (NASA SP-7, 1965)
= pulsejet engine.
Aerosat satellites
   (AS&T Dictionary)
Satellites developed for aeronautical applications as part of a joint U.S., European Space Agency and Canadian program during the late-1960s and early-1970s. The Aerosat system uses two geostationary satellites over the Atlantic to provide voice and data links to transatlantic aircraft and to determine and monitor aircraft positions.
aeroshells
   (NASA Thesaurus)
Aerodynamic structural shells that attach to, or comprise a portion of, the exterior of an aerospace vehicle or space probe; especially such structures that support atmospheric entry, aerobraking, aeroassist, or hypersonic flight.
aerosinusitis
   (NASA SP-7, 1965)
An inflammatory reaction of one or more of the accessory nasal sinuses resulting from a difference in pressure between the gas in the sinus and the surrounding atmosphere. Also called sinus barotrauma .
aerosols
   (NASA Thesaurus)
Dispersions of solid or liquid particles in gaseous media.
aerosonator
   (NASA SP-7, 1965)
= resojet engine.
aerospace
   (NASA SP-7, 1965)
(From aeronautics and space).
1. Of or pertaining to both the earth's atmosphere and space, as in aerospace industries.
2. Earth's envelope of air and space above it; the two considered as a single realm for activity in the flight of air vehicles and in the launching, guidance, and control of ballistic missiles, earth satellites, dirigible space vehicles, and the like.
Aerospace in sense 2 is used primarily by the U.S. Air Force. The term aerospace first appeared in print in the Interim Glossary; Aero-Space Terms (edited by Woodford Agee Heflin) published in February 1958 at the Air University, Maxwell Air Force Base, Alabama.
aerospace medicine
   (NASA Thesaurus / NASA SP-7, 1965)
That branch of medicine dealing with the effects of flight through the atmosphere or in space upon the human body and with the prevention or cure of physiological or psychological malfunctions arising from these effects.
aerospace safety
   (NASA Thesaurus)
The engineering assessment and analysis of systems, subsystems, and functions of spacecraft, missiles, advanced aircraft and ground support in order to identify hazards associated with such systems and to design procedures that eliminate those hazards or determine tolerable safety levels.
aerospace technology transfer
   (NASA Thesaurus)
Technology transfer germane to aircraft and space vehicles, their propulsion, guidance, etc.
aerospace vehicle
   (NASA Thesaurus / NASA SP-7, 1965)
A vehicle capable of flight within and outside the sensible atmosphere.
aerospike engines
   (NASA Thesaurus)
Rocket engines incorporating a radial in-flow (aerospike) nozzle for altitude compensation. Since the nozzle is open to the ambient atmosphere, the plume compensates for decreasing atmospheric pressure as the vehicle ascends.
aerothermodynamic border
   (NASA SP-7, 1965)
An altitude at about 100 miles, above which the atmosphere is so rarefied that the skin of an object moving through it at high speeds generates no significant heat.
aerothermodynamic duct
   (NASA SP-7, 1965)
The full term for athodyd .
aerothermodynamics
   (NASA Thesaurus / NASA SP-7, 1965)
The study of aerodynamic phenomena at sufficiently high gas velocities that thermodynamic properties of the gas are important.
aerothermoelasticity
   (NASA Thesaurus / NASA SP-7, 1965)
The study of the response of elastic structures to the combined effect of aerodynamic heating and loading.
aerozine
   (NASA Thesaurus)
A rocket fuel consisting of a mixture of hydrazine and unsymmetrical dimethylhydrazine (UDMH).
AFC (abbr)
   (NASA SP-7, 1965)
= automatic frequency control.
afterbody
   (NASA Thesaurus / NASA SP-7, 1965)
1. A companion body that trails a satellite.
2. A section or piece of a rocket or spacecraft that enters the atmosphere unprotected behind the nose cone or other body that is protected for entry.
3. The afterpart of a vehicle.
afterburner
   (NASA SP-7, 1965)
A device for augmenting the thrust of a jet engine by burning additional fuel in the uncombined oxygen in the gases from the turbine.
afterburning
   (NASA Thesaurus / NASA SP-7, 1965)
1. Irregular burning of fuel left in the firing chamber or a rocket after fuel cutoff.
2. The function of an afterburner, a device for augmenting the thrust of a jet engine by burning additional fuel in the uncombined oxygen in the gases from the turbine.
aftercooling
   (NASA SP-7, 1965)
1. The cooling of a gas after compression.
2. The necessary cooling of a reactor core after its shutdown by pumping a liquid or gas through it to carry off the excess heat generated by continuing radioactive decay of fission products within the core.
aftercooling:
   (Plasma Physics and Fusion Energy Glossary)
Cooling of a reactor after it has been shut down.
afterglow
   (NASA Thesaurus / NASA SP-7, 1965)
1. A broad, high arch of radiance or glow seen occasionally in the western sky above the highest clouds in deepening twilight, caused by the scattering effect of very fine particles of dust suspended in the upper atmosphere.
2. The transient decay of a plasma after the power has been turned off.
The decay time involved is a direct consequence of the charged particle loss mechanisms, such as diffusion and recombination. The magnitude of these quantities is determined by measuring the decay time under controlled conditions.
afterglow
   (Plasma Physics and Fusion Energy Glossary)
Recombination radiation emitted from a cooling plasma when the source of ionization (heating, etc) is removed.
afterheat
   (NASA SP-7, 1965)
The heat generated in a reactor core after shutdown by continuing radioactive decay of fission products.
AGE (abbr)
   (NASA SP-7, 1965)
= aerospace ground equipment. See GSE.
age of the moon
   (NASA SP-7, 1965)
The elapsed time, usually expressed in days, since the last new moon. See phases of the moon.
agents of change
   (Galileo Project Glossary - JPL)
The constructive and destructive processes that reshape a planetary surface.
agglomerate
   (Glossary of Hydrologic Terms - NOAA)
An ice cover of floe formed by the freezing together of various forms of ice.
aging
   (NASA SP-7, 1965)
In a metal or alloy, a change in properties that generally occurs slowly at room temperature and more rapidly at higher temperatures.
Agiwarn
   (NASA SP-7, 1965)
Code name for the Western Hemisphere Regional Center for the IGY World Warning Agency.
agonic line
   (NASA SP-7, 1965)
A line joining points at which the magnetic variation is zero. The agonic line is a particular case of an isogonic line.
agravic
   (NASA SP-7, 1965)
Or pertaining to a condition of no gravitation. See weightlessness.
agravic illusion
   (NASA SP-7, 1965)
An apparent movement of a target in the visual field due to otolith response in zerogravity. Also called oculoagravic illusion .
agricultural aircraft
   (NASA Thesaurus)
Light aircraft specially equipped for agricultural applications such as crop dusting.
AgRISTARS project
   (NASA Thesaurus)
A multiagency program utilizing Landsat remote sensing data to predict crop yields, land use, and detect pollution. Used for Crop Inventories by Remote Sensing.
agrophysical units
   (NASA Thesaurus)
Geographic areas defined for statistical purposes by AgRISTARS personnel whose boundaries are based on natural rather than political lines for the purpose of comparing similar agricultural regions.
AH-1G helicopter
   (NASA Thesaurus)
US Army designation for the Bell Model 209 Hueycobra attack helicopter powered by a single Avco Lycoming T53-L-13 turboshaft engine.
air
   (NASA Thesaurus / NASA SP-7, 1965)
1. The mixture of gases comprising the earth's atmosphere.
The percent by volume of those gases found in relatively constant amount in dry air near sea level in very nearly as follows:

.

ELEMENT

%

nitrogen (N2) 78.084
oxygen (O2) 20.9476
argon (A) 0.934
carbon dioxide (CO2) 0.0314 (variable)
neon (Ne) 0.001818
helium (He) 0.000524
methane (CH4) 0.0002 (variable)
krypton (Kr) 0.000114
hydrogen (H2) 0.00005
nitruous oxide (N2O) 0.00005
xenon (Xe) 0.0000087

air breakup
   (NASA SP-7, 1965)
The breakup of a test reentry body after reentry into the atmosphere.
Air breakup is sometimes provided for, as by the firing of a cartridge inside the reentry body, so as to retard the fall of certain pieces and increase the chances of their recovery. See blowoff.
air breathing boosters
   (NASA Thesaurus)
Boosters which are possible substitutes for rocket engines and which have inlets for oxygen sources for their engines rather than carrying their own oxygen as in a conventional rocket.
air breathing engines
   (AS&T Dictionary)
An aircraft or spacecraft propulsion system which sustains combustion of fuel with the intake of atmospheric oxygen and therefore cannot operate beyond the atmosphere.
air conditioning
   (NASA Thesaurus)
The simultaneous control of all, or at least three, of those factors affecting both the physical and chemical conditions of the atmosphere within any structure. These factors include temperature, humidity, motion, distribution, dust, bacteria, odor, and toxic gases.
air cushion landing systems
   (NASA Thesaurus)
Landing systems based on the ground effect principle whereby a stratum of air is utilized as the aircraft ground contacting medium (in place of landing gear).
air data systems
   (NASA Thesaurus)
Sets of aerodynamic and thermodynamic sensors, and a computer which provide flight characteristics such as airspeed, static pressure, air temperature and Mach number.
air launch
   (NASA SP-7, 1965)
To launch from an aircraft in the air, as to air launch a guided missile .
air law
   (NASA Thesaurus)
The body of domestic and/or international laws dealing with regulations and liabilities in civil or military aviation.
air light
   (NASA SP-7, 1965)
Light from sun and sky which is scattered into the eyes of an observer by atmospheric suspensoids (and, to slight extent, by air molecules) lying in the observer's cone of vision. That is, air light reaches the eye in the same manner that diffuse sky radiation reaches the earth's surface.
Air light is not be confused with airglow .
air lock
   (NASA SP-7, 1965)
1. A stoppage or diminution of flow in a fuel system, hydraulic system, or the like, caused by a pocket of air or vapor. 2. A chamber capable of being hermetically sealed that provides for passage between two places of different pressure, as between an altitude chamber and the outside atmosphere.
air locks
   (NASA Thesaurus)
A stoppage or diminution of flow in a fuel system, hydraulic system, or the like, caused by pockets of air or vapor. Also chambers capable of being hermetically sealed that provide for passage between two places of different pressure as between an altitude chamber and the outside atmosphere.
air masses
   (NASA Thesaurus)
Large widespread volumes of air having particular characteristics of temperature and moisture content that were acquired at its source region and are modified as they move away from their source.
air navigation
   (NASA Thesaurus)
The art, science, or action of plotting and directing the course of an aircraft through the air from one place to another.
air pollution
   (NASA Thesaurus)
The presence of unwanted material in the air. The term "unwanted material" here refers to material in sufficient concentrations, present for a sufficient time, and under circumstances to interfere significantly with comfort, health, or welfare of persons, or with the full use and enjoyment of property. Used for atmospheric impurities.
air position indicator
   (NASA SP-7, 1965)
(abbr API)
An airborne computing system which presents a continuous indication of the aircraft position on the basis of aircraft heading, airspeed, and elapsed time.
air shower
   (NASA SP-7, 1965)
A grouping of cosmic-ray particles observed in the atmosphere; a cascade shower in the atmosphere. Also called shower .
Primary cosmic rays slowed down in the atmosphere emit bremsstrahlung photons of high energy. Each of these photons produces secondary electrons which generate more photons and the process continues until the available energy is absorbed.
air slew missiles
   (NASA Thesaurus)
Solid propellant rockets utilizing thrust vector control.
air sounding
   (NASA SP-7, 1965)
The act of measuring atmospheric phenomena or determining atmospheric conditions at altitude, especially by means of apparatus carried by balloons or rockets. See sounding.
air start
   (NASA SP-7, 1965)
An act or instance of starting an aircraft's engine while in flight, especially a jet engine after flameout. Compare in-flight start, ground start.
air traffic control
   (NASA Thesaurus)
A service operated by approriate authority to promote the safe, orderly and expedious flow of air traffic.
air transportation
   (NASA Thesaurus)
The conveyance of cargo and passengers by means of airplanes, helicopters, and other airborne vehicles.
air vane
   (NASA SP-7, 1965)
A vane that acts in the air, as contrasted to a jet vane which acts within a jetstream. See control vane.
air vehicle
   (NASA SP-7, 1965)
= aircraft
air-space
   (NASA SP-7, 1965)
Of or pertaining to both the atmosphere and space.
Because this adjective is pronounced as the noun airspace is, it is subject to misunderstanding. Aerospace is commonly used instead.
Airborne Integrated Reconnaissance System
   (NASA Thesaurus)
Aerial reconnaissance system incorporating various modes of detection. Used for AIRS (reconnaissance sys).
airborne radar approach
   (NASA Thesaurus)
The use of airborne radar for helicopter approach control -- the radar cursor technique.
airbreather
   (NASA SP-7, 1965)
An aerodynamic vehicle propelled by fuel oxidized by intake from the atmosphere; an air breathing vehicle.
airbreathing
   (NASA SP-7, 1965)
Of an engine or aerodynamic vehicle, required to take in air for the purpose of combustion.
aircraft
   (NASA SP-7, 1965)
Any structure, machine, or contrivance, especially a vehicle, designed to be supported by the air, being borne up either by the dynamic action of the air upon the surfaces of the structure or object, or by its own buoyancy; such structures, machines, or vehicles collectively, as, fifty aircraft.
Aircraft, in its broadest meaning, includes fixed-wing airplanes, helicopters, gliders, airships, free and captive balloons, ornithopters, flying model aircraft, kites, etc., but since the term carries a strong vehicular suggestion, it is more often applied, or recognized to apply, only to such of these craft as are designed to support or convey a burden in or through the air.
aircraft communication
   (NASA Thesaurus)
The conveyance of information to or from aircraft by radio or other signals.
aircraft construction materials
   (NASA Thesaurus)
A general term designating the materials used in manufacturing an aircraft.
aircraft control
   (NASA Thesaurus)
To direct the movements of an aircraft with particular reference to changes in attitude and speed.
aircraft design
   (NASA Thesaurus)
The act of conceiving and planning the structure, systems, and performance characteristics of an aircraft vehicle or any other apparatus, machine or contrivance intended to be borne up either by dynamic action of the air upon the object`s surfaces, or by the object`s own buoyancy.
aircraft icing
   (NASA Thesaurus)
Accumulation of ice on aircraft external surfaces, propellers and engine inlets from freezing rain or flight through inclement weather.
aircraft instruments
   (NASA Thesaurus)
Any electronic or mechanically-based instrument or instrument system designed for detecting, measuring, displaying, recording, telemetering, processing, or analyzing different values or quantities encountered in the flight of an aircraft; often supporting the general control of the aircraft.
aircraft performance
   (NASA Thesaurus)
The manner or effectiveness with which an aircraft vehicle or any airborne structure, machine, or contrivance functions while in operation.
aircraft power supplies
   (NASA Thesaurus)
Electric power sources for the normal operation of aircraft.
aircraft rocket
   (NASA SP-7, 1965)
A rocket missile designed to be carried by, and launched from, an aircraft.
aircraft runup
   (NASA Thesaurus)
Final engine check prior to takeoff.
aircraft safety
   (NASA Thesaurus)
Techniques used to prevent aircraft failures or accidents; the degree to which an aircraft is free of the risk of malfunction or accidents.
aircraft spin
   (NASA Thesaurus)
A prolonged stall in fixed-wing aircraft characterized by a sustained spiral descent, usually with the nose down.
aircraft stability
   (NASA Thesaurus)
The property of an aircraft to maintain its attitude or to resist displacement, and if displaced, to develop forces and moments tending to restore the original condition.
airflow
   (NASA SP-7, 1965)
A flow or stream of air. An airflow may take place in a wind tunnel, in the induction system of an engine, etc., or a relative airflow can occur, as past the wing or other parts of a moving craft; a rate of flow, measured by mass or volume per unit of time. See flow.
airfoil
   (NASA Thesaurus / NASA SP-7, 1965)
A structure, piece, or body, originally likened to a foil or leaf in being wide and thin, designed to obtain a useful reaction on itself in its motion through the air.
airfoil oscillations
   (NASA Thesaurus)
Periodic motions experienced by airfoils in aerodynamic conditions.
airframe
   (NASA Thesaurus / NASA SP-7, 1965)
The assembled structural and aerodynamic components of an aircraft or rocket vehicle that support the different systems and subsystems integral to the video.
The word airframe, a carryover from aviation usage, remains appropriate for rocket vehicles since a major function of the airframe is performed during flight within the atmosphere. There is disagreement as to whether the nose cone and combustion chambers are included in the term airframe while they are attached to the vehicle.
airglow
   (NASA Thesaurus / NASA SP-7, 1965)
The quasi-steady radiant emission from the upper atmosphere as distinguished from the sporadic emission of the auroras.
Airglow is a chemiluminescence due primarily to the emission of the molecules O2 and N2, the radical OH, and the atoms O and Na. Emissions observed in airglow could arise from three-body atom collisions forming molecules, from two-body reactions between atoms and molecules, or from recombination of ions.
Historically, airglow has referred to visual radiation. Some recent studies use airglow to refer to radiation outside the visual range.
airport security
   (NASA Thesaurus)
Organization of trained security personnel, surveillance and screening devices, and procedures used for the protection of airport and airline property, aircraft, passengers, employees, and visitors from injury, air piracy, and other unauthorized acts.
airports
   (NASA Thesaurus)
An area of land or water that is used, or intended to be used, for the landing and takoff of aircraft, including buildings and facilities, if any.
airscoop
   (NASA SP-7, 1965)
A hood or open end of an air duct or a similar structure, projecting into the airstream about a vehicle in such a way as to utilize the motion of the vehicle in capturing air to be conducted to an engine, a ventilator, etc.
airships
   (NASA Thesaurus)
Propelled and steerable dirigibles dependent on gases for flotation. Used for aerostats and dirigibles.
airsickness
   (NASA SP-7, 1965)
Motion sickness occurring in flight.
airspace
   (NASA Thesaurus / NASA SP-7, 1965)
Specifically, the atmosphere above a particular portion of the earth, usually defined by the boundaries of an area on the surface projected upward.
Airspace is sometimes particularized by altitude, as the airspace above 20,000 feet.
airstream
   (NASA SP-7, 1965)
= airflow
Aitken dust counter
   (NASA SP-7, 1965)
An instrument developed by John Aitken for determining the dust content of the atmosphere. In operation, a sample of air is mixed, in an expandable chamber, with a larger volume of dust-free air containing water vapor. Upon a sudden expansion, the chamber cools adiabatically below its dewpoint, and the droplets form with the dust particles as nuclei (Aitken nuclei). A portion of these droplets settle on a ruled plate in the instrument and are counted with the aid of a microscope. Also called Aitken nucleus counter .
Aitken nuclei
   (NASA Thesaurus / NASA SP-7, 1965)
The microscopic particles in the atmosphere which serve as condensation nuclei for droplet growth during the rapid adiabatic expansion produced by an Aitken dust counter. These nuclei are both solid and liquid particles whose diameters are of the order of tenths of microns or even smaller.
The Aitken nuclei play an important role in atmospheric electrical processes, for they are the particles which capture (by adsorption or other surface electrical processes) small ions and thereby form large ions. In air containing large numbers of Aitken nuclei, the small ion population is small, the large ion population is large, and the air conductivity is low.
Aitken nucleus counter
   (NASA SP-7, 1965)
= Aitken dust counter.
akermanite
   (NASA Thesaurus)
A mineral of the melilite group. It is isomorphous with gehlenite.
Alais meteorite
   (AS&T Dictionary)
A carbonaceous chondrite specimen which fell to earth in France in 1806. It weighed 0.3 grams.
albedo
   (Solar System Dynamics Glossary - JPL)
Geometric albedo is the ratio of a body's brightness at zero phase angle to the brightness of a perfectly diffusing disk with the same position and apparent size as the body.
albedo
   (NASA Thesaurus / NASA SP-7, 1965)
The ratio of the amount of electromagnetic radiation reflected by a body to the amount incident upon it, often expressed as a percentage, as, the albedo of the earth is 34% . Compare Bond albedo.

The concept defined above is identical with reflectance. However, albedo is more commonly used in astronomy and meteorology and reflectance in physics.
Albedo is sometimes used to mean the flux of the reflected radiation as, the earth albedo is 0.64 calorie per square centimeter. This usage should be discouraged.
The albedo is to be distinguished from the spectral reflectance which refers to one specific wavelength (monochromatic radiation).
Usage varies somewhat with regard to the exact wavelength interval implied in albedo figures; sometimes just the visible portion of the spectrum is considered, sometimes the totality of wavelengths in the solar spectrum.
albedo neutrons
   (AS&T Dictionary)
Secondary neutrons ejected (along with other particles) in the collision of cosmic ray ions with particles of the upper atmosphere. See neutron albedo.
albedometer
   (NASA SP-7, 1965)
An instrument used for the measurement of the reflecting power, the albedo, of a surface. A pyranometer adapted for the measurement of radiation reflected from the earth's surface is sometimes employed as an albedometer.
alcator
   (Plasma Physics and Fusion Energy Glossary)
Name given to a set of tokamaks designed and built at MIT; these machines are distinguished by high magnetic fields with relatively small diameters. The high magnetic field helps create plasmas with relatively high current and particle densities. The current incarnation is Alcator C-mod, and is described further in Section 5. Alcator C was donated to LLNL for use as the Microwave Tokamak eXperiment (MTX), now shut down.
alcator scaling
   (Plasma Physics and Fusion Energy Glossary)
A proposed empirical law in which the energy confinement time is proportional to the product of the average density and the square of the plasma radius.
aldehydes
   (NASA Thesaurus)
Carbonyl groups to which a hydrogen atom is attached; the first stage of an alcohol; - CHO.
alexandrite
   (NASA Thesaurus)
A transparent variety of chrysoberl that has a grass-green or emerald green color in daylight and wine-red to brownish-red color by transmitted or incandescent artificial light.
Alford loop
   (NASA SP-7, 1965)
A multielement antenna, having approximately equal and in-phase currents uniformly distributed along each of its peripheral elements, producing a substantially circular radiation pattern in the plane of polarization.
Alfvén ion cyclotron instability
   (Plasma Physics and Fusion Energy Glossary)
(AIC) An electromagnetic microinstability near the ion cyclotron frequency; driven by the ion loss cone in a mirror device.
Alfvén layer
   (AS&T Dictionary)
Term introduced in 1969 by Schield, Dessler and Freeman, to describe the region in the nightside magnetosphere where region 2 Birkeland currents apparently originate. Magnetospheric plasma must be (to a high degree of approximation) charge neutral, with equal densities of positive ion charge and negative electron charge. If such plasma convects earthward under the influence of an electric field, as long as the magnetic field stays constant (a fair approximation in the distant tail) charge neutrality is preserved.
Near Earth, however, the magnetic field begins to be dominated by the dipole-like form of the main field generated in the Earth's core, and the combined drift due to both electric and magnetic fields tends to separate ions from electrons, steering the former to the dusk side of earth and the latter to the dawn side. This creates Alfvén layers, regions where those motions fail to satisfy charge neutrality. Charge neutrality is then restored by electrons drawn upwards as the downward region 2 current, and electrons dumped into the ionosphere (plus some ions drawn up) to create the corresponding upward currents.
Alfvén Mach number
   (NASA SP-7, 1965)
The ratio of the local flow velocity to the local Alfvén speed. See Alfvén wave.
Alfvén speed
   (NASA SP-7, 1965)
The speed at which Alfvén waves are propagated along the magnetic field.
For a perfectly conducting fluid with a mass density of 1 kilogram per cubic meter in a magnetic field of 10,000 gauss, the Alfvén speed is about 1,000 meters per second while the speed of sound in air is about 300 meters per second.
Alfvén velocity
   (Plasma Physics and Fusion Energy Glossary)
Phase velocity of the Alfvén wave; equal to the speed of light divided by the square root of (1 plus the ratio of the plasma frequency to the cyclotron frequency for a given species). i.e., Va = c / SQRT(1 + plasma freq. / cyclotron freq.)
Alfvén wave
   (Plasma Physics and Fusion Energy Glossary)
Transverse electromagnetic waves that are propagated along lines of magnetic force in a plasma. The waves have frequency significantly less than the ion cyclotron frequency, and are characterized by the fact that the field lines oscillate (wiggle) with the plasma. The propagation velocity depends on the particle density and the strength of the magnetic field.
Alfvén wave
   (NASA SP-7, 1965)
A transverse wave in a magnetohydrodynamic field in which the driving force is the tension introduced by the magnetic field along the lines of force. Also called magnetohydrodynamic wave .
The dynamics of such waves are analogous to those in a vibrating string, the phase speed C being given by c squared equals mu h squared over four pi rho where mu is the permeability; H is the magnitude of the magnetic field; and rho is the fluid density.
alga (plural, algae)
   (NASA Thesaurus / NASA SP-7, 1965)
Any plants of a group of unicellular and multicellular primitive organisms that include the Chlorella, Scenedesmus, and other genera.
The green algae and blue-green algae, for example, provide a possible means of photosynthesis in a closed ecological system, also a source of food.
algorism
   (NASA SP-7, 1965)
The art or system of calculating with any species of notation, as in arithmetic with nine figures and a zero. Also called algorithm.
Different algorisms have been used in the design of computing machines.
algorithm
   (NASA Thesaurus / NASA SP-7, 1965)
1. A special mathematical procedure for solving a particular type of problem.
2. = algorism.
alidade
   (NASA SP-7, 1965)
That part of an optical measuring instrument comprising the optical system, indicator, vernier, etc.
In modern practice the term is used principally to refer to a telescope mounted over a compass or compass repeater to facilitate observation of bearings, and to a surveying instrument consisting of a telescope mounted over a compass rose, for measuring directions.
alkali metal
   (NASA Thesaurus / NASA SP-7, 1965)
A metal in group IA of the periodic system; namely, lithium, sodium, potassium, rubidium, cesium, and francium. Alkali metals have been considered as coolants (in liquid state) for nuclear reactors for spacecraft. See liquid-metal corrosion.
alkali vapor lamps
   (NASA Thesaurus)
Lamps in which light is produced by an electric discharge between electrodes in an alkali vapor at low or high pressures.
alkalinity
   (NASA Thesaurus)
The state of being alkaline.
all burnt
   (NASA SP-7, 1965)
The time at which a rocket consumes its propellants. See burnout, note.
all sky camera
   (AS&T Dictionary)
A camera (photographic, or more recently, TV) viewing the reflection of the night sky in a convex mirror. The image is severely distorted, but encompasses the entire sky and is thus very useful for recording the distribution of auroral arcs in the sky.
all-inertial guidance
   (NASA SP-7, 1965)
The guidance of a rocket vehicle entirely by use of inertial devices; the equipment used for this.
Allende meteorite
   (AS&T Dictionary)
One of any carbonaceous chondrite specimens found in the Allende strewn field named after the nearby town of Pueblito de Allende, Chihuahua State, Mexico. The Allende meteor fell at 1:05 AM on February 8, 1969 and is calculated to have weighed several tons. The resulting meteorites are of the CV3 letter designation.
alloy
   (NASA Thesaurus / NASA SP-7, 1965)
A substance having metallic properties and being composed of two or more chemical elements of which at least one is an elemental metal.
alloying element
   (NASA SP-7, 1965)
An element added to a metal to effect changes in properties and which remains within the metal.
alluvium
   (NASA Thesaurus)
Soil, the constituents of which have been transported in suspension by flowing water and subsequently deposited by sedimentation.
almucantar
   (NASA SP-7, 1965)
= parallel of altitude.
Aloha system
   (NASA Thesaurus)
A multiple random access communications scheme in which there is a nonfixed allocation of channel capacity, so that the channel is available to any terminal whenever it has a packet ready for transmission.
alpha decay
   (NASA Thesaurus / NASA SP-7, 1965)
The radioactive transformation of a nuclide by alpha-particle emission. Also called alpha disintegration.
The decay product is the nuclide having a mass number four units smaller and an atomic number two units smaller than the original nuclide.
alpha disintegration
   (NASA SP-7, 1965)
= alpha decay
Alpha emission
   (Plasma Physics and Fusion Energy Glossary)
Form of nuclear decay where the nucleus emits an alpha particle (see entry below).
Alpha Magnetic Spectrometer
   (AS&T Dictionary)
A magnetic spectrometer, based on a large permanent magnet and a very precise particle tracker consisting of silicon microstrip detectors with antimatter/matter sensitivity of one part in 1010. It will operate in space at an altitude of about 430 km. It is designed to detect dark matter, antimatter, and matter not previously detected in the universe.
alpha particle
   (NASA Thesaurus / NASA SP-7, 1965)
A positively charged particle emitted from the nuclei of certain atoms during radioactive disintegration. The alpha particle has an atomic weight of 4 and a positive charge equal in magnitude to 2 electronic charges; hence it is essentially a helium nucleus (helium atom stripped of its two planetary electrons). Compare beta particle, gamma ray.
alpha particle
   (Plasma Physics and Fusion Energy Glossary)
The nucleus of a Helium-4 atom; is a typical product of fusion reactions; also released in various nuclear decay processes. Alpha particles readily grab electrons from other sources, becoming neutral helium; even energetic alpha particles are easily stopped by thin barriers (sheets of paper, dead layers of skin, etc.), so that as a radiological hazard alpha particles are only dangerous if they are generated inside one's body (where the skin cannot protect tissue from damage). Alpha particles are common products in fusion reactions between light elements.
alpha ray
   (NASA SP-7, 1965)
A stream of alpha particles.
alphanumeric (alphabet plus numeric)
   (NASA SP-7, 1965)
Including letters and digits.
alphanumeric characters
   (NASA Thesaurus)
Characters in a set that contain both letters and digits, but they usually also contain other characters such as punctuation symbols.
Alpine meteorology
   (NASA Thesaurus)
Wind, precipitation, atmospheric physics, and other climatological phenomena peculiar to the Alps and/or other similar mountainous areas.
ALT
   (Space Flight Glossary - JPL)
Altitude.
ALT
   (Space Flight Glossary - JPL)
Altimetry data.
alternating current
   (Plasma Physics and Fusion Energy Glossary)
(AC) Electrical current which alternates direction periodically. (For instance, household electric current is AC alternating at 60 oscillations/sec (60 Hertz) in the United States, and 50 Hertz in many other countries.)
altimeter
   (NASA Thesaurus / NASA SP-7, 1965)
An instrument for measuring height above a reference datum; specifically, an instrument similar to an aneroid barometer that utilizes the change of atmospheric pressure with altitude to indicate the approximate elevation above a given point or plane used as a reference. See absolute altimeter, pressure altimeter, radio altimeter.
altitude
   (NASA Thesaurus / NASA SP-7, 1965)
(symbol h)
1. In astronomy, angular displacement above the horizon; the arc of a vertical circle between the horizon and a point on the celestial sphere, measured upward from the horizon.
Angular displacement below the horizon is called negative altitude or dip. See horizon system.
2. Height, especially radial distance as measured above a given datum, as average sea level. See absolute altitude, true altitude.
In space navigation altitude designates distance from the mean surface of the reference body as contrasted to distance, which designates distance from the center of the reference body.
altitude acclimatization
   (NASA Thesaurus / NASA SP-7, 1965)
A physiological adaptation to reduced atmospheric and oxygen pressure.
altitude chamber
   (NASA SP-7, 1965)
A chamber within which the air pressure, temperature, etc., can be adjusted to simulate conditions at different altitudes; used for experimentation and testing.
altitude circle
   (NASA SP-7, 1965)
= parallel of altitude
altitude difference
   (NASA SP-7, 1965)
In navigation, the difference between computed and observed altitudes, or between precomputed and sextant altitudes. It is labeled T (toward) or A (away) as the observed (or sextant) altitude is greater or smaller than the computed (or precomputed) altitude. Also called altitude intercept, intercept .
altitude intercept
   (NASA SP-7, 1965)
= altitude difference
Often shortened to intercept.
altitude sickness
   (NASA Thesaurus / NASA SP-7, 1965)
In general, any sickness brought on by exposure to reduced oxygen tension and barometric pressure.
Many writers have proposed specific definitions for this term but the definitions are highly variable.
altitude wind tunnel
   (NASA SP-7, 1965)
A wind tunnel in which the air pressure, temperature, and humidity can be varied to simulate conditions at different altitudes.
In an altitude wind tunnel for testing engines, provision is made for exchanging fresh air for exhaust-laden air during operation.
aluminides
   (NASA Thesaurus)
Intermetallic compounds of aluminum and a transition metal.
aluminum arsenides
   (NASA Thesaurus)
Binary compounds of aluminum with negative, trivalent arsenic.
aluminum boron composites
   (NASA Thesaurus)
Structural materials composed of aluminum alloys reinforced with boron fibers (filaments).
aluminum gallium arsenides
   (NASA Thesaurus)
Compounds exhibiting characteristics suitable for use in laser devices, light-emitting diodes, solar cells, etc. Used for AlGaAs.
aluminum graphite composites
   (NASA Thesaurus)
Structural materials composed of aluminum alloys reinforced with graphite.
aluminum-lithium alloys
   (NASA Thesaurus)
Light alloys consisting primarily of aluminum and lithium.
alveolar air
   (NASA Thesaurus / NASA SP-7, 1965)
The respiratory air in the alveoli (air sacs) deep within the lungs.
alveolar oxygen pressure
   (NASA SP-7, 1965)
The oxygen pressure in the alveoli. The value is about 105 millimeters of mercury.
alveoli
   (NASA Thesaurus / NASA SP-7, 1965)
The terminal air sacs deep within the lungs. The inhaled oxygen diffuses across the thin alveolar membranes (the walls of the air sacs) into the blood stream, and at the same time carbon dioxide diffuses from the blood into the alveoli and is exhaled through the lungs.
am
   (Space Flight Glossary - JPL)
Attometer (10-18 meter).
AM
   (Space Flight Glossary - JPL)
Ante meridiem (Latin: before midday), morning.
AM (abbr)
   (NASA SP-7, 1965)
= amplitude modulation.
Amalthea
   (NASA Thesaurus)
Innermost satellite of Jupiter.
AMBAL
   (Plasma Physics and Fusion Energy Glossary)
An ambipolar trap (tandem mirror) located at Novosibirsk in Russia.
ambient
   (NASA SP-7, 1965)
(symbol alpha lower case, used as a subscript)
Surrounding; especially, of or pertaining to the environment about a flying aircraft or other body but undisturbed or unaffected by it, as in ambient air, or ambient temperature.
ambient noise
   (NASA SP-7, 1965)
The pervasive noise associated with a given environment, being usually a composite of sounds from sources both near and distant.
ambient pressure
   (AS&T Dictionary)
Pressure of surrounding medium. Used for environmental pressure.
ambient temperature
   (NASA Thesaurus)
Temperature of surrounding medium. Used for environmental temperature.
ambiguity
   (NASA SP-7, 1965)
In navigation, the condition arising when a given set of observations defines more than one point, direction, line of position, or surface of position.
ambipolar diffusion
   (Plasma Physics and Fusion Energy Glossary)
Diffusion process in which buildup of spatial charge creates electric fields which cause electrons and ions to leave the plasma at the same rate. (Such electric fields are self-generated by the plasma and act to preserve charge neutrality.)
ambipolar field
   (AS&T Dictionary)
An electric field amounting to several volts, maintaining charge neutrality in the ionosphere, in the region above the E-layer where collisions are rare. If that field did not exist, ions and electrons would each set their own scale height--small for the ions (mostly O+), large for the fast electrons--and densities of positive and negative charge would not match. The ambipolar field pulls electrons down and ions up, assuring charge neutrality by forcing both scale heights to be equal.
American Ephemeris and Nautical Almanac
   (NASA SP-7, 1965)
An annual publication of the U.S. Naval Observatory, containing elaborate tables of the predicted positions of various celestial bodies and other data of use to astronomers and navigators.
Beginning with the editions for 1960, The American Ephemeris and Nautical Almanac issued by the Nautical Almanac Office, United States Naval Observatory, and the Astronomical Ephemeris issued by H.M. Nautical Almanac Office, Royal Greenwich Observatory, were unified. With the exception of a few introductory pages, the two publications are identical; they are printed separately in the two countries, from reproducible material prepared partly in the United States of America and partly in the United Kingdom.
American Nautical Almanac
   (NASA SP-7, 1965)
See Nautical Almanac.
ammeters
   (NASA Thesaurus)
An instrument for measuring the magnitude of an electric current.
AMMOS
   (Space Flight Glossary - JPL)
Advanced Multimission Operations System.
Amor asteroid
   (NASA Thesaurus)
One group of Earth-approaching asteroids with orbits between the planets Mars and Jupiter. Used for Minor Planet 1221.
ampere
   (NASA SP-7, 1965)
(abbr A)
The unit of electric current; the constant current which, if maintained in two straight, parallel conductors of infinite length, of negligible circular cross sections, and placed 1 meter apart in a vacuum will produce between these conductors a force equal to 2*10-7 newtons per meter of length.
Ampere's law
   (Plasma Physics and Fusion Energy Glossary)
General equation in electromagnetism relating the magnetic field and the currents generating it. The various forms of the equation can be found in an introductory electromagnetism text.
ampere, kiloampere, megampere:
   (Plasma Physics and Fusion Energy Glossary)
The standard unit for measuring the strength of an electric current representing the flow of one coulomb of electricity per second. 1 kiloampere = 1000 amperes; 1 megampere = 1,000,000 amperes. Common abbreviations: A, amps, kiloamps, megamps, kA, MA
amphiboles
   (NASA Thesaurus)
A group of dark, rock-forming, ferromagnesian silicate minerals closely related in crystal form and composition.
Amphitrite asteroid
   (AS&T Dictionary)
An asteroid discovered in 1854 by A. Marth with an orbit of 2.55 astronomical units around the Sun and a diameter of 240 km.
amplidyne
   (NASA SP-7, 1965)
A special type of direct current generator used as a power amplifier in which the output voltage responds to changes in field excitation; used extensively in servo systems.
amplifier
   (NASA Thesaurus / NASA SP-7, 1965)
A device which enables an input signal to control a source of power, and thus is capable of delivering at its output an enlarged reproduction of the essential characteristics of the signal.
Typical amplifying elements are electron tubes, transistors, and magnetic circuits.
amplitude
   (NASA Thesaurus / NASA SP-7, 1965)
1. The maximum value of the displacement of a wave or other periodic phenomenon from a reference position.
2. Angular distance north or south of the prime vertical; the arc of the horizon, or the angle at the zenith between the prime vertical and a vertical circle, measured north or south from the prime vertical to the vertical circle.
The term is customarily used only with reference to bodies whose centers are on the celestial horizon, and is prefixed E or W, as the body is rising or setting, respectively; and suffixed N or S to agree with the declination. The prefix indicates the origin, and the suffix indicates the direction of measurement. Amplitude is designated as true, magnetic, compass, or grid as the reference direction is true, magnetic, compass, or grid east or west, respectively.
amplitude modulation
   (NASA Thesaurus / NASA SP-7, 1965)
1. In general, modulation in which the amplitude of a wave is the characteristic subject to variation.
2. Specifically, in telemetry those systems of modulation in which each component frequency, f, of the transmitted intelligence produces a pair of sideband frequencies at carrier frequency plus f and carrier minus f.
In special cases: (a) the carrier may be suppressed, (b) either the lower or upper sets of sideband frequencies may be suppressed; (c) the lower set of sideband frequencies may be produced by one or more channels of information and the upper set of sideband frequencies may be produced by one or more other channels of information; (d) the carrier may be transmitted without intelligence carrying sideband frequencies.
amplitude-modulated indicator
   (NASA SP-7, 1965)
One of two general classes of radar indicators, in which the sweep of the electron beam is deflected vertically or horizontally from a base line to indicate the existence of an echo from a target. The amount of deflection is usually a function of the echo signal strength. Also called deflection-modulated indicator . Compare intensity modulated indicator.
ampoules
   (NASA Thesaurus)
Glass containers designed to be filled and sealed by fusion of the glass neck.
AMPTE (satellites)
   (AS&T Dictionary)
The AMPTE (Active Magnetospheric Particle Tracer Explorer) mission was designed to study the access of solar-wind ions to the magnetosphere, the convective-diffusive transport and energization of magnetospheric particles, and the interactions of plasmas in space. The mission consisted of three spacecraft: the Charge Composition Explorer (CCE) ; the Ion Release Module (IRM), which provided multiple ion releases in the solar wind, the magnetosheath, and the magnetotail, with in situ diagnostics of each; and the United Kingdom Subsatellite (UKS), which used thrusters to keep station near the IRM to provide two-point local measurements. It was launched on a Delta rocket August 16, 1984.
AMR
   (NASA SP-7, 1965)
= Atlantic Missile Range (definition 4)
anabranch
   (Glossary of Hydrologic Terms - NOAA)
A diverging branch of a river which re-enters the main stream, characteristic of braided streams.
anacoustic zone
   (NASA SP-7, 1965)
The region above an altitude of about 100 miles where the distance between the air molecules is greater than the wavelength of sound, and sound waves can no longer be propagated.
analog
   (NASA SP-7, 1965)
In computers, pertaining to the use of physical variables such as voltage, distance, rotation, etc. To represent numerical variable as in analog computer, analog output . Compare digital.
analog computer
   (NASA Thesaurus / NASA SP-7, 1965)
A computing machine working on the principle of measuring, as distinguished from counting, in which the input data is analogous to a measurement continuum, such as linear lengths, voltages, resistances, etc., which can be manipulated by the computer.
Analog computers range in complexity from a slide rule to electrical computers used for solving mathematical problems.
analog output
   (NASA SP-7, 1965)
Transducer output in which the amplitude is continuously proportional to a function of the stimulus. Distinguished from digital output .
analog to digital conversion
   (NASA SP-7, 1965)
A process by which a sample of analog information is transformed into a digital code.
analog to digital converter
   (NASA SP-7, 1965)
(abbr ADC)
A device which will convert an analog voltage sample to an equivalent digital code of some finite resolution. Also called digitizer, encoder .
analog to digital converters
   (NASA Thesaurus)
Devices for converting non-digital information into digits. Used for digitizers.
analysis (mathematics)
   (NASA Thesaurus)
That part of the field of mathematics which arises from the calculus and which deals primarily with functions.
analysis of variance
   (NASA Thesaurus)
A systematic statistical procedure for determining the sources and the magnitudes of the errors present in a measurement process, and for assessing the significance of differences between materials, processes, or test methods under study.
analytical photography
   (NASA SP-7, 1965)
Photography, either motion picture or still, accomplished to determine (by qualitative, quantitative, or any other means) whether a particular phenomenon does or does not occur. See technical photography.
Differs from metric photography in that measurements are not a prime requisite.
anchor ice
   (Glossary of Hydrologic Terms - NOAA)
Submerged frazil ice attached or anchored to the river bottom, irrespective of its formation.
anchor ice dam
   (Glossary of Hydrologic Terms - NOAA)
An accumulation of anchor ice which acts as a dam and raises the water level.
AND
   (NASA SP-7, 1965)
In Boolean algebra, the operation of intersection.
AND circuit
   (NASA SP-7, 1965)
= AND gate.
AND gate
   (NASA SP-7, 1965)
A circuit or device used in computers whose output is energized only when every input is in its prescribed state. It performs the logical function of the AND, the Boolean operation of intersection. Also called intersector , AND circuit .
And, Andr.
   (NASA SP-7, 1965)
International Astronomical Union abbreviations for Andromeda . See constellation.
AND-NOT gate
   (NASA SP-7, 1965)
= exclusive OR circuit.
andesite
   (Photoglossary of Volcanic Terms - USGS)
Andesite is a black to gray rock with between 53 and 63 weight percent silica (SiO2). Common minerals in andesite include plagioclase feldspar, pyroxene, and iron oxide. Andesites are very common on stratovolcanoes, where they form both thick lava flows and moderate-sized explosive eruptions of tephra. Andesites erupt at temperatures between 900 and 1100 Centigrade.
andesite
   (NASA Thesaurus)
Volcanic rock composed essentially of andesine and one or more mafic constituents.
Andromeda constellation
   (AS&T Dictionary)
A group of stars visible in the Northern Hemisphere from June through February. In the sky, it is located south of the constellation Cassiopeia and west of the constellation Perseus. Within the same field of view from earth, the Andromeda galaxy can also be seen.
Andromeda constellation
   (NASA SP-7, 1965)
(abbr And, Andr).
See constellation.
Andromeda galaxy
   (AS&T Dictionary)
A multiple ringed galaxy with the Messier catalog number of 31. It is the most distant object visible from earth with the naked eye, at approximately two million light years.
anechoic chambers
   (NASA Thesaurus)
Enclosures especially designed with boundaries that absorb sufficiently well the sound incident thereon to create an essentially field-free condition in the frequency ranges of interest.
anelasticity
   (AS&T Dictionary)
The property of a substance having no definite relationship between stress and strain.
anemometers
   (NASA Thesaurus)
Instruments used to measure the speed of air currents, usually measured from the rotation of wind drivin cups or from wind pressure through a tube pointed into the wind.
aneroid
   (NASA SP-7, 1965)
A thin, disk-shaped box or capsule, usually metallic, partially evacuated of air and sealed, which expands and contracts with changes in atmospheric or gaseous pressure.
The aneroid is the sensing and actuating element in various meters or gages, such as barometers, altimeters, manifold-pressure gages, etc; it is also the triggering or operating element in various automatic mechanisms. A device similar to an aneroid, but open to outside pressures, such as the capsule in an airspeed indicator, is not commonly called an aneroid .
aneutronic fuels
   (Plasma Physics and Fusion Energy Glossary)
Advanced fusion fuels which would not produce fusion neutrons.
angel
   (NASA SP-7, 1965)
A radar echo caused by a physical phenomenon not discernible to the eye.
Angels are usually coherent echoes and sometimes of great signal strength (up to 40 decibels above the noise level). They have been ascribed to insects flying through the radar beam, but have also been observed under atmospheric conditions which indicate there must be other causes. Studies indicate that a fair portion of them are caused by strong temperature or moisture gradients, or both, such as might be found near the boundaries of bubbles of especially warm or moist air (see blob). They frequently occur in shallow layers at or near temperature inversions within the lowest few thousand feet of the atmosphere.
angels (radar)
   (NASA Thesaurus)
Echos of false radar targets caused by atmospheric inhomogeneity, atmospheric refraction, insects, birds, or unknown phenomena.
angle
   (NASA SP-7, 1965)
The inclination to each other of two intersecting lines, measured by the arc of a circle intercepted between the two lines forming the angle, the center of the circle being the point of intersection.
An acute angle is less than 90°; a right angle 90 °; an obtuse angle, more than 90° but less than 180 °; a straight angle, 180°; a reflex angle, more than 180° but less than 360°; a perigon, 360°. Any angle not a multiple of 90° is an oblique angle. If the sum of two angles is 90°, they are complementary angles; if 180°, supplementary angles; if 360°, explementary angles. Two adjacent angles have a common vertex and lie on opposite sides of a common side. A dihedral angle is the angle between two intersecting planes. A spherical angle is the angle between two intersecting great circles.
angle modulation
   (NASA SP-7, 1965)
Modulation in which the angle of a sine-wave carrier is the characteristic varied from its normal value.
Phase and frequency modulation are particular forms of angle modulation.
angle of arrival
   (NASA SP-7, 1965)
A measure of the direction of propagation of electromagnetic radiation upon arrival at a receiver (most commonly used in radio). It is the angle between the plane of the phase front and some plane of reference, usually the horizontal, at the receiving antenna. This angle is a function of the index of refraction gradient of the medium through which the energy is traveling, and the relative positions of the transmitter and receiver. Compare angle of incidence.
Angles of arrival can be measured for both the direct and reflected components of a wave using a multiple-antenna receiving system called an interferometer .
angle of attack
   (NASA Thesaurus / NASA SP-7, 1965)
The angle between a reference line fixed with respect to an airframe and a line in the direction of movement of the body.
angle of climb
   (NASA SP-7, 1965)
The angle between the flight path of a climbing vehicle and the local horizontal.
angle of depression
   (NASA SP-7, 1965)
The angle in a vertical plan between the local horizontal and a descending line. Also called depression angle . See angle of elevation.
angle of descent
   (NASA SP-7, 1965)
The angle between the flight path of a descending vehicle and the local horizontal.
angle of deviation
   (NASA SP-7, 1965)
The angle through which a ray is bent by refraction.
angle of elevation
   (NASA SP-7, 1965)
The angle in a vertical plane between the local horizontal and an ascending line, as from an observer to an object. Also called elevation angle.
A negative angle of elevation is usually called an angle of depression.
angle of incidence
   (NASA SP-7, 1965)
1. The angle at which a ray of energy impinges upon a surface, usually measured between the direction of propagation of the energy and a perpendicular to the surface at the point of impingement, or incidence. Compare angle of arrival. See also angle of reflection, angle of refraction.
In some cases involving radio waves, the angle of incidence is measured relative to the surface.
2. = angle of attack. (British usage).
angle of minimum deviation
   (NASA SP-7, 1965)
See minimum deviation.
angle of pitch
   (NASA SP-7, 1965)
1. The angle, as seen from the side, between the longitudinal body axis of an aircraft or similar body and a chosen reference line or plane, usually the horizontal plane. This angle is positive when the forward part of the longitudinal axis is directed above the reference line.
2. Same as blade angle.
angle of reflection
   (NASA SP-7, 1965)
The angle at which a reflected ray of energy leaves a reflecting surface, measured between the direction of the outgoing ray and a perpendicular to the surface at the point of reflection. Compare angle of incidence.
In some cases involving radio waves, the angle of reflection is measured relative to the surface.
angle of refraction
   (NASA SP-7, 1965)
The angle at which a refracted ray of energy leaves the interface at which the refraction occurred, measured between the direction of the refracted ray and perpendicular to the interface at the point of refraction.
angle of roll
   (NASA SP-7, 1965)
The angle that the lateral body axis of an aircraft or similar body makes with a chosen reference plane in rolling; usually the angle between the lateral axis and a horizontal plane. The angle of roll is considered positive if the roll is to starboard.
angle of yaw
   (NASA SP-7, 1965)
The angle, as seen from above, between the longitudinal body axis of an aircraft, rocket, or the like and a chosen reference direction. This angle is positive when the forward part of the longitudinal axis is directed to starboard. Also called yaw angle .
angles (geometry)
   (NASA Thesaurus)
The inclination to each other of two intersecting lines, measured by the arc of a circle intercepted between the two lines forming the angle, the center of the circle being the point of intersection.
angstrom
   (Solar Physics Glossary - NASA GSFC)
Abbreviated Å. A unit of length equal to 10-8 cm (one-hundredth of a millionth of a centimeter). An Angstrom is on the order of the size of an atom.
angstrom
   (NASA SP-7, 1965)
(abbr A, Å)
A unit of length, used chiefly in expressing short wavelengths. It equals 10-10 meter or 10-8 centimeters.
angular acceleration
   (NASA Thesaurus / NASA SP-7, 1965)
(symbol alpha lower case)
The rate of change of angular velocity.
angular distance
   (NASA SP-7, 1965)
1. The angular difference between two directions, numerically equal to the angle between two lines extending in the given directions.
2. The arc of the great circle joining two points, expressed in angular units.
3. Distance between two points, expressed in wavelengths at a specified frequency.
It is equal to the number of waves between the points multiplied by two pi if expressed in radians, or multiplied by 360° if measured in degrees.
angular frequency
   (NASA SP-7, 1965)
(symbol lower case omega)
The frequency of a periodic quantity expressed in radians per second. It is equal to the frequency in cycles per second multiplied by two pi. Also called circular frequency .
angular momentum
   (Imagine the Universe Dictionary - NASA GSFC)
A quantity obtained by multiplying the mass of an orbiting body by its velocity and the radius of its orbit. According to the conservation laws of physics, the angular momentum of any orbiting body must remain constant at all points in the orbit, i.e., it cannot be created or destroyed. If the orbit is elliptical the radius will vary. Since the mass is constant, the velocity changes. Thus planets in elliptical orbits travel faster at periastron and more slowly at apastron. A spinning body also possesses spin angular momentum.
angular momentum
   (NASA SP-7, 1965)
Quantity of rotational motion.
Linear momentum is the quantity obtained by multiplying the mass of a body by its linear speed. Angular momentum is the quantity obtained by multiplying the moment of inertia of a body by its angular speed. The momentum of a system of particles is given by the sum of the momentums of the individual particles which make up the system or by the product of the total mass of the system and the velocity of the center of gravity of the system. The momentum of a continuous medium is given by the integral of the velocity over the mass of the medium or by the product of the total mass of the medium and the velocity of the center of gravity of the medium.
See momentum
angular rate
   (NASA SP-7, 1965)
= angular speed, sense 1
angular resolution
   (NASA Thesaurus / NASA SP-7, 1965)
Specifically, the ability of a radar to distinguish between two targets solely by the measurement of angles.
It is generally expressed in terms of the minimum angle by which targets must be spaced to be separately distinguishable. See resolution.
angular speed
   (NASA SP-7, 1965)
1. Change of direction per unit time, as of a target on a radar screen. Also called angular rate .
2. = angular velocity.
angular velocity
   (NASA Thesaurus / NASA SP-7, 1965)
(symbol lower case omega)
The change of angle per unit time; specifically, in celestial mechanics, the change in angle of the radius vector per unit time.
Anik satellites
   (NASA Thesaurus)
A series of geostationary communication satellites operated by Telesat which is partly owned by the Canadian government and partly owned by private enterprise. The name "Anik" is derived from an Eskimo word meaning "brother." It was so designated because of its partial use in the Far North.
anisoplanatism
   (NASA Thesaurus)
In adaptive optics (AO) systems, a performance-degrading effect that arises whenever light from the wave-front sensor beacon and light from the target object sample different volumes of optical turbulence. This effect results in an increased value of the aperture-averaged residual phase variance after AO compensation, which causes an exponential decrease in system performance.
anisotropic
   (NASA SP-7, 1965)
Exhibiting different properties when tested along axes in different directions.
anisotropy
   (Plasma Physics and Fusion Energy Glossary)
Term used to describe a medium whose characteristic properties vary with direction of travel through the medium. (e.g., velocity of light transmission, conductivity of heat or electric current, compressibility, etc.)
anisotropy
   (NASA Thesaurus)
Having different properties in different directions.
annealing
   (NASA Thesaurus / NASA SP-7, 1965)
Application of heat energy to a material cooling at a suitable rate to: relieve stresses, change certain properties, improve machinability, etc., or for realignment of atoms in a distorted crystal lattice as caused, for example, by radiation damage.
annual flood
   (Glossary of Hydrologic Terms - NOAA)
The maximum discharge peak during a peak during a given water year.
annual parallax.
   (NASA SP-7, 1965)
See parallax.
annular
   (NASA SP-7, 1965)
Pertaining to an annulus or ring; ring shaped.
annular ducts
   (NASA Thesaurus)
Ring-shaped openings for the passage of fluids (gases, etc.) designed for optimum aerodynamic flow properties for the application involved.
annular eclipse
   (NASA SP-7, 1965)
An eclipse in which a thin ring of the source of light appears around the obscuring body.
annular suspension and pointing system
   (NASA Thesaurus)
In the Shuttle era, high accuracy pointing and stabilization of an experiment payload.
anode
   (NASA Thesaurus / NASA SP-7, 1965)
The positive pole or electrode of any electron emitter, such as an electron tube or an electric cell.
The negative pole or electrode is called a cathode.
anodic stripping
   (NASA Thesaurus)
The removal of metal coatings.
anodizing
   (NASA Thesaurus)
An electrolytic oxidation process in which the surface of a metal, when anodic, is converted to a coating having desirable protective, decorative, or functional properties.
anomalies
   (NASA Thesaurus)
In general, deviations from the norm.
anomalistic month
   (NASA SP-7, 1965)
The average period of revolution of the moon from perigee to perigee, a period of 27 days 13 hours 18 minutes 33.2 seconds.
anomalistic period
   (NASA SP-7, 1965)
The interval between two successive perigee passages of a satellite in orbit about a primary. Also called perigee-to-perigee period .
anomalistic year
   (NASA SP-7, 1965)
The period of one revolution of the earth about the sun from perihelion to perihelion; 365 days 6 hours 13 minutes 53.0 seconds in 1900 and increasing at the rate of 0.26 second per century.
anomalous diffusion
   (Plasma Physics and Fusion Energy Glossary)
Diffusion in most plasma devices, particularly tokamaks, is higher than what one would predict from understood causes. The observed, "typical" diffusion is referred to as "anomalous" because it has not yet been explained. Anomalous diffusion includes all diffusion which is not due to collisions and geometric effects. While such effects were not understood when the term was coined, and most still aren't, diffusion due to well-understood wave phenomena is still 'anomalous'. "Classical" diffusion and "Neo-classical" diffusion are the two well-understood diffusion theories, although neither is adequate to fully explain the observed "anomalous" diffusion.
anomalous dispersion
   (NASA SP-7, 1965)
Dispersion of electromagnetic radiation characterized by a decrease in refractive index with increase in frequency.
anomalous propagation
   (NASA SP-7, 1965)
The propagation of energy when it arrives at a destination via a path significantly different from the normally expected path.
The term is usually applied to the transmission of various forms of energy through the atmosphere when, in addition to the line-of-sight path, the energy is refracted by density discontinuities at one or more levels in atmosphere. Therefore, it propagates to a point that could not be reached via a line-of-sight path. In radio and radar studies, it refers to the abnormal refraction of a beam of radio energy, usually applied to superstandard propagation rather than to substandard propagation. In either case, anomalous propagation results from an unusual vertical distribution of temperature and moisture in the atmosphere.
The anomalous propagation of sound refers to the downward refraction of an oblique sound wave from an explosion, the refraction occurring in the region of increasing temperature with height in the lower mesosphere. The anomalous propagation of sound has been used as a method for determining upper air temperatures and winds.
anomaly
   (From Stargazers to Starships Glossary - GSFC)
In orbital motion, one of the angles which gauges the motion of a planet or satellite around its orbit, increasing by 360 degrees every revolution.
anomaly
   (NASA SP-7, 1965)
1. In general, a deviation from the norm.
2. In geodesy, a deviation of an observed value from a theoretical value, due to an abnormality in the observed quantity.
3. In celestial mechanics, the angle between the radius vector to an orbiting body from its primary (the focus of the orbital ellipse) and the line of apsides of the orbit, measured in the direction of travel, from the point of closest approach to the primary (perifocus).
The term defined above is usually called true anomaly v to distinguished it from the eccentric anomaly E which is measured at the center of the orbital ellipse to the projection of the body onto the auxiliary circle of the ellipse, or from the mean anomaly M which is what the true anomaly would become if the orbiting body had a uniform annular motion. The mean anomaly M can be computed by
M = n (t - T)
where n is mean motion; t is time of the computation; and T is time of perifocus. The eccentric anomaly E and the mean anomaly M are related by the Kepler equation
M = E - e sin E
where e is eccentricity of the ellipse. From E, the true anomaly v can be obtained by
tan v/2=[(1+e)/(1-e)]1/2 tan E/2.
anorthosite
   (NASA Thesaurus)
A group of essentially monomineralic plutonic igneous rocks composed almost entirely of plagioclass feldspar.
anoxaemia
   (NASA SP-7, 1965)
= hypoxaemia.
anoxia
   (NASA Thesaurus / NASA SP-7, 1965)
A complete lack of oxygen available for physiological use within the body. Compare hypoxia.
Anoxia is popularly used as a synonym for hypoxia . This usage should be avoided.
ansa
   (Planetary Rings Glossary - ARC)
An ansa is the portion of a ring that appears farthest from the disk of a planet in an image. This is the location in an image where we see the finest radial resolution on a ring. The word comes from the Latin word for "handle," since the earliest views of Saturn's rings suggested that the planet had two handles extending out on either side. The plural is either "ansae" or "ansas."
Ant, Antl.
   (NASA SP-7, 1965)
International Astronomical Union abbreviations for Antlia . See constellation.
antapex
   (NASA SP-7, 1965)
See solar apex.
Antarctic regions
   (NASA Thesaurus)
The areas surrounding and including the continent of Antarctica. Used for Antarctica.
antecedent precipitation index
   (Glossary of Hydrologic Terms - NOAA)
An index to soil moisture within a drainage basin. Abbreviated "API".
antecedent precipitation index method
   (Glossary of Hydrologic Terms - NOAA)
A statistical method to estimate the amount of surface runoff which will occur from a drainage basin from a given rain storm based on the antecedent precipitation index, physical characteristics of the drainage basin, time of year, storm duration, rainfall amount, and rainfall intensity.
antenna
   (NASA Thesaurus / NASA SP-7, 1965)
A conductor or system of conductors for radiating or receiving radio waves.
antenna array
   (NASA Thesaurus / NASA SP-7, 1965)
A system of antennas coupled together to obtain directional effects, or to increase sensitivity.
antenna effect
   (NASA SP-7, 1965)
A weakening of the effectiveness of the directional properties of a loop antenna by the capacitance of the loop to the ground. Also called height effect .
In usual direction-finding practice on ground waves, antenna effect would be manifested: (a) if in phase, by an angular displacement of the nulls from 180° displacement and (b), if in quandrature, by a residual signal obscuring the nulls. The in-phase effect is often used to eliminate the 180° ambiguity (i.e., to permit sense finding).
antenna field
   (NASA SP-7, 1965)
A group of antennas placed in a geometric configuration.
antenna gain
   (NASA SP-7, 1965)
See gain, sense 2(a).
antenna null
   (NASA SP-7, 1965)
See null.
antenna pair
   (NASA SP-7, 1965)
Two antennas located on a base line of accurately surveyed length.
antenna pattern
   (NASA SP-7, 1965)
= radiation pattern.
antenna temperature
   (NASA SP-7, 1965)
In radio astronomy, a measure of the power absorbed by the antenna. In an ideal, loss-free radio telescope, the antenna temperature is equal to the brightness temperature if the intensity of the received radiation is constant within the main lobe. If the angular dimension of the source is small compared to the main lobe, the antenna temperature is equal to the brightness temperature multiplied by the ratio of the solid angle subtended by the source to the effective solid angle of the antenna.
anthracite
   (NASA Thesaurus)
Coal of the highest metamorphic rank, in which fixed-carbon content is between 92 percent and 98 percent (on a dry, mineral-matter-free basis). It is hard and black, and has a semimetallic luster and semiconchoidal fracture. Anthracite ignites with difficulty and burns with a short blue flame, without smoke. Used for hard coal.
anthropogenic
   (Global Land Information System Glossary - USGS)
Relating to the scientific study of the origin of human beings and the results of their influence on nature.
anthropology
   (NASA Thesaurus)
The study of the interrelations of biological, cultural, geographical, and historical aspects of man.
anti-g suit
   (NASA SP-7, 1965)
= g-suit.
anti-Jovian
   (Galileo Project Glossary - JPL)
Used to refer to the side which is facing away from Jupiter.
anti-tail or anomalous tail
   (Comet Glossary - JPL)
When a comet's tail appears to be pointing toward the Sun, this is called an anti-tail or anomalous tail. In reality, the tail only appears to be pointing toward the Sun. To get an anti-tail, the comet must produce large ("heavy") dust particles. If this happens, these particles are left along the comet's orbit instead of being pushed away from the Sun and the comet's orbit by light pressure. Often dusty comets will produce particules of different sizes creating a fan-shaped appearance.
anticlines
   (NASA Thesaurus)
Geologic formations characterized by folds, the core of which contain stratigraphically older rocks; they convex upward. Used for anticlinoria.
anticyclones
   (AS&T Dictionary)
Atmospheric closed circulation, synoptic-scale weather features associated with sinking air and higher atmospheric pressure, and whose relative direction of rotation is clockwise in the Northern Hemisphere and counter-clockwise in the Southern Hemisphere.
anticyclonic
   (NASA SP-7, 1965)
Having a sense of rotation about the local vertical opposite to the rotation of the earth; that is, clockwise in the northern hemisphere, counterclockwise in the southern hemisphere, undefined at the equator; the opposite of cyclonic.
antifouling
   (NASA Thesaurus)
Measures taken to prevent corrosion or the accumulation of organic or other residues or growths on operating machanisms, especially in underwater environments.
antigravity
   (NASA Thesaurus / NASA SP-7, 1965)
A hypothetical effect that would arise from cancellation by some energy field of the effect of the central force field of the earth or other body.
Antigravity is common in science fiction but has not yet been reported in scientific literature.
antimatter
   (NASA SP-7, 1965)
Matter consisting of antiparticles.
antimisting fuels
   (NASA Thesaurus)
Fuels which have an additive to reduce misting and thus create safer fuels.
antinode
   (NASA Thesaurus / NASA SP-7, 1965)
1. Either of the two points on an orbit where a line in the orbit plane, perpendicular to the line of nodes, and passing through the focus, intersects the orbit.
2. A point, line, or surface in a standing wave where some characteristic of the wave field has maximum amplitude. Also called loop .
In sense 2, the appropriate modifier should be used before the word antinode to signify the type that is intended; e.g., displacement antinode, velocity antinode, pressure antinode.
antioxidants
   (NASA Thesaurus)
Compounding ingredients used to retard deterioration caused by oxidation.
antiparticle
   (NASA Thesaurus / NASA SP-7, 1965)
Any particle with a charge of opposite sign to the same particle in normal matters.
Thus, the proton has a positive charge; the antiproton, a negative charge. When a particle and its antiparticle collide, both may disappear with the creation of lighter particles; this process is called annihilation .
antipode
   (NASA Thesaurus / NASA SP-7, 1965)
Anything exactly opposite to something else. Particularly, that point on the earth 180° from a given place.
antiquities
   (NASA Thesaurus)
Man-made objects or surviving parts or fragments from the past.
antiradiation missiles
   (NASA Thesaurus)
Missiles that attack radiating targets such as radar transmitters, etc.
antireflection coatings
   (NASA Thesaurus)
Thin dielectric or metallic films applied to an optical surface to reduce the reflectance and thereby increase the transmittance. Note: The ideal value of the reactive index of a single layered film is the square root of the product of the refractive indices on either side of the film, the ideal optical thickness being one quarter of a wavelength.
antiresonance
   (NASA SP-7, 1965)
For a system in forced oscillation, the condition existing at a point when any change, however small, in the frequency of excitation causes an increase in the response at this point.
antisite defects
   (NASA Thesaurus)
Point defects occurring in crystalline compounds where an atom of one atomic species occupies an atomic site that is allocated to a different atomic species (e.g., in GaAs, an arsenic atom may sit on a site allocated to a gallium atom). If the nearest neighbor sites are occupied with the correct species for their sites (e.g., an arsenic antisite atom surrounded by arsenic atoms), the antisite atom is then bonded to four like atoms (rather than four Ga atoms). Such a configuration is not electrically neutral, but acts as a double donor. An "antisite pair" occurs if two adjacent atoms have simply been interchanged.
antisolar point
   (NASA SP-7, 1965)
The point on the celestial sphere 180° from the sun.
Antlia
   (NASA SP-7, 1965)
(abbr Ant, Antl.)
See constellation.
anvil clouds
   (Glossary of Weather Terms for Storm Spotters - NOAA)
The flat, spreading top of a cumulonimbus, often shaped like an anvil. Thunderstorm anvils may spread hundreds of miles downwind from the thunderstorm itself, and sometimes may spread upwind.
anxiety
   (NASA Thesaurus)
Nervous or fear reaction to a perception of danger.
AO
   (Space Flight Glossary - JPL)
Announcement of Opportunity.
AOS
   (Space Flight Glossary - JPL)
Acquisition Of Signal, used in DSN operations.
AOSO
   (AS&T Dictionary)
The Advanced Orbiting Solar Observatory (AOSO) was a project to develop a successor to the Orbiting Solar Observatory proposed in 1962 by the Space Science Board in 1965. The project was deemed too costly and was cancelled in December of that year. Some of the experiments it would have carried were executed during the Skylab project.
apareon
   (NASA SP-7, 1965)
The point on a Mars-centered orbit where a satellite is at its greatest distance from Mars. Apareon is analogous to apogee . See geo.
apastron
   (High Energy Astrophysics Dictionary- GSFC)
The point of greatest separation of two stars, as in a binary star orbit.
apastron
   (NASA SP-7, 1965)
That point of the orbit of one member of a binary star system at which the stars are farthest apart. That point at which they are closest together is called periastron .
aperiodic
   (NASA SP-7, 1965)
Without a period; not cyclic; completely damped.
aperture
   (Plasma Physics and Fusion Energy Glossary)
An opening in an optical system which restricts the size of the bundle of rays incident on a given surface. (Usually circular and specified by diameter.)
aperture
   (NASA SP-7, 1965)
1. An opening; particularly, that opening in the front of a camera through which light rays pass when a picture is taken.
2. The diameter of the objective of a telescope or other optical instrument, usually expressed in inches, but sometimes as the angle between lines from the principal focus to opposite ends of diameter of the objective.
3. Of a unidirectional antenna, that portion of a plane surface near the antenna, perpendicular to the direction of maximum radiation, through which the major part of the radiation passes. See effective area.
aperture ratio
   (NASA SP-7, 1965)
The ratio of the useful diameter of a lens to its focal length. It is the reciprocal of the f-number.
In application to an optical instrument, rather than to a lens, numerical aperture is more commonly used. The aperture ratio is then twice the tangent of the angle whose sine is the numerical aperture.
apex of the sun's motion
   (NASA SP-7, 1965)
= solar apex
apex of the sun's way
   (NASA SP-7, 1965)
= solar apex
APFO--Aerial Photography Field Office
   (Global Land Information System Glossary - USGS)
The U.S. Department of Agriculture's APFO is managed by the Farm Service Agency (FSA). FSA was formerly known as the Agricultural Stabilization and Conservation Service (ASCS). APFO is the repository for all of the USDA's aerial photography. The archive contains over 50,000 rolls of film acquired over the last 40 years and includes over 14 million frames of coverage of the conterminous U.S., Alaska, and Hawaii. APFO provides photographic products to local county, State and Federal offices within the U.S. Department of Agriculture (USDA) including FSA, National Resources Conservation Service (NRCS), and the Forest Service. They also serve the general public with similar products upon request at the cost of reproduction.
aphelion
   (AS&T Dictionary)
The point on the orbit of a planet, comet, or celestial body at which it is farthest from the sun.
aphelion
   (NASA SP-7, 1965)
That point in a solar orbit which is most distant from the sun. The point nearest the sun is called perihelion.
APL (programming language)
   (NASA Thesaurus)
"A Programming Language" is a high level interactive computer language primarily designed for mathematical applications. It was developed by Kenneth Iverson in 1962. It is characterized by extensive operators and array handling capability. NASA Goddard was one of the first users and was instrumental in introducing APL to the computer community.
apoapsis
   (Imagine the Universe Dictionary - NASA GSFC)
The point in an orbit when the two objects are farthest apart. Special names are given to this orbital point for commonly used systems. For example, the point of greatest separation of two stars, as in a binary star orbit, is called apastron; the point in its orbit where a planet is farthest from the Sun is called aphelion; the point in its orbit where an Earth satellite is farthest from the Earth is called apogee.
apoapsis
   (Space Flight Glossary - JPL)
The farthest point in an orbit from the body being orbited.
apoapsis
   (NASA SP-7, 1965)
That point in an orbit farthest from the center of attraction.
apocenter
   (NASA SP-7, 1965)
= apofocus
apocynthion
   (NASA SP-7, 1965)
That point in the orbit of a moon satellite which is farthest from the moon.
apofocus
   (NASA SP-7, 1965)
The point on an elliptic orbit at the greatest distance from the principal focus.
apogee
   (NASA SP-7, 1965)
1. That point in a geocentric orbit which is most distant from the earth. That orbital point nearest the earth is called perigee . See geo.
By extension, apogee and perigee are also used in reference to orbits about other planets and natural satellites.
2. Of a satellite or rocket: To reach its apogee (sense 1), as in the Vanguard apogees at 2,560 miles .
apogees
   (NASA Thesaurus)
Those orbital points farthest from the Earth, when the Earth is the center of attraction.
apojove
   (Space Flight Glossary - JPL)
Apoapsis in Jupiter orbit.
Apollo 10 flight
   (AS&T Dictionary)
A United States manned space flight mission launched on a Saturn V rocket by the National Aeronautics and Space Administration May 18, 1969 which returned to Earth May 26, 1969. Highlights included the first manned Command Service Module/Lunar Module operations in cislunar and lunar environment and the simulation of the first lunar landing profile.
Apollo 11 flight
   (AS&T Dictionary)
A United States manned space flight mission launched on a Saturn V rocket by the National Aeronautics and Space Administration July 16, 1969 which returned to Earth July 24, 1969. Highlights included the first man to step on the lunar surface, and the first liftoff of a spacecraft from the lunar surface.
Apollo 12 flight
   (AS&T Dictionary)
A United States manned space flight mission launched on a Saturn V rocket by the National Aeronautics and Space Administration November 14, 1969 which returned to Earth November 24, 1969. Highlights included the retrieval of parts of the unmanned Surveyor 3, which had landed on the lunar surface in April 1967, and the deployment of the Apollo Lunar Surface Experiments Package (ALSEP). In addition 34kg of lunar soil and rock samples were collected and were returned to earth for study.
Apollo 13 flight
   (AS&T Dictionary)
A United States manned space flight mission launched on a Saturn V rocket by the National Aeronautics and Space Administration April 11, 1970 which returned to Earth April 17, 1970. An explosion in an oxygen tank on April 13th caused sufficient damange to require an emergency return to earth and discontinuation of the mission.
Apollo 14 flight
   (AS&T Dictionary)
A United States manned space flight mission launched on a Saturn V rocket by the National Aeronautics and Space Administration January 31, 1971 which returned to Earth February 9, 1971. The lunar module landed in the lunar region called Fra Mauro where the Apollo Lunar Surface Experiments Package (ALSEP) was deployed. 42 kg of lunar material was collected and returned to Earth for study.
Apollo 15 flight
   (AS&T Dictionary)
A United States manned space flight mission launched on a Saturn V rocket by the National Aeronautics and Space Administration July 26, 1971 which returned to Earth August 7, 1971. The lunar module landed in the lunar region calledHadley-Apennine region where the Lunar Roving Vehicle (LRV) was first used. A small sub-satellite was left in lunar orbit for first time and 6.6 kg of material were gathered for return to earth for study.
Apollo 16 flight
   (AS&T Dictionary)
A United States manned space flight mission launched on a Saturn V rocket by the National Aeronautics and Space Administration April 16, 1972 which returned to Earth April 27, 1972. The lunar module landed in the lunar region called the Descartes Highlands where selected surface experiments were deployed, an ultraviolet camera/spectrograph was used for first time on the Moon. 95.8 kg of material were gathered for return to earth for study.
Apollo 17 flight
   (AS&T Dictionary)
A United States manned space flight mission launched on a Saturn V rocket by the National Aeronautics and Space Administration December 7, 1972 which returned to Earth December 19, 1972. The lunar module landed in the lunar region called the Taurus-Littrow Highlands and Valley where geological surveying and sampling of materials and surface features were performed, and surface experiments deployed and activated. In the command module, inflight experiments were conducted and photographic tasks were performed during lunar orbit and transearth coast (TEC). 110.4 kg of material were gathered for return to earth for study. It was the first time a scientist served as an astronaut.
Apollo 5 flight
   (AS&T Dictionary)
A United States unmanned space flight mission launched on a Saturn 1B rocket by the National Aeronautics and Space Administration January 22, 1968. Its mission objectives were to verify operation of the lunar module ascent and descent propulsion systems, to evaluate lunar module staging, and to evaluate S-IVB instrument unit performance.
Apollo 6 flight
   (AS&T Dictionary)
A United States unmanned space flight mission launched on a Saturn V rocket by the National Aeronautics and Space Administration April 4, 1968. Its mission objectives were to demonstrate structure and thermal integrity and compatibility of the launch vehicle and the spacecraft, to confirm launch loads and dynamic characteristics, to demonstrate the separation of launch vehicle stages, to evaluate performance of emergency detection system in closed-loop configuration, to verify the operation of Saturn V propulsion, guidance and control, and electrical systems, and to demonstrate performance of mission support facilities. All but the verification of the Saturn V performance were achieved.
Apollo 7 flight
   (AS&T Dictionary)
A United States manned space flight mission launched on a Saturn 1B rocket by the National Aeronautics and Space Administration October 11, 1968 which returned to Earth October 22, 1968. It demonstrated command service module (CSM)/crew performance and crew, space vehicle, and mission support facilities performance during a manned CSM mission, and demonstrated CSM rendezvous capability.
Apollo 8 flight
   (AS&T Dictionary)
A United States manned space flight mission launched on a Saturn V rocket by the National Aeronautics and Space Administration December 21, 1968 which returned to Earth December 27, 1968. It demonstrated crew, space vehicle, and mission support facilities during manned Saturn V/command service module (CSM) mission, translunar injection, CSM navigation, communications, and midcourse corrections, assessed CSM consumables and passive thermal control, demonstrated CSM performance in cislunar and lunar orbit environment, demonstrated communications and tracking at lunar distances and returned high-resolution photographs of proposed Apollo landing sites and locations of scientific interest.
Apollo 9 flight
   (AS&T Dictionary)
A United States manned space flight mission launched on a Saturn V rocket by the National Aeronautics and Space Administration March 03, 1969 which returned to Earth March 13, 1969. The mission demonstrated crew, space vehicle, and mission support facilities during manned Saturn V/ command service module (CSM)/ lunar module (LM) mission, LM/crew performance, selected lunar orbit rendezvous mission activities including transposition, docking withdrawal, intervehicular crew transfer, extravehicular activity (EVA), stage burns, and LM active rendezvous and docking, and assess CSM/LM consumables used. All were achieved except EVA because of astronaut illness. .
Apollo asteroids
   (NASA Thesaurus)
Earth grazing asteroids in orbits between Mars and Jupiter, and crossing the Earth's orbit. This group contains 19 known asteroids.
Apollo extension system
   (AS&T Dictionary)
Various additions to the Apollo project proposed to continue the use of technologies developed during flights prior Apollo 11, which completed the primary mission of placing a human on the lunar surface. Intended to extend the demonstrated usefulness of the program through moderate improvements in systems, it was the forerunner of the Apollo Applications Program.
Apollo flights
   (AS&T Dictionary)
United States space flight missions launched on Saturn rockets by the National Aeronautics and Space Administration from February 26, 1966 to December 7, 1972 with the objective of landing a man on the moon and returning him safely to earth, and of collecting scientific information from the lunar surface.
Apollo Lunar Surface Experiments Package
   (AS&T Dictionary)
One of any sets of detection and research instruments and experiments flown to the lunar surface by Apollo 12, 14, 15, 16, and 17, with different objectives and equipment being included for each flight.
Apollo project
   (AS&T Dictionary)
A group of space launch missions from 1966-1972 which included flights to the lunar surface for exploration, experimentation, and collecting of samples of lunar material. The first human to step onto the lunar surface was a highlight of this project.
Apollo short stack
   (AS&T Dictionary)
The portion of the Apollo rocket and spacecraft connective assembly which included the forward skirt, instrument unit, and spacecraft lunar module adapter.
Apollo Soyuz test project
   (AS&T Dictionary)
The first international manned spaceflight. It was designed to test the compatibility of rendezvous and docking systems for American and Soviet spacecraft, to open the way for international space rescue as well as future joint manned flights.
Apollo spacecraft
   (AS&T Dictionary)
Vehicles designed to be used in space, launched from Earth by a Saturn rocket during the Apollo Project from 1966-1972.
Apollo telescope mount
   (AS&T Dictionary)
An X-ray telescope primarily used for Solar observation. It was mounted on the Skylab Space Station.
apolune
   (Space Flight Glossary - JPL)
Apoapsis in lunar orbit.
apostilb
   (NASA SP-7, 1965)
A unit of luminance equal to one over pi times ten to the minus fourth international candles per square centimeter. Compare stilb.
apparent
   (NASA SP-7, 1965)
In astronomy, observed.
True values are reduced from apparent (observed) values by eliminating those factors such as refraction, light time, etc., which affected the observation.
apparent additional mass
   (NASA SP-7, 1965)
A fictitious mass of fluid added to the mass of the body to represent the force required to accelerate the body through the fluid.
The apparent additional mass has inertia and momentum equal to the apparent increase of the inertia and momentum of the body.
apparent force
   (NASA SP-7, 1965)
A force introduced in a relative coordinate system in order that Newton laws of motion be satisfied in this system. This force must be equal and opposite to an acceleration in an inertial coordinate system, in which Newton laws are (by definition) satisfied. Examples are the coriolis force, and the centrifugal force incorporated in gravity.
apparent gravity
   (NASA SP-7, 1965)
= acceleration of gravity.
apparent horizon
   (Spacetime Wrinkles Glossary)
A surface on which outgoing light rays are just trapped, and cannot expand outward. It is a stronger condition than the event horizon, and the apparent horizon always lies inside the event horizon, or coincides with it.
apparent motion
   (NASA SP-7, 1965)
Motion relative to a specified or implied reference point which may itself be in motion. Also called relative motion . See relative movement.
In astronomy apparent motion usually refers to movement of celestial bodies as observed from the earth.
apparent motion
   (From Stargazers to Starships Glossary - GSFC)
The observed motion of a heavenly body across the celestial sphere, assuming the Earth is at the sphere's center and is standing still.
apparent position
   (NASA SP-7, 1965)
The position on the celestial sphere at which a heavenly body (or a space vehicle) would be seen from the center of the earth at a particular time. Compare astrometric position.
The apparent position of a body is displaced from the true position at the time of observation by the motion of the body during the time it takes light to travel from the body to the earth (see planetary aberration) and by aberration.
Most ephemerides tabulate apparent position of the sun, moon, and planets.
apparent solar day
   (NASA SP-7, 1965)
The duration of one rotation of the earth on its axis, with respect to the apparent sun. It is measured by successive transits of the apparent sun over the lower branch of a meridian. The length of the apparent solar day is 24 hours of apparent time and averages the length of the mean solar day, but varies somewhat from day to day.
apparent solar time
   (NASA SP-7, 1965)
See solar time.
apparent stresses
   (NASA SP-7, 1965)
= Reynolds stresses.
apparent sun
   (NASA SP-7, 1965)
The actual sun as it appears in the sky. Also called true sun . See mean sun, dynamical mean sun.
apparent time
   (NASA SP-7, 1965)
Time based upon the rotation of the earth relative to the apparent or true sun. This is the time shown by a sundial. See equation of time.
Apparent time may be designated as either local or Greenwich, as the local or Greenwich meridian is used as the reference.
apparent wander
   (NASA SP-7, 1965)
Apparent change in the direction of the axis of rotation of a spinning body, as a gyro, due to rotation of the earth. Often shortened to wander . See precession.
The horizontal component of apparent wander is called drift, and the vertical component is called topple .
Appleton layer
   (NASA SP-7, 1965)
= F2-layer
See ionosphere.
applications programs (computers)
   (NASA Thesaurus)
Software designed to fulfill specific needs of a user; for example, software for navigation, payroll, or process control.
approach control
   (NASA Thesaurus)
The control process which delivers aircraft to the final approach course or landing system properly spaced for their landing.
approximate absolute temperature scale
   (NASA SP-7, 1965)
(abbr AA)
A temperature scale with the ice point at 273° and boiling point of water at 373°. It is intended to approximate the Kelvin temperature scale with sufficient accuracy for many sciences, notably meteorology, and is widely used in the meteorological literature. Also called tercentesimal thermometric scale .
appulse
   (NASA SP-7, 1965)
1. The near approach of one celestial body to another on the celestial sphere, as in occultation, conjunction, etc.
2. A penumbral eclipse of the moon.
apron
   (NASA SP-7, 1965)
Specifically, a protective device specially designed to cover an area surrounding the fuel inlet on a rocket or spacecraft.
Aps, Apus
   (NASA SP-7, 1965)
International Astronomical Union abbreviations for Apus . See constellation.
apse
   (NASA SP-7, 1965)
= apsis
apselene
   (Space Flight Glossary - JPL)
Apoapsis in lunar orbit.
apsides
   (NASA SP-7, 1965)
Plural of apsis.
apsis
   (NASA SP-7, 1965)
(plural apsides) In celestial mechanics, either of the two orbital points nearest or farthest from the center of attraction. Also called apse . The apsides are the perihelion and aphelion in the case of an orbit about the sun, and the perigee and apogee in the case of an orbit about the earth. The line connecting these two points is called line of apsides . The nearest point is the lower apsis while the farthest point if the higher apsis.
APU (abbr)
   (NASA SP-7, 1965)
= auxiliary power unit.
Aql, Aqil.
   (NASA SP-7, 1965)
International Astronomical Union abbreviations for Aquila . See constellation.
Aquarid meteoroids
   (AS&T Dictionary)
Any of several groups of small, spaceborne rocks which when viewed from Earth appear to radiate out of the constellation Aquarius.
Aquarius
   (NASA SP-7, 1965)
(abbr Aqr, Aqar).
aquatic plants
   (NASA Thesaurus)
Plants growing in or on water.
aqueous vapor
   (NASA SP-7, 1965)
= water vapor.
aquiclude
   (Glossary of Hydrologic Terms - NOAA)
A formation which contains water but cannot transmit it rapidly enough to furnish a significant supply to a well or spring.
aquiculture
   (NASA Thesaurus)
The cultivation (breeding, raising, and harvesting) of fish, mollusks, shellfish, and/or other aquatic life as sources of food.
aquifers
   (NASA Thesaurus)
Bodies of rock that contain sufficient saturated permeable material to conduct ground water and to yield economically significant quantities of ground water to wells and springs.
aquifuge
   (Glossary of Hydrologic Terms - NOAA)
A geologic formation which has no interconnected openings and cannot hold or transmit water.
Aquila
   (NASA SP-7, 1965)
(abbr Aqr, Aqar)
See constellation.
Ara
   (NASA SP-7, 1965)
(abbr Ara, Arae)
See constellation.
Arago point
   (NASA SP-7, 1965)
One of the three commonly detectable points along the vertical circle through the sun at which the degree of polarization of diffuse sky radiation goes to zero; a neutral point.
The Arago point, so named for its discoverer, is customarily located at about 20° above the antisolar point; but it lies at higher altitudes in turbid air. The latter property makes the Arago distance a useful measure of atmospheric turbidity.
aragonite
   (NASA Thesaurus)
A white, yellowish, or gray orthorhombic mineral, that contains calcium carbonate.
arc
   (NASA SP-7, 1965)
1. A part of a curved line, as a circle.
2. A luminous glow which appears when an electric current passes through ionized air or gas.
3. An auroral arc. See aurora. See arc discharge.
arc degree
   (Spacetime Wrinkles Glossary)
The size of a celestial object expressed in terms of the angle that it covers (or "subtends") when viewed from Earth. For example, the moon subtends an angle of 1/2 a degree. One degree of arc is defined as equivalent to 60 minutes of arc (or "arc minutes"). Arc minutes are further divided into arc seconds, such that there 60 x 60 or 3600 arc seconds per degree. So the moon's apparent size can also be expressed as 1/2 degree x 3600 = 1800 arc seconds. If the distance to an object is also known, then its angular size can be used to calculate its diameter in miles or kilometers.
arc discharge
   (NASA SP-7, 1965)
A luminous, gaseous, electrical discharge in which the charge transfer occurs continuously along a narrow channel of high ion density. An arc discharge requires a continuous source of electric potential difference across the terminals of the arc.
Arc discharge is to be distinguished from corona discharge, point discharge, and spark discharge.
arc spectrum
   (NASA SP-7, 1965)
The spectrum of a neutral atom, designated by the Roman numeral I following the symbol for the element, and He I. See spark spectrum.
ARC/INFO
   (Global Land Information System Glossary - USGS)
ARC/INFO is a geographic information system (GIS) used to automate, manipulate, analyze, and display geographic data in digital form. ARC/INFO is a proprietary system developed and distributed by the Environmental Systems Research Institute, Inc., in Redlands, California. DISCLAIMER: Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
arch dam
   (Glossary of Hydrologic Terms - NOAA)
A concrete arch dam is used in sites where the ratio of width between abutments to height is not great and where the foundation at the abutments is solid rock capable of resisting great forces. The arch provides resistance to movement. When combined with the weight of concrete (arch-gravity dam), both the weight and shape of the structure provide great resistance to the pressure of water.
archaebacteria
   (NASA Thesaurus)
Organisms belonging to the taxonomic kingdom of the same name which are characterized by distinct t- and r-RNAs, the absence of peptoglycan cell walls and their possible replacement by a proteinaceous coat, ether-linked lipids from phytanyl chains, and occurrence in unusually harsh habitats, e.g., methane, halide and thermoacidic environments. These hardy bacteria are significant in the study of the origin of life.
archipelagoes
   (NASA Thesaurus)
Seas or areas in seas that contain numerous islands; also the island groups themselves.
architecture (computers)
   (NASA Thesaurus)
The design of system and logic organization and information flow relationships in a computer rather than the circuit and component features.
arcs
   (Plasma Physics and Fusion Energy Glossary)
Types of electrical discharge between two electrodes; characterized by high current density. Similar in meaning to "spark" in common language. See also unipolar arcs.
arcs with ray structure
   (NASA SP-7, 1965)
See aurora.
arctic blackout
   (NASA SP-7, 1965)
= blackout.
ARDC model atmosphere
   (NASA SP-7, 1965)
See standard atmosphere.
area navigation
   (NASA Thesaurus)
A method of navigation that permits aircraft operation on any desired course within the coverage of station-referenced navigation signals or within the limits of self-contained system capability.
area of influence
   (Glossary of Hydrologic Terms - NOAA)
The area covered by the drawdown curves of a given pumping well or combination of wells at a particular time.
area rule
   (NASA SP-7, 1965)
A prescribed method of design for obtaining minimum zero-lift drag for a given aerodynamic configuration, such as a wing-body configuration, at a given speed.
For a transonic body, the area rule is applied by subtracting from, or adding to, its cross-sectional area distribution normal to the air stream at various stations so as to make its cross-sectional area distribution approach that of an ideal body of minimum drag; for a supersonic body, the sectional areas are frontal projections of areas intercepted by planes inclined at the Mach angle.
area-capacity curve
   (Glossary of Hydrologic Terms - NOAA)
A graph showing the relation between the surface area of the water in a reservoir, the corresponding volume, and elevation.
areal
   (Global Land Information System Glossary - USGS)
Relating to or involving an area.
areal radiant intensity
   (AS&T Dictionary)
See radiance.
areal velocity
   (NASA SP-7, 1965)
In celestial mechanics, the area swept out by the radius vector per unit time.
The areal velocity is constant for a central force. See Kepler laws.
Arend-Roland comet
   (AS&T Dictionary)
A comet discovered by Sylvain Arend and Georges Roland of the Royal Observatory of Belgium on November 8, 1956.
areo
   (NASA SP-7, 1965)
Combining form of Mars (Ares), as in areography.
Words formed with aero are considered pedantic by some. See geo.
areographic
   (NASA SP-7, 1965)
Referring to positions on Mars measured in latitude from Mars' equator and in longitude from a reference meridian.
areography
   (NASA SP-7, 1965)
The study of the surface features of Mars; the geography of Mars.
Ares
   (NASA SP-7, 1965)
Mars.
Ares is seldom used except in combining forms as areocentric, apareon.
Arg
   (NASA SP-7, 1965)
International Astronomical Union abbreviation for Argo . See constellation.
Argo
   (NASA SP-7, 1965)
(abbr Arg).
argument
   (NASA SP-7, 1965)
In astronomy, an angle or arc, as in argument of perigee .
argument of latitude
   (NASA SP-7, 1965)
In celestial mechanics, the angular distance measured in the orbit plane from the ascending node to the orbiting object; the sum of the argument of perigee and the true anomaly.
argument of periapsis
   (Space Flight Glossary - JPL)
The argument (angular distance) of periapsis from the ascending node.
argument of perigee
   (NASA SP-7, 1965)
In celestial mechanics, the angle or arc, as seen from a focus of an elliptical orbit, from the ascending node to the closest approach of the orbiting body to the focus. The angle is measured in the orbital plane in the direction of motion of the orbiting body.
Argus (project)
   (Earth's Magnetosphere Glossary - GSFC)
Argus (project)--A 1958 experiment by the US military, to create artificial radiation belts by exploding small nuclear bombs above the atmosphere.
Ari, Arie
   (NASA SP-7, 1965)
International Astronomical Union abbreviations for Aries. See constellation.
arid lands
   (Glossary of Hydrologic Terms - NOAA)
Regions where precipitation is so deficient in quantity, or occurs at such times, that agriculture is impracticable without irrigation.
Ariel
   (NASA Thesaurus / NASA SP-7, 1965)
A satellite of Uranus orbiting at a mean distance of 192,000 kilometers.
Ariel 5 satellite
   (NASA Thesaurus)
One in a series of artificial satellites launched for Britain by the United States.
Aries
   (NASA SP-7, 1965)
(abbr Ari, Arie)
See constellation.
Aries constellation
   (AS&T Dictionary)
A small group of stars visible from Earth in the Northern Hemisphere during the late winter and early spring. It lies on the ecliptic at right ascension 2.6600 hours, declination: 20.0900 degrees.
Aries sounding rocket
   (NASA Thesaurus)
The largest in terms of weight and volume of the sounding rockets. It has a 44 inch payload capacity.
Arietid meteoroids
   (AS&T Dictionary)
Any of several groups of small, spaceborne rocks which when viewed from Earth appear to radiate out of the constellation Aries.
arithmetic element
   (NASA SP-7, 1965)
= arithmetic unit.
arithmetic mean
   (NASA SP-7, 1965)
One of several accepted measures of central tendency, physically analogous to center of gravity. Pertaining to a set of numbers x 1, x2,...xn, the arithmetic mean, usually denoted by the symbol x bar , is the sum x1+x2+...+xn divided by n. Also called mean, average, simple average .
Since the word mean is also applied to other measures of central tendency, such as weighted means, geometric means, harmonic means, the adjective arithmetic is used for clarity. However, when used without further qualification, the term mean is understood as arithmetic mean.
arithmetic unit
   (NASA SP-7, 1965)
That part of a computer which performs arithmetic operations. Also called arithmetic element .
ARPA computer network
   (NASA Thesaurus)
The "Advanced Research Projects Agency" of the Department of Defense nationwide computer network incorporating digital communication between large numbers of dissimilar computers as well as direct access to programs, data, storage, etc. shared by all terminals.
array
   (NASA SP-7, 1965)
= antenna array.
arrhythmia
   (NASA Thesaurus / NASA SP-7, 1965)
Absence of rhythm, as, for example, in heart beat.
arrow wing
   (NASA SP-7, 1965)
An aircraft wing of V-shaped planform, either tapering or of constant chord, suggesting a stylized arrowhead.
arrow wings
   (NASA Thesaurus)
Aircraft wings of V-shaped planform, either tapering or of constant chord, suggesting a stylized arrowhead.
arroyos
   (Glossary of Hydrologic Terms - NOAA)
Water-carved channels or gullys in arid lands , usually rather small with steep banks, dry most of the time, because of infrequent rainfall and the shallowness of the cut which does not penetrate below the level of permanent groundwater.
artesian well
   (Glossary of Hydrologic Terms - NOAA)
A well drilled into confined groundwater with enough hydraulic pressure for the water to flow to the surface without pumping. Also called a flowing well.
artificial antenna
   (NASA SP-7, 1965)
A device which has the equivalent impedance characteristics of an antenna and the necessary power-handling capabilities, but which does not radiate nor intercept radiofrequency energy. Also called dummy antenna .
artificial asteroid
   (NASA SP-7, 1965)
A manmade object placed in orbit about the sun. See asteroid.
artificial earth satellite
   (NASA SP-7, 1965)
A manmade earth satellite, as distinguished from the moon.
artificial feel
   (NASA SP-7, 1965)
A control feel simulated by mechanisms incorporated in the control system of an aircraft or spacecraft where the forces acting on the control surfaces are not transmitted to the cockpit controls, as in the case of an irreversible control system or a power boosted system.
artificial gravity
   (NASA Thesaurus / NASA SP-7, 1965)
A simulated gravity established within a space vehicle by rotation or acceleration.
artificial horizon
   (NASA SP-7, 1965)
1. A gyro-operated flight instrument that shows the pitching and banking attitudes of an aircraft or spacecraft with respect to a reference line horizon, within limited degrees of movement, by means of the relative position of lines or marks on the face of the instrument representing the aircraft and the horizon. See attitude gyro.
2. A device, such as a spirit level, pendulum, etc., that establishes a horizontal reference in a navigation instrument.
artificial intelligence
   (NASA Thesaurus)
A discipline concerned with the development of computer and extended-robotic systems that can exhibit intelligent action. May also be defined as a subfield of computer science concerned with concepts and methods of symbolic inference by a computer and the symbolic representation of the knowledge to be used in making inferences.
artificial satellite
   (NASA Thesaurus / NASA SP-7, 1965)
A man-made satellite.
ASCA
   (Imagine the Universe Dictionary - NASA GSFC)
The Advanced Satellite for Cosmology and Astrophysics a Japanese Asuka spacecraft (formerly Astro-D)
ascendent
   (NASA SP-7, 1965)
The negative of the gradient. The ascendent of a function is a vector with magnitude equal to the maximum spatial rate of change of that function at a given point at a given time. It is directed toward increasing values of the function along the line of maximum change, and is represented by nabla del F, where F is the function and delta or nabla del (downward pointing triangle) the del-operator.
ascending node
   (NASA SP-7, 1965)
That point at which a planet, planetoid, or comet crosses to the north side of the ecliptic; that point at which a satellite crosses to the north side of the equatorial plane of its primary. Also called northbound node . The opposite is descending node or southbound node .
ascending node
   (Global Land Information System Glossary - USGS)
Direction satellite is traveling relative to the Equator. An ascending node would imply a northbound Equatorial crossing.
ASCII--American Standard Code for Information Interchange
   (Global Land Information System Glossary - USGS)
A seven-bit code standard adopted to facilitate data interchange between computers and operating systems. These codes represent alphanumerics and special characters (for example, $, /, ?, !).
asdic
   (NASA SP-7, 1965)
British term for sonar .
ashes
   (Plasma Physics and Fusion Energy Glossary)
Fusion reaction products trapped in a plasma. Ash is bad because (a) it generally radiates more strongly than the fuel ions, and thus reduces energy confinement, and (b) it creates additional plasma pressure and/or reduces pressure available for fuel ions. (due to beta limits, see beta)
Askania
   (NASA SP-7, 1965)
(a trade name) = cine-theodolite.
aspect ratio
   (Plasma Physics and Fusion Energy Glossary)
In toroidal geometry, the ratio of the major diameter (total width of the torus) to the minor diameter (width of a slice taken through one side of the ring).
aspect ratio
   (NASA Thesaurus / NASA SP-7, 1965)
The ratio of the square of the span of an airfoil to the total airfoil area, or the ratio of its span to its mean chord.
An airfoil of high aspect ratio is of relatively long span and short chord; one of low aspect ratio is of relatively short span and long chord.
aspects
   (NASA SP-7, 1965)
The apparent positions of celestrial bodies relative to one another; particularly, the apparent positions of the moon or a planet relative to the sun.
asphalt
   (NASA Thesaurus)
A dark brown to black cementitious material, in which the predominating constituents are bitumens which occur in nature or are obtained in petroleum processing.
asphaltenes
   (NASA Thesaurus)
Components of bitumens that are soluble in carbon disulphide but not in paraffin naphtha, constitute the solid dispersed particles of the bitumens, and consist of high molecular weight hydrocarbons.
aspheric optics
   (NASA Thesaurus)
Lenses whose surfaces are custom tuned to specific applications, thereby correcting aberrations in an optical system.
aspiration condenser
   (NASA SP-7, 1965)
An ion counter collecting element consisting of a cylindrical condenser which when charged produces a radial field which collects ions from the aspirated air.
assemble
   (NASA SP-7, 1965)
In computer terminology, to organize the subroutines into a complete program.
assisted take-off
   (NASA SP-7, 1965)
A take-off of an aircraft using a supplementary source of power, usually rockets. See RATO.
associated corpuscular emission
   (NASA SP-7, 1965)
The full complement of secondary charged particles (usually limited to electrons) associated with an X-ray or gamma ray beam in its passage through matter.
The full complement of electrons is obtained after the radiation has traversed sufficient matter to bring about equilibrium between the primary photons and secondary electrons. Electronic equilibrium with the secondary photons is intentionally excluded.
association reactions
   (NASA Thesaurus)
Gas phase chemical processes in which two molecular species A and B react to form a larger molecule AB. In astrophysics these processes are involved in the "condensation" of small gaseous molecules into larger species.
associative memory
   (NASA Thesaurus)
A method or device for data storage in which data is identified by a part or properties of its content, rather than by an address or relative position.
associative processing (computers)
   (NASA Thesaurus)
Byte-variable computer processing with multifield search, arithmetic, and logic capability.
assumed latitude
   (NASA SP-7, 1965)
See latitude.
assumed longitude
   (NASA SP-7, 1965)
See longitude.
Assured Crew Return Vehicle
   (NASA Thesaurus)
An aerospace vehicle designed to return space station crews to Earth quickly (less than 24 hours) in the event of crew illness/injury, space station catastrophe/failure, or transportation element catastrophe/failure.
asteroid
   (NASA Thesaurus / NASA SP-7, 1965)
One of the many small celestial bodies revolving around the sun, most of the orbits being between those of Mars and Jupiter. Also called planetoid, minor planet . See planet.
The term minor planet is preferred by many astronomers but asteroid continues to be used in astronomical literature, especially attributively, as in asteroid belt.
All asteroids with determined orbits (except for a few discovered during World War II) are numbered for identification in the order of their discovery. The Ephemerides of the Minor Planets published by the U.S.S.R. Academy of Sciences lists all numbered asteroids, data concerning them, and their predicted positions. The daily positions of the first four minor planets are tabulated in the American Ephemeris and Nautical Almanac. Orbits have been determined for approximately 1700 asteroids. Asteroids have names as well as numbers, see Table I. The names are usually feminine but masculine names have been used for asteroids closer to or farther away from the Sun than the majority. The first asteroid to be given a masculine name, Eros (number 443) was the first to be discovered inside the orbit of Mars. The Trojan asteroids, named for heroes of the Trojan war, are in the orbit of Jupiter.
asteroid belts
   (NASA Thesaurus)
The location of the orbits of most of the minor planets (estimated at a half million asteroids) between Mars and Jupiter; about 2000 asteroids have been assigned numbers and names.
asteroid capture
   (NASA Thesaurus)
The transfer of an asteriod or comet from the influence of a planet into that of another planet or neutral satellite.
asteroid missions
   (NASA Thesaurus)
Space missions for the study of asteroids and related celestial bodies.
asthenosphere
   (NASA Thesaurus)
Layer or shell of the Earth below the lithosphere which is weak and in which isostatic adjustments take place, magmas may be generated, and seismic waves are strongly attenuated.
astigmatism
   (NASA Thesaurus)
A defect of an optical system in consequence of which rays from a point fail to meet in a focal point resulting in a blurred and imperfect image.
astral dome
   (NASA SP-7, 1965)
= astrodome.
astre fictif
   (NASA SP-7, 1965)
A point on the celestial sphere used as a reference in measuring time intervals. See day.
astrionics
   (NASA Thesaurus)
Astronautical electronics, particularly the development and use of electronic equipment and systems for space vehicles and platforms.
astro
   (NASA SP-7, 1965)
A prefix meaning star or stars and, by extension, sometimes used as the equivalent of celestial , as in astro nautics.
astroballistics
   (NASA SP-7, 1965)
The study of the phenomena arising out of the motion of a solid through a gas at speeds high enough to cause ablation; for example, the interaction of a meteoroid with the atmosphere.
Astroballistics uses the data and methods of astronomy, aerodynamics, ballistics, and physical chemistry.
astrobiology
   (NASA SP-7, 1965)
The study of living organisms on celestial bodies other than the earth.
astrochemistry
   (High Energy Astrophysics Dictionary- GSFC)
The study of the chemical interactions between the gases and dust interspersed between the stars.
astrocompass
   (NASA SP-7, 1965)
An instrument used to determine direction by sighting heavenly bodies of known position.
astrodome
   (NASA SP-7, 1965)
A transparent dome in the fuselage or body of an aircraft or spacecraft intended primarily to permit taking celestial observations in navigating. Also called a navigation dome, astral dome .
astrodynamics
   (NASA Thesaurus / NASA SP-7, 1965)
The practical application of celestial mechanics, astroballistics, propulsion theory, and allied fields to the problem of planning and directing the trajectories of space vehicles.
Astrodynamics is sometimes used as a synonym for celestial mechanics. This usage should be discouraged.
astrogation
   (NASA SP-7, 1965)
Contraction of astronavigation .
astrographic position
   (NASA SP-7, 1965)
= astrometric position.
astrolabe
   (NASA Thesaurus / NASA SP-7, 1965)
1. In general, any instrument designed to measure the altitudes of celestial bodies.
2. Specifically, an instrument designed for very accurate celestial altitude measurements, as in survey work.
astrometric position
   (NASA SP-7, 1965)
The position of a heavenly body (or space vehicle) on the celestial sphere corrected for aberration but not for planetary aberration. Compare apparent position.
Astrometric positions are used in photographic observations where the position of the observed body can be measured in reference to the positions of comparison stars in the field of the photograph.
astrometry
   (Solar System Dynamics Glossary - JPL)
Astrometry pertains to the measurement of the position in the sky of solar-system bodies. Position measurements are typically made in right ascension and declination.
astrometry
   (NASA SP-7, 1965)
The branch of astronomy dealing with geometrical relations of the celestial bodies and their real and apparent motions. The techniques of astrometry, especially the determination of accurate position by photographic means, are used in tracking satellite and space probes.
astron machine
   (NASA SP-7, 1965)
An experimental thermonuclear device where a magnetic filed is generated by a relativistic ring of electrons and shaped into a magnetic mirror configuration. The hot electrons serve as a heat source to heat the ions.
astronaut
   (NASA SP-7, 1965)
1. A person who rides in a space vehicle.
2. Specifically, one of the test pilots selected to participate in Project Mercury, Project Gemini, Project Apollo, or any other United States program for manned space flight.
astronautic centrifuge
   (NASA SP-7, 1965)
See centrifuge.
astronautics
   (NASA SP-7, 1965)
1. The art, skill, or activity of operating spacecraft.
2. In a broader sense the science of space flight.
astronautics
   (NASA Thesaurus)
The science of space flight including the design, construction, and operation of spacecraft.
astronauts
   (AS&T Dictionary)
In the U.S., a person that is trained for or engages in flight in space.
astronavigation
   (NASA SP-7, 1965)
The plotting and directing of the movement of a spacecraft from within the craft by means of observations on celestial bodies. Sometimes contracted to astrogation or called celestial navigation .
astronomic
   (NASA SP-7, 1965)
= astronomical.
In any combination, such as astronomic coordinates, astronomic is equivalent to astromonical.
astronomic
   (Global Land Information System Glossary - USGS)
Pertaining to the science of astronomy. Astronomy is the science of the heavenly bodies (fixed stars, planets, satellites, and comets) their nature, distribution, magnitudes, motions, distances, periods of revolution, eclipses, etc
astronomical
   (NASA SP-7, 1965)
Of or pertaining to astronomy or to observations of the celestial bodies. Also called astronomic .
Astronomers have long preferred astronomical. Geodesists usually use astronomic as an intended parallel to geodetic. The Coast and Geodetic Survey uses astronomic in their publications insofar as is compatible with established practice.
astronomical constants
   (NASA SP-7, 1965)
1. The elements of the orbits of the bodies of the solar system, their masses relative to the sun, their size, shape, orientation, rotation, and inner constitution, and the velocity of light.
2. = system of astronomical constants.
The astronomical constants used in the calculations of The American Ephemeris and Nautical Almanac, as well as other national ephemerides, were adopted at various times between 1896 and 1930. Although the system was known to contain many inconsistencies, the International Astronomical Union recommended their continued use in 1952. Space-related research has provided data for the computation of a more accurate system, and in January 1964 The Working Group on the System of Astronomical Constants recommended a new system of constants to be introduced into the national and international ephemerides at the earliest practicable date. Both the conventional and revised systems are given in Table II. The constants in Table III were recommended for use in trajectory calculations for NASA programs by the Ad Hoc NASA Standards Constants Committee May 16, 1963.
astronomical coordinates
   (NASA Thesaurus / NASA SP-7, 1965)
Coordinates defining a point on the surface of the earth, or of the geoid, in which the local direction of gravity is used as a reference. Sometimes called geographic coordinates. See astronomical equator, astronomical latitude, astronomical longitude.
astronomical day
   (NASA SP-7, 1965)
A mean solar day beginning at mean noon, 12 hours later than the beginning of the civil day of the same date. Astronomers now generally use the civil day. See Julian day, astronomical time.
astronomical equator
   (NASA SP-7, 1965)
A line on the surface of the earth connecting points having 0° astronomical latitude. Sometimes called terrestrial equator.
When the astronomical equator is corrected for station error, it becomes the geodetic equator.
astronomical latitude
   (NASA SP-7, 1965)
Angular distance between the direction of gravity and the plane of the celestial equator. Sometimes called geographic latitude .
Astronomical latitude corrected for the meridional component of station error becomes geodetic latitude .
astronomical longitude
   (NASA SP-7, 1965)
The angle between the plane of the reference meridian and the plane of the celestial meridian. Sometimes called geographic longitude .
Astronomical longitude corrected for the prime-vertical component of station error divided by the cosine of the latitude becomes geodetic longitude .
astronomical meridian
   (NASA SP-7, 1965)
A line connecting points having the same astronomical longitude. Also called terrestrial meridian .
Because the deflection of the vertical varies from point to point, the astronomical meridian is an irregular line. When the astronomical meridian is corrected for station error, it becomes the geodetic meridian.
astronomical parallel
   (NASA SP-7, 1965)
A line connecting points having the same astronomical latitude.
Because the deflection of the vertical caries from point to point, the astronomical parallel is an irregular line. When the astronomical parallel is corrected for station error, it becomes the geodetic parallel.
astronomical polarimetry
   (NASA Thesaurus)
The measurement of electromagnetic radiation from celestial bodies by polarimeters.
astronomical position
   (NASA SP-7, 1965)
1. A point on the earth whose coordinates have been determined as a result of observation of celestial bodies.
The expression is usually used in connection with position on land determined with great accuracy for survey purposes.
2. A point on the earth, defined in terms of astronomical latitude and longitude.
astronomical refraction
   (NASA SP-7, 1965)
1. The angular difference between the apparent zenith distance of a celestial body and its true zenith distance, produced by refraction effects as the light from the body penetrates the atmosphere. Also called atmospheric refraction, astronomical refraction error. See Bemporad formula.
For bodies near zenith the astronomical refraction is only about 0.1 minute, but for bodies near the horizon it becomes about 30 minutes or more and contributes measurably to the length of the apparent day.
2. Any refraction phenomenon observed in the light originating from a source outside of the earth's atmosphere; as contrasted with terrestrial refraction. This is applied only to refraction caused by inhomogeneities of the atmosphere itself, and not to that caused by ice crystals suspended in the atmosphere.
astronomical refraction error
   (NASA SP-7, 1965)
= astronomical refraction, sense 1.
astronomical scintillation
   (NASA SP-7, 1965)
Any scintillation phenomena, such as irregular oscillatory motion, variation of intensity, and color fluctuation observed in the light emanating from am extraterrestrial source; to be distinguished from terrestrial scintillation primarily in that the light source for the latter lies somewhere within the earth's atmosphere. Also called stellar scintillation . See seeing.
Astronomical scintillation is typically strongest for celestial objects lying at large zenith distances and is not easily observed by eye for objects whose zenith distances are under 30°. Nonperiodic vibratory motions of stellar images with frequencies of the order of 1 to 10 cycles per second create a troublesome problem of seeing in astronomical work. The size of the schlieren producing vibratory scintillations has been estimated to be of the order of centimeters, and chromatic scintillations of celestial objects appear to be produced by parcels whose dimensions are of the order of decimeters or, perhaps, meters. Hence, astronomical scintillation is primarily a consequence of the high-frequency, short-wavelength type of atmospheric turbulence.
astronomical seeing
   (NASA SP-7, 1965)
See seeing.
astronomical solar time
   (NASA SP-7, 1965)
See solar time.
astronomical time
   (NASA SP-7, 1965)
Mean time reckoned from the upper branch of the meridian. See astronomical day.
astronomical triangle
   (NASA SP-7, 1965)
The navigational triangle, either terrestrial or celestial, used in the solution of celestial observations.
astronomical twilight
   (NASA SP-7, 1965)
See twilight.
astronomical unit
   (NASA SP-7, 1965)
(abbr AU)
1. A unit of length, usually defined as the distance from the earth to the sun, 149,599,000 kilometers.
This value for the AU was derived from radar observations of the distance of Venus. The value given in astronomical ephemerides, 149,500,000 kilometers, was derived from observations of the minor planet Eros.
2. The unit of distance in terms of which, in the Kepler Third Law,n2a3 = k2(1+m), the semimajor axis a of an elliptical orbit must be expressed in order that the numerical value of the Gaussian constant k may be exactly 0.01720209895 when the unit of time is the ephemeris day.
In astronomical units, the mean distance of the earth from the sun, calculated by the Kepler law from the observed mean motion n and adopted mass m, is 1.00000003.
astronomical unit (AU)
   (Imagine the Universe Dictionary - NASA GSFC)
149,597,870 km; the average distance from the Earth to the Sun.
astronomical unit (AU)
   (Comet Glossary - JPL)
Standard unit for measuring distance within the solar system. One AU is equal to the average distance between the Sun and Earth or about 93 million miles.
astronomical year
   (NASA SP-7, 1965)
= tropical year.
astronomy
   (NASA Thesaurus / NASA SP-7, 1965)
The science concerning the location, magnitudes, motions, and constitution of celestial bodies and structures.
astrophysics
   (NASA Thesaurus)
Study of the physical characteristics and processes associated with celestial bodies and interstellar space. The application of the laws of physics to the study of the celestial bodies and astronomical phenomena such as luminosity, size, mass, density, temperature, and chemical composition. Used for geoastrophysics.
astrophysics
   (NASA SP-7, 1965)
A branch of astronomy concerning the physical properties of celestial bodies, such as luminosity, size, mass, density, temperature, and chemical composition.
astrotracker
   (NASA SP-7, 1965)
= star tracker.
asymptotic properties
   (NASA Thesaurus)
Properties of any mathematical relation or corresponding physical system characterized by an approach to a given value as an expression, containing a variable, tends to infinity.
asynchronous computer
   (NASA SP-7, 1965)
An automatic computer in which succeeding operations are started by signals indicating the completion of the previous operation, rather than by signals from a master synchronizer. Contrast to synchronous computer. See variable cycle.
atelectasis
   (NASA Thesaurus / NASA SP-7, 1965)
Collapsed or airless state of all or part of a lung. Also called apneumatosis .
Aten asteroids
   (IMO Meteor Glossary)
Asteroids having semimajor axes a<1.0 au, and aphelion distances Q>0.983 au.
athodyd
   (NASA SP-7, 1965)
A type of jet engine consisting essentially of a duct or tube of varying diameter and open at both ends, which admits air at one end, compresses it by the forward motion of the engine, adds heat to it by the combustion of fuel, and discharges the resulting gases at the other end to produce thrust.
The ramjet is an athodyd; the pulsejet, especially the earlier type, is usually not considered an athodyd.
Atlas rocket
   (From Stargazers to Starships Glossary - GSFC)
An early liquid-fueled rocket, used by U.S. astronauts and still in use for unmanned launches. Because of its lightweight construction it uses no staging, but only drops two of its engines
atmosphere
   (NASA SP-7, 1965)
1. The envelope of air surrounding the earth; also the body of gases surrounding or comprising any planet or other celestial body. Compare biosphere, geosphere, hydrosphere, lithosphere. See atmospheric shell.
2. = standard atmosphere.
3. (abbr atm) A unit of pressure equal to 14.7 pounds per square inch.
atmospheres
   (NASA Thesaurus)
(1) The mixture of gases surrounding the Earth or filling the habitable volume of a spacecraft. (2) The pressure exerted by a column of mercury 760 mm high at 1G, equal to 101.329 kilopascals.
Atmospheric & Oceanographic Inform Sys
   (NASA Thesaurus)
A data system designed primarily for the interactive manipulation of meteorological satellite images. Capabilities include displaying, analyzing, storing, and manipulating digital data in the field of meteorology and Earth resources. Used for AOIPS.
atmospheric attenuation
   (AS&T Dictionary)
The depletion or reduction of luminance in a light beam or electromagnetic energy due to absorption, scattering or diffusion as it passes through the atmosphere.
atmospheric boil
   (NASA SP-7, 1965)
= terrestrial scintillation.
atmospheric boundary layer
   (NASA SP-7, 1965)
= planetary boundary layer.
atmospheric braking
   (NASA SP-7, 1965)

The action of slowing down an object entering the atmosphere of the earth or other planet from space, by using the drag exerted by air or other gas particles in the atmosphere; the action of the drag so exerted.
atmospheric chemistry
   (NASA Thesaurus)
Study of the production, transport, modification, and removal of atmospheric constituents in the troposphere and stratosphere.
atmospheric circulation
   (NASA Thesaurus)
Global or hemispheric air movements which can be treated by equations of motion in contrast to atmospheric diffusion which is small random movement not amenable to treatment by these equations. Used for wind circulation.
Atmospheric Cloud Physics Lab (Spacelab)
   (NASA Thesaurus)
A NASA Spacelab mission involving cloud physics experiments in zero gravity environment. Also known as ACPL. Used for ACPL (Spacelab) and zero-g ACPL (Spacelab).
atmospheric correction
   (NASA Thesaurus)
Removal of the effects of the intervening atmosphere from satellite imagery.
atmospheric duct
   (NASA SP-7, 1965)
An almost horizontal layer in the troposphere, extending from the level of a local minimum of the modified refractive index as a function of height, down to the level where the minimum value is again encountered, or down to earth's surface if the minimum value is not encountered again.
Atmospheric ducts may act as waveguides for radio and radar waves.
atmospheric electric field
   (NASA SP-7, 1965)
1. The electric-field strength of the atmosphere at any specified point in space and time.
2. The distribution of electrical potential in the atmosphere regarded merely from a geometric point of view as a typical scalar field (rarely used).
atmospheric electricity
   (NASA Thesaurus)
Electrical phenomena, regarded collectively, which occur in the Earth's atmosphere. Also the study of electrical processes occurring within the atmosphere.
atmospheric electricity
   (NASA SP-7, 1965)
1. Electrical phenomena, regarded collectively, which occur in the earth's atmosphere.
2. The study of electrical processes occurring within the atmosphere.
atmospheric entry
   (NASA Thesaurus / NASA SP-7, 1965)
The penetration of any planetary atmosphere by any object from outer space; specifically, the penetration of the earth's atmosphere by a manned or unmanned capsule or spacecraft.
Atmospheric General Circulation Experiment
   (NASA Thesaurus)
Model experiment of the Earth's atmospheric circulation as proposed for a Spacelab flight on which a liquid contained between two concentric spheres is subjected to rotation. The thermal driving force will be a stable radial temperature gradient and an unstable latitudinal gradient.
atmospheric interference
   (NASA SP-7, 1965)
= atmospherics.
atmospheric ion
   (NASA SP-7, 1965)
See ion.
atmospheric ionization
   (AS&T Dictionary)
The charging of neutral particles in the Earth's atmosphere through intense interaction with charged particles.
atmospheric lasers
   (NASA Thesaurus)
The theoretical phenomena whereby the upper atmosphere is used as the lasing medium.
atmospheric layer
   (NASA SP-7, 1965)
= atmospheric shell.
atmospheric noise
   (NASA SP-7, 1965)
= atmospherics.
atmospheric optics
   (NASA Thesaurus / NASA SP-7, 1965)
The study of the optical characteristics of the atmosphere and of the optical phenomena produced by the atmosphere's suspensoids and hydrometeors. It embraces the study of refraction, reflection, diffraction, scattering, and polarization of light, but is not commonly regarded as including the study of any other kinds of radiation. Also called meteorological optics.
atmospheric oscillation
   (NASA SP-7, 1965)
= atmospheric tide.
atmospheric physics
   (NASA SP-7, 1965)
= physical meteorology.
atmospheric physics
   (AS&T Dictionary)
A branch of science dealing with physical interactions of matter and energy in the Earth's atmosphere.
atmospheric pressure
   (NASA Thesaurus / NASA SP-7, 1965)
The pressure at any point in an atmosphere due solely to the weight of the atmospheric gases above the point concerned. See station pressure, sea-level pressure.
atmospheric radiation
   (NASA Thesaurus / NASA SP-7, 1965)
Infrared radiation emitted by or being propagated through the atmosphere. See insolation.
Atmospheric radiation, lying almost entirely within the wavelength interval of from 3 to 80 microns, provides one of the most important mechanisms by which the heat balance of the earth-atmosphere system is maintained. Infrared radiation emitted by the earth's surface (terrestrial radiation) is partially absorbed by the water vapor of the atmosphere which in turn remits it, partly upward, partly downward. This secondarily emitted radiation is then, in general, repeatedly absorbed and reemitted, as the radiant energy progresses through the atmosphere. The downward flux, or counterradiation, is of basic importance in the greenhouse effect; the upward flux is essential to the radiative balance of the planet.
atmospheric refraction
   (NASA Thesaurus / NASA SP-7, 1965)
Refraction resulting when a ray of radiant energy passes obliquely through an atmosphere.
It may be called "astronomical refraction" if the ray enters the atmosphere from outer space, or "terrestrial refraction" if it emanates from a point on or near the surface of the earth.
atmospheric region
   (NASA SP-7, 1965)
= atmospheric shell.
atmospheric scattering
   (AS&T Dictionary)
A diffusion or alteration in the direction of the propagation, frequency, or polarization of electromagnetic radiation through interaction with atoms in the Earth's atmosphere.
atmospheric scintillation
   (NASA SP-7, 1965)
= terrestrial scintillation.
atmospheric shell
   (NASA SP-7, 1965)
Any one of a number of strata or layers of the earth's atmosphere. Also called atmospheric layer, atmospheric region .
Temperature distribution is the most common criterion used for denoting the various shells. The troposphere (the region of change) is the lowest 10 or 20 kilometers of the atmosphere, characterized by decreasing temperature with height. The top of the troposphere is called the tropopause. Above the tropopause, the stratosphere, a region in which the temperature generally increases with altitude, extends to the , the top of the inversion layer, at about 50 to 55 kilometers. Above the stratosphere, the mesosphere, a region of generally decreasing temperatures with height extends to the mesopause, the base of an inversion layer at about 80 to 85 kilometers. The region above the mesopause, in which temperature generally increases with height, is the thermosphere.
The distribution of various physicochemical processes is another criterion. The ozonosphere, lying roughly between 10 and 50 kilometers, is the general region of the upper atmosphere in which there is an appreciable ozone concentration and in which ozone plays an important part in the radiative balance of the atmosphere; the ionosphere, starting at about 70 or 80 kilometers, is the region in which ionization of one or more of the atmospheric constituents is significant; the neutrosphere is the shell below this which is, by contrast, relatively unionized; and the chemosphere, with no very definite height limits, is the region in which photochemical reactions take place.
Dynamic and kinetic processes are a third criterion. The exosphere is the region at the top of the atmosphere, above the critical level of escape, in which atmospheric particles can move in free orbits, subject only to the earth's gravitation.
Composition is a fourth criterion. The homosphere is the shell in which there is so little photodissociation or gravitational separation that the mean molecular weight of the atmosphere is sensibly constant; the heterosphere is the region above this, where the atmospheric composition and mean molecular weight are not constant. The boundary between the two is probably at the level at which molecular oxygen begins to be dissociated, and this occurs in the vicinity of 80 or 90 kilometers.
The term mesosphere has been given another definition which does not fit into any logical set of criteria, i.e., the shell between the exosphere and the ionosphere. This use of mesosphere has not been widely accepted.
For further subdivisions, see ionosphere, troposphere, geocorona.
atmospheric shimmer
   (NASA SP-7, 1965)
= terrestrial scintillation.
atmospheric sounding
   (NASA Thesaurus)
Measurement of atmospheric phenomena generally with instruments carried aloft by spacecraft, rockets, etc.
atmospheric stratification
   (NASA Thesaurus)
The presence of strata or layers in the Earth's atmosphere. Used for atmospheric shells.
atmospheric tide
   (NASA Thesaurus / NASA SP-7, 1965)
Defined in analogy to the oceanic tide as an atmospheric motion on a worldwide scale, in which vertical accelerations are neglected (but compressibility is taken into account). Also called atmospheric oscillation .
Both the sun and moon produce atmospheric tides; and there exist both gravitational tides and thermal tides. The harmonic component of greatest amplitude, the 12-hour or semidiurnal solar atmospheric tide, is both gravitational and thermal in origin, the fact that it is greater than the corresponding lunar atmospheric tide being ascribed usually to a resonance in the atmosphere with a free period very close to the tidal period. Other tides of 6, 8, and 24 hours have been observed.
atmospheric transmissivity
   (NASA SP-7, 1965)
See transmission coefficient.
atmospheric windows
   (NASA Thesaurus)
Wavelength intervals at which the atmosphere transmits the most electromagnetic radiation.
atmospherics
   (NASA Thesaurus / NASA SP-7, 1965)
The radiofrequency electromagnetic radiation originating, principally, in the irregular surges of charge in thunderstorm lightning discharges. Atmospherics are heard as a quasi-steady background or crackling noise (static) in ordinary amplitude-modulated radio receivers. Also called atmospheric interference, strays, sferics . See sferics.
Since any acceleration of electric charge leads to emission of electromagnetic radiation, and since the several processes involved in propagation of lightning lead to very large charge accelerations, the lightning channel acts like a huge transmitter, sending out broad band radiation; the 10-kilocycle range propagates best and is used in detecting atmospherics. Atmospherics may occasionally be detected at distances in excess of 2000 miles from their source. Advantage has been taken of this in using radio direction-finding equipment to locate active thunderstorm areas in remote regions and in between weather reporting stations.
atolls
   (NASA Thesaurus)
Coral reefs appearing in plan view as roughly circular (though sometimes elliptical or horseshoe-shaped), and surmounted by a chain or ring of closely spaced low coral inlets that encircle a shallow lagoon in which there is no pre-existing land or islands of non-coral origin; the reefs are surrounded by deep water of the open sea, either oceanic or continental shelves. Atolls range in diameter from 1 km to more than 130 km, and are especially common today in the western and central Pacific Ocean. Atoll is derived from the native name in the Maldive Islands (Indian Ocean) which are typical examples of this structure.
atomic clock
   (NASA SP-7, 1965)
A timekeeping device controlled by the frequency of the natural vibrations of certain atoms.
atomic clocks
   (NASA Thesaurus)
Timekeeping devices controlled by the frequency of the natural vibrations of certain atoms.
atomic force microscopy
   (NASA Thesaurus)
A form of microscopy that allows the imaging of general surface morphology and surface atomic structure by the measurement of the atomic forces acting on a sharply pointed probe as it is moved across the surface of a specimen.
atomic gas
   (High Energy Astrophysics Dictionary- GSFC)
Gas that is composed of individual atoms (such as hydrogen or carbon) that are not bound to each other as molecules. Atomic gas may be ionized or mixed with molecular gas.
atomic mass
   (Plasma Physics and Fusion Energy Glossary)
Mass of an atom relative to 1/12th the mass of a carbon atom. Approximately equal to the sum of the number of protons and neutrons in the nucleus of the atom.
atomic mass
   (NASA SP-7, 1965)
The mass of a neutral atom of a nuclide usually expressed in atomic mass units. See atomic weight, mass number.
The atomic mass unit, amu, is exactly one-twelfth of the mass of a neutral atom of the most abundant isotope of carbon, C12=12.0000.
atomic mass unit
   (NASA SP-7, 1965)
(abbr amu)
See atomic mass, note.
atomic number
   (NASA SP-7, 1965)
(symbol Z)
An integer that expresses the positive charge of the nucleus in multiples of the electronic charge e. It is the number of electrons outside the nucleus of a neutral (un-ionized) atom and, according to widely accepted theory, the number of protons in the nucleus. See atomic weight, Table IV.
An element of atomic number Z occupies the Zth place in the periodic table of the elements. Its atom has a nucleus with a charge +Ze, which is normally surrounded by Z electrons, each of charge -e.
For example, the carbon isotope 6C14 has an atomic number of 6 and an atomic mass of 14.
atomic number (Z)
   (Plasma Physics and Fusion Energy Glossary)
The number of protons in a nucleus; sameas the number of electrons in a neutral atom; determines the position of an element in the periodic table, and hence its chemical properties (see also isotope).
atomic particle
   (NASA SP-7, 1965)
One of the particles of which an atom is constituted, as an electron, neutron, or a positively charged nuclear particle.
atomic rocket
   (NASA SP-7, 1965)
A projected rocket engine in which the energy for the jetstream is to be generated by atomic fission or fusion.
atomic temperature
   (Plasma Physics and Fusion Energy Glossary)
The temperature corresponding to the mean kinetic energy of the neutral atoms in a plasma.
atomic weight
   (NASA Thesaurus / NASA SP-7, 1965)
(abbr at. wt.)
The weight of an atom according to a scale of atomic weight units, awu, valued as one-twelfth the mass of the carbon atom (C12 = 12.00000). See Table IV.
Thus expressed, the atomic weight to the nearest integer is identical with the mass number.
atomic weight unit
   (NASA SP-7, 1965)
(abbr awu)
See atomic weight, note.
atomic-absorption spectrophotometry
   (Global Land Information System Glossary - USGS)
This destructive analytical technique is used to determine concentrations of specific chemical elements based on their emission or absorption of specific wavelengths of electromagnetic radiation.
atoms
   (Plasma Physics and Fusion Energy Glossary)
The smallest unit of an element that retains the characteristics of that element. At the center of the atom is the nucleus, made up of neutrons and protons, around which the electrons orbit.
attached shock
   (NASA SP-7, 1965)
= attached shock wave.
attached shock wave
   (NASA SP-7, 1965)
An oblique or conical shock wave that appears to be in contact with the leading edge of an airfoil or the nose of a body in a supersonic flow field. Also called attached shock.
attachment
   (NASA SP-7, 1965)
The process in which two particles collide and stick together forming a single complex particle. The most common attachment process is the formation of a negative ion from electron attachment to an atom or molecule. Some negative ions are unstable, however, and cannot survive.
The usual measure for this process is the attachment coefficient, which on the average is the fraction of a large number of collisions that result in attachment. Typical values of this fraction run from 1 in 10,000 to 1 in 1,000.
attachment coefficient
   (NASA SP-7, 1965)
See attachment, note.
attenuation
   (Glossary of Hydrologic Terms - NOAA)
The process where the flood crest is reduced as it progresses downstream.
attenuation
   (NASA Thesaurus / NASA SP-7, 1965)
Reduction in intensity.
attenuation coefficient
   (NASA Thesaurus / NASA SP-7, 1965)
(symbol alpha lower case)
A measure of the space rate of attenuation of any transmitted electromagnetic radiation. The attenuation coefficient is defined by

dI = -aI0dx
or
I = I0e-ax
where I is the flux density at the selected point in space; I0 is the flux density at the source; x is the distance from the source; and a is the attenuation coefficient.
In general, the attenuation coefficient is specified only when the attenuation is known to be due to both absorption and scattering, or when it is impossible to determine which is the cause. See absorption coefficient, scattering coefficient.
attenuation constant
   (NASA SP-7, 1965)
1. A measure of the rate of attenuation per unit length; the rate of flux-density (or power) reduction as energy (visual, electromagnetic, acoustic) propagates from its source. Also called attenuation factor, decay constant . Compare attenuation coefficient.
For free-space transmission of radar frequency energy, the attenuation constant is usually expressed in decibels per mile or kilometer (db/mi or db/km).
2. Specifically, of a traveling plane wave at a given frequency, the relative rate of decrease of amplitude of a field component (or of voltage or current) in direction of propagation in nepers per unit length.
attenuation factor
   (NASA SP-7, 1965)
= attenuation constant.
attenuation length
   (NASA SP-7, 1965)

The reciprocal of the attenuation coefficient.
attenuation ratio
   (NASA SP-7, 1965)
The magnitude of the propagation ratio.
attenuators
   (NASA Thesaurus)
Devices for measuring attenuation. They are usually calibrated in dB (decibels).
attitude
   (NASA Thesaurus / NASA SP-7, 1965)
The position or orientation of an aircraft, spacecraft, etc., either in motion or at rest, as determined by the relationship between its axes and some reference line or plane or some fixed system of reference axes.
attitude control
   (NASA Thesaurus / NASA SP-7, 1965)
1. The regulation of the attitude of an aircraft, spacecraft, etc.
2. A device or system that automatically regulates and corrects attitude, especially of a pilotless vehicle.
attitude gyro
   (NASA Thesaurus / NASA SP-7, 1965)
1. A gyro-operated flight instrument that indicates the attitude of an aircraft or spacecraft with respect to a reference coordinate system throughout 360° of rotation about each axis of the craft.
This instrument is similar to the artificial horizon, but has greater angular indication.
2. Broadly, any gyro-operated instrument that indicates attitude.
attitude jet
   (NASA SP-7, 1965)
A jetstream used to correct or alter the attitude of a flying body either in the atmosphere or in space; the nozzle that directs this jetstream.
The jet may be continuous or intermittent. A vernier engine is sometimes used to produce it.
attometer
   (Space Flight Glossary - JPL)
10-18 meter.
attribute
   (NASA SP-7, 1965)
A characteristic of a thing which can be appraised only in terms of whether it does or does not exist. See method of attributes.
attributes
   (Global Land Information System Glossary - USGS)
Attributes, also called feature codes or classification attributes, are used to describe map information represented by a node, line, or area. For example, an attribute code for an area might identify it to be a lake or swamp; an attribute code for a line might identify a road, railroad, stream, or shoreline.
attributes testing
   (NASA SP-7, 1965)
A reliability test procedure where the items under test are classified according to qualitative rather than quantitative characteristics.
AU
   (Solar System Dynamics Glossary - JPL)
AU is short for Astronomical Unit and defined as: the radius of a Keplerian circular orbit of a point-mass having an orbital period of 2*(pi)/k days (k is the Gaussian gravitational constant). One AU is slightly less than the average distance between the Earth and the Sun (approximately 1.5x10^11 m). See the table of astrodynamic constants for precise values.
AU (abbr)
   (NASA SP-7, 1965)
= astronomical unit.
audible sound
   (NASA SP-7, 1965)
Sound containing frequency components lying between about 15 and 20,000 cycles per second.
audio
   (NASA SP-7, 1965)
Pertaining to the audio frequency range.
The word audio may be used as a modifier to indicate a device or system intended to operate at audiofrequencies, e.g., audioamplifier.
audio data
   (NASA Thesaurus)
Useful information at audio signal frequency.
audio frequency
   (NASA Thesaurus / NASA SP-7, 1965)
Any frequency corresponding to a normally audible sound wave. See audio frequency range.
audio frequency range
   (NASA SP-7, 1965)
The range of frequencies to which the human ear is sensitive, approximately 15 cycles per second to 20,000 cycles per second. Also called audiorange.
audio signals
   (NASA Thesaurus)
Signals with a bandwidth of less than 20 kilohertz.
audiometry
   (NASA Thesaurus)
The testing and measurement of hearing at various levels.
audiorange
   (NASA SP-7, 1965)
= audio frequency range.
auditory sensation area
   (NASA Thesaurus / NASA SP-7, 1965)
In acoustics, the frequency region enclosed by the curves defining the threshold of pain and the threshold of audibility.
aufeis (ice)
   (NASA Thesaurus)
Icing of ground or river water in Arctic areas with continuous permafrost on which the water has continued to flow.
Auger effect
   (NASA Thesaurus)
The nonradiative transition of an atom from an excited electronic energy state to a lower state with the emission of an electron. The term usually refers to the x ray region of energy states. The final state corresponds to one higher degree of ionization than does the initial state. The effect is an alternative process to the transition to a lower state having the same degree of ionization with the emission of an x ray photon, and thus is analogous to the internal conversion of a nuclear transmission.
Auger shower
   (NASA SP-7, 1965)
A very large cosmic-ray shower. Also called extensive air shower .
augmentation
   (NASA SP-7, 1965)
The apparent increase in the semidiameter of a celestial body, as observed from the earth, as its altitude increases, due to reduced distance from the observer.
The term is used principally in reference to the moon.
augmentation correction
   (NASA SP-7, 1965)
A correction due to augmentation, particularly that sextant altitude correction due to the apparent increase in the semidiameter of a celestial body as its altitude increases.
augmenter tube
   (NASA SP-7, 1965)
A tube or pipe, usually one of several, through which the exhaust gases from an aircraft reciprocating engine are directed especially to provide additional thrust.
Aur, Auri
   (NASA SP-7, 1965)
International Astronomical Union abbreviations for Auriga . See constellation.
aural null
   (NASA SP-7, 1965)
See null.
Auriga
   (NASA SP-7, 1965)
(abbr Aur, Auri)
See constellation.
aurora
   (Earth's Magnetosphere Glossary - GSFC)
Aurora(short for polar aurora)--A glow in the sky, often observed in a ring-shaped region around the magnetic poles ("auroral zone") and occasionally further equatorward. The name comes from an older one, "aurora borealis," Latin for "northern dawn," given because an aurora near the northern horizon (its usual location when seen in most of Europe) looks like the glow of the sky preceding sunrise. Also known as "northern lights," although it occurs both north and south of the equator. The aurora is generally caused by fast electrons from space, guided earthward by magnetic field lines, and its light comes from collisions between such electrons and the atoms of the upper atmosphere, typically 100 km (60 miles) above ground.
aurora
   (NASA SP-7, 1965)
The sporadic radiant emission from the upper atmosphere over middle and high latitudes. It is believed to be due primarily to the emission from nitrogen - atomic N I and N II, molecular, N2, and ionic N2+; atomic oxygen (O I and O II); atomic sodium (Na I); the hydroxyl radical (OH); and hydrogen. Compare airglow.
According to various theories, auroras seem definitely to be related to magnetic storms and the influx of charged particles from the sun. The exact details of the nature of the mechanisms involved are still being investigated, but release of trapped particles from Van Allen belt apparently plays an important part. The aurora is most intense at times of magnetic storms (when it is also observed farthest equatorward), and shows a periodicity which is related to the sun's 27-day rotation period and the 11-year sunspot cycle. The distribution with height shows a pronounced maximum near 100 kilometers. The lower limit is probably near 80 kilometers.
The aurora can often be clearly seen, and it assumes a variety of shapes and colors which are characteristic patterns of auroral emission.
The following is the general classification and abbreviations of the forms of the auroras adopted by the International Union of Geodesy and Geophysics in 1930 for reporting of visual observations. The classification was modified slightly and expanded in 1963. The new classification is described in the
International Auroral Atlas , Aldine Pub. Co., Chicago, 1963.


I. Forms without ray structure:
HA (abbr for homogeneous quiet area). These can appear near the horizon, and between the arc and the horizon a dark segment is often seen. These arcs can be narrow or broad, and are very often diffuse along the upper border but sharp along the lower one.
HB (abbr for homogeneous bands). These forms do not have the regular shape of the arcs; they are more rapidly moving phenomena. The lower border is often irregular and sharp. The breadth can vary from a very narrow band to a band which is so large that it resembles a curtain hanging down. These bands very often turn into bands with ray structure.
PA (abbr for pulsating arcs). Parts of an arc flash up and disappear regularly within a period of about 20 seconds. This form quite often stands isolated in the sky without other auroras.
DS (abbr for diffuse luminous surfaces). These either appear like a diffuse veil or glow over great parts of the heavens without distinct boundaries, often appearing after intense displays of rays and curtains, or as more isolated feeble luminous streaks which sometimes bear a striking resemblance to clouds. Sometimes large areas of the heavens can be discolored by a green, violet, or red diffuse light.
PS (abbr for pulsating surfaces). Diffuse patches appear and disappear rhythmically at the same place, retaining the same irregular shape. When the patches are lying near the magnetic zenith the contours can be more sharp, and form a sort of corona. These forms appear often in connection with flaming auroras.
G (abbr for feeble glow near the horizon resembling the dawn). Of white or redlike color, this form is often the upper part of an arc whose lower border is below the horizon.

.

II. Forms with ray structure: These forms consist of short or long rays which can be arranged in different ways.
RA (abbr for arcs with ray structure). A homogeneous arc which has remained quiet and unaltered for a rather long time may become sharp and luminous along the lower border and they very rapidly change into an arc of rays. The rays can be short or long.
RBI (abbr for bands with ray structure). These resemble the bands mentioned under HB but are constituted of a series of rays which are arranged close to each other along the band, or they can appear more scattered. Often a series of parallel bands appear. When a band is near the magnetic zenith is may have the form of a corona.
D (abbr for draperies). If the ray become very long the band appears like a curtain or drapery whose lower border is often more luminous. Several parallel curtains frequently appear at the same time. Near the zenith the curtain may have a fanlike form on account of the perspective.
R (abbr for rays). The rays can be isolated, narrow or broad, short or long. They may appear in great segments or like masses or rays, very often resembling curtains.
C (abbr for corona). When the rays approach the magnetic zenith they seem, on account of the perspective, to converge to this point and form a corona. This may be formed by long rays or by short ones, it may be completed or incomplete. A corona can also be formed by bands, draperies, or more diffuse forms near the magnetic zenith.

.

III. Flaming auroras (abbr F). A characteristic, rapidly moving form, consisting of strong waves of light which move upwards, one after the other, in the direction of the magnetic zenith. The waves have the form of detached arcs which move upwards normally to the direction of the arc; they can be compared to invisible waves illuminating broad rays and patches which appear and disappear rhythmically when the waves pass them. The flaming aurora frequently appears after strong displays of rays and curtains and is often followed by the formation of a corona.

For more information,about auroras, visit Auroras: Paintings in the Sky.

aurora acceleration
   (Earth's Magnetosphere Glossary - GSFC)
Auroral acceleration--The process by which auroral electrons acquire their energies, typically 1-10 keV. May be associated with parallel voltage drops or with an interaction between particles and plasma waves, and may be related to magnetic reconnection in the plasma sheet.
aurora australis
   (NASA SP-7, 1965)
The aurora of the Southern Hemisphere.
aurora borealis
   (NASA SP-7, 1965)
The aurora of northern latitudes. Also called aurora polaris, northern lights .
aurora polaris
   (NASA SP-7, 1965)
= aurora borealis.
auroral electrojets
   (Earth's Magnetosphere Glossary - GSFC)
Two intense electric currents, flowing around the auroral oval from the day side towards the night side and meeting somewhat west of midnight. Associated with Birkeland currents and caused by the unusual electric conductivity properties of ionospheric plasma, the electrojets are responsible for practically all of the magnetic disturbance observed on the ground due to substorms. Their magnitude (derived by analyzing such disturbances) often serves as a convenient gauge of the intensity of substorm activity.
auroral kilometric radiation
   (Earth's Magnetosphere Glossary - GSFC)
Intense radio waves whose wavelength is of the order of a kilometer, emitted from regions above the ionosphere where the aurora is (apparently) accelerated. Since the waves are even longer than those of the AM radio band, they are stopped by the ionosphere and do not reach the ground, but they are readily observed from spacecraft.
auroral oval
   (Earth's Magnetosphere Glossary - GSFC)
The region in which aurora appears at the same time, corresponding to the "ring of fire" around the mmagnetic pole, often observed by satellite cameras. It resembles a circle centered a few hundred kilometers nightward of the magnetic pole, and its size varies with magnetic activity. During large magnetic storms it expands greatly, making auroras visible at regions far from the pole, where they are a rare occurence.
auroral zone
   (NASA Thesaurus / NASA SP-7, 1965)
A roughly circular band around either geomagnetic pole above which there is a maximum of auroral activity. It lies about 10 to 15° of geomagnetic latitude from the geomagentic poles.
The auroral zone broadens and extends equatorward during intense auroral displays. The northern auroral zone is centered along a line passing near Point Barrow, Alaska, through the lower half of Hudson Bay, slightly off the southern tip of Greenland, through Iceland, northern Norway and northern Siberia. Along this line auroras are seen on an average of 240 nights a year. The frequency of auroras falls off both to the north and to the south of this line but more rapidly to the south. The most severe blackouts occur in the auroral zone.
austausch coefficient
   (NASA SP-7, 1965)
= exchange coefficient.
austenite
   (NASA Thesaurus)
A solid solution of carbon in gamma-iron.
austenitic stainless steels
   (NASA Thesaurus)
Steels having at room temperature a microstructure consisting, at least predominantly, of austenite. Their austenitic microstructure is attained above all by alloying conditions, e.g., manganese and nickel.
australite
   (NASA SP-7, 1965)
See tektite.
authorized carrier frequency
   (NASA SP-7, 1965)
A specific carrier frequency authorized for use, from which the actual carrier frequency is permitted to deviate, solely because of frequency instability, by an amount not to exceed the frequency tolerance.
autoconvection gradient
   (NASA SP-7, 1965)
= autoconvective lapse rate.
autoconvective lapse rate
   (NASA SP-7, 1965)
The environmental lapse rate of temperature in an atmosphere in which the density is constant with height (homogenous atmosphere), equal to g/R, where g is the acceleration of gravity and R the gas constant. For dry air the autoconvective lapse rate is approximately +3.4 x 10-4 °C per centimeter. Also called autoconvection gradient.
autocorrelation
   (NASA Thesaurus / NASA SP-7, 1965)
In statistics the simple linear internal correlation of members of a time series (ordered in time or other domains).
autocorrelation function
   (NASA SP-7, 1965)
Autocorrelation for variable lag.
autoigniting propellant
   (NASA SP-7, 1965)
Any propellant that ignites by itself without external stimulation.
autoignition temperature
   (NASA SP-7, 1965)
The temperature at which combustible materials ignite spontaneously in air.
autokinetic illusion
   (NASA SP-7, 1965)
The illusion of a fixed object or light moving when gazed at steadily.
automated en route ATC
   (NASA Thesaurus)
An air traffic control technology which allows computers to make decisions about conflict resolution, the generation of clearances, and their automatic transmission, with the operator standing by to take over in an emergency.
automated guideway transit vehicles
   (NASA Thesaurus)
A system of a large number of captive vehicles traveling at relatively close headways on an exclusive guideway controlled by a computer. Used for AGT.
automated mixed traffic vehicles
   (NASA Thesaurus)
Low speed, surface vehicles automatically operated and controlled in a pedestrian environment by following a buried wire in the roadways sensing obstacles and stopping at predetermined spots for passenger exit and entry. Used for AMTV.
automated pilot advisory system
   (NASA Thesaurus)
An airport advisory system and an air traffic advisory system designed to improve airport and air traffic advisories at high density uncontrolled airports.
automated radar terminal system
   (NASA Thesaurus)
Radar tracking system for use in a terminal area. Primary and secondary radar targets are detected and data for the two are correlated for transmission to a central computer.
automatic celestial navigation
   (NASA SP-7, 1965)
= celestial guidance.
automatic computer
   (NASA SP-7, 1965)
A computer which can automatically perform a comprehensive sequence of operations.
automatic control
   (NASA Thesaurus / NASA SP-7, 1965)
Control of devices and equipment, including aerospace vehicles, by automatic means.
automatic data processing system
   (NASA SP-7, 1965)
An electronic system that includes an electronic data processing system plus auxiliary and connecting communications equipment.
automatic direction finder
   (NASA SP-7, 1965)
(abbr ADF)
A radio direction finder which automatically and continuously provides a measure of the direction of arrival of the received signal. Data are usually displayed visually.
automatic frequency control
   (NASA Thesaurus / NASA SP-7, 1965)
(abbr AFC)
An arrangement whereby the frequency of an oscillator is automatically maintained within specified limits.
automatic gain control
   (NASA Thesaurus / NASA SP-7, 1965)
(abbr AGC)
A process by which gain is automatically adjusted as a function of input or other specified parameter.
automatic pilot
   (NASA Thesaurus / NASA SP-7, 1965)
Equipment which automatically stabilizes the attitude of a vehicle about its pitch, roll, and yaw axes. Also called autopilot .
automatic repeat request
   (NASA Thesaurus)
A request from a receiving device to retransmit the most recent block of data.
automatic stability
   (NASA SP-7, 1965)
Stability achieved with the controls operated by automatic devices, as by an automatic pilot.
automatic tracking
   (NASA SP-7, 1965)
Tracking in which a servomechanism automatically follows some characteristic of the signal; specifically, a process by which tracking or data acquisition systems are enabled to keep their antennas continually directed at a moving target without manual operation.
automatic traffic advisory and resolution
   (NASA Thesaurus)
Ground based collision avoidance system using the surveillance and data link capabilities of the discrete address beacon system (DABS). Used for ATARS.
automatic weather stations
   (NASA Thesaurus)
Weather stations at which the services of observers are not required. They are usually equipped with telemetric apparatus.
autonomous spacecraft clocks
   (NASA Thesaurus)
Standard Time scale instruments aboard spacecraft with provisions for synchronization with existing satellite-based system (global positioning system, for example).
autopilot
   (NASA SP-7, 1965)
= automatic pilot.
autoradiography
   (NASA Thesaurus)
A technique that uses x ray film to visualize radioactivly labeled molecules or fragments of molecules used in analyzing the length and number of DNA fragements separated by gel electrophoresis.
autorotation
   (NASA Thesaurus)
A rotorcraft flight condition in which the lifting rotor is driven entirely by action of the air when the rotorcraft is in motion.
autosyn
   (NASA SP-7, 1965)
(A trade name, from autosynchronous, often capitalized). A remote-indicating instrument or system based upon the synchronous-motor principle, in which the angular position of the rotor of one motor at the measuring source is duplicated by the rotor of the indicator motor, used, e.g., in fuel-quantity or fuel-flow measuring systems, position-indicating systems, etc.
autosynchronous
   (NASA SP-7, 1965)
Full term of autosyn .
autotrophs
   (NASA Thesaurus)
Organisms capable of synthesizing organic nutrients directly from simple inorganic substances such as carbon dioxide and inorganic nitrogen.
autumn
   (NASA Thesaurus)
The season of the year between summer and winter. Its beginning is marked by the autumnal equinox and its end by the winter solstice.
autumnal equinox
   (NASA SP-7, 1965)
1. That point of intersection on the celestial sphere of the ecliptic and the celestial equator occupied by the sun as it changes from north to south declination, on or about September 23. Also called September equinox, first point of Libra .
2. That instant the sun reaches the point of zero declination when crossing the celestial equator from north to south.
auxiliary circle
   (NASA SP-7, 1965)
In celestial mechanics, a circumscribing circle to an orbital ellipse with a radius a, the semimajor axis. The auxiliary circle is related to the ellipse by
QN = Q'N(1 - e2)1/2
where e is the eccentricity; Q is any point on the ellipse; N is the foot of the perpendicular through Q to the line of apsides; and Q' is the intersection of the perpendicular and the auxiliary circle.
auxiliary fluid ignition
   (NASA SP-7, 1965)
A method of ignition of a liquid propellant rocket engine in which a liquid which is hypergolic with either the fuel or the oxidizer is injected into the combustion chamber to initiate combustion.
Aniline is used as an auxiliary fluid with nitric acid and some organic fuels to initiate combustion.
auxiliary landing gear
   (NASA SP-7, 1965)
That part or parts of a landing gear, as an outboard wheel, which is intended to stabilize the craft on the surface but which bears no significant part of the weight.
auxiliary power unit
   (NASA SP-7, 1965)
(abbr APU)
A power unit carried on an aircraft or spacecraft which can be used in addition to the main sources of power of the craft.
avalanche
   (NASA SP-7, 1965)
The cumulative process in which charged particles accelerated by an electric field produce additional charged particles through collision with natural gas molecules or atoms. See Townsend ionization coefficient.
avalanche diodes
   (NASA Thesaurus)
A solid state device that takes advantage of avalanche multiplication of the photocurrent.
average
   (NASA SP-7, 1965)
= arithmetic mean.
average deviation
   (NASA SP-7, 1965)
In statistics, the average or arithmetic mean of the deviations, taken without regard to sign, from some fixed value, usually the arithmetic mean of the data. Also called mean deviation . See standard deviation.
average information content
   (NASA SP-7, 1965)
The average of the information content per symbol emitted from a source. Also called entropy and negentropy .
aviation medicine
   (NASA SP-7, 1965)
See aerospace medicine.
aviation meteorology
   (NASA Thesaurus)
Weather conditions and meteorological studies pertaining to aeronautics.
avionics
   (NASA Thesaurus)
The use of electronics in all its forms in airborne or aerospace vehicles.
Avogadro's constant
   (NASA SP-7, 1965)
= Avogadro's number.
Avogadro's law
   (NASA SP-7, 1965)
See Avogadro's number.
Avogadro's number
   (Plasma Physics and Fusion Energy Glossary)
N = 6.0221367 x 10^23, uncertainty of .59 parts per million. Number of particles in a mole of a substance. Coefficient relating Boltzmann's constant to the ideal gas constant. This is the number of atoms per gram-atom.
Avogadro's number
   (NASA SP-7, 1965)
(symbol NA)
The number of molecules in 1 mole of gas (6.02252 X 1023 per mole).
That this number is a constant for permanent gases is the Avogadro law: under normal conditions, i.e., pressure of 1 standard atmosphere and temperature of 0° C, the volume occupied by 1 mole of gas is the same for all permanent gases (22,414 cubic centimeters). See Loschmidt number.
awards
   (NASA Thesaurus)
Distinctions that are bestowed upon a person or persons due to their special contributions to a field.
axial flow compressor
   (NASA SP-7, 1965)
A rotary compressor having interdigitated rows or stages of rotary and of stationary blades through which the flow of fluid is substantially parallel to the rotor's axis of rotation. Compare centrifugal compressor.
axial modes
   (NASA Thesaurus)
Regimes of vibration along a given axis.
axial strain
   (NASA Thesaurus)
Linear strain in a plane parallel to the longitudinal axis of the specimen. Used for axisymmetric deformation and uniaxial strain.
axis (plural axes)
   (NASA SP-7, 1965)
1. A straight line about which a body rotates, or along which its center of gravity moves (axis of translation).
2. A straight line around which a plane figure may rotate to produce a solid; a line of symmetry.
3. One of a set of reference lines for a coordinate system.
axis of freedom
   (NASA SP-7, 1965)
Of a gyro, an axis about which a gimbal provides a degree of freedom.
axis of thrust
   (NASA SP-7, 1965)
= thrust axis.
axisymmetry
   (Plasma Physics and Fusion Energy Glossary)
Geometric property of a system which is symmetric about an axis of rotation. For example, an ideal circular torus is symmetric about the axis running through the center of the torus (like the axle of a wheel)
AZ
   (Space Flight Glossary - JPL)
Azimuth.
azimuth
   (NASA Thesaurus / NASA SP-7, 1965)
1. Horizontal direction or bearing. Compare azimuth angle.
2. In navigation, the horizontal direction of a celestial point from a terrestrial point, expressed as the angular distance from a reference direction, usually measured from 0° at the reference direction clockwise through 360°.
An azimuth is often designated as true, magnetic, compass, grid, or relative as the reference direction is true, magnetic, compass, grid north, or heading, respectively. Unless otherwise specified, the term is generally understood to apply to true azimuth, which may be further defined as the arc of the horizon, or the angle at the zenith, between the north part of the celestial meridian or principal vertical circle and a vertical circle, measured from 0° at the north part of the principal vertical circle clockwise through 360°.
3. In astronomy, the direction of a celestial point from a terrestrial point measured clockwise from the north or the south point of the meridian plane. See horizon system.
4. In surveying, the horizontal direction of an object measured clockwise from the south point of the meridian plane.
In surveying, an azimuth of a celestial body is called an astronomic azimuth.
azimuth
   (Global Land Information System Glossary - USGS)
Azimuth is the angle of horizontal deviation, measured clockwise, of a bearing from a standard direction.
azimuth angle
   (NASA SP-7, 1965)
1. Azimuth measured from 0° at the north or south reference direction clockwise or counterclockwise through 90° or 180°.
Azimuth angle is labeled with the reference direction as a prefix and the direction of measurement from the reference direction as a suffix. Thus, azimuth angle S 144° W is 144° west of south, or azimuth 324°. When azimuth angle is measured through 180°, it is labeled N or S to agree with the latitude and E or W to agree with the meridian angle.
2. In surveying, an angle in triangulation or in traverse through which the computation of azimuth is carried.
azimuth error
   (NASA SP-7, 1965)
An error in the indicated azimuth of a target detected by radar, resulting from horizontal refraction. Compare range error.
Inasmush as significant gradients of index of refraction are very uncommon in the atmosphere, these errors almost invariably are negligible. Seacoast areas may give rise on occasion to appreciable horizontal bending of radio waves because of the contrast of refractive index values between the air over land and the air over water.
azimuth marker
   (NASA SP-7, 1965)
1. A scale encircling the plan position indicator (PPI) scope of a radar on which the azimuth of a target from the radar may be measured.
2. Reference limits inserted electronically at 10° or 15° intervals which extend radially from the relative position of the radar on an off center PPI scope. These are employed for target azimuth determination when the radar position is not at the center of the PPI scope and hence the fixed azimuth scale on the edge of the scope cannot be employed.
On such markers north is usually 0°, east 90°, etc. Occasionally, on ship or airborne radars, 0° is used to indicate the direction in which the craft is heading, in which cases the relative bearing, not azimuth, of the target is indicated.
azoles
   (NASA Thesaurus)
Compounds that contain a five-membered heterocylic ring containing one or more nitrogen atoms.
azran
   (NASA SP-7, 1965)
Azimuth and range.
This term was coined in the field of radar, and has since been extended in application to the locating of any object (or target) by means of polar coordinates.
Azusa
   (NASA SP-7, 1965)
A short-baseline, continuous wave, phase comparison, single-station, tracking system operating at C-band and giving two direction cosines and slant range which can be used to determine space position and velocity.