AEROSPACE-GLOSSARY
A
Source edition 1965. Please read the Introduction to find out about this dictionary and our plans for it. Caution, many entries have not been updated since the 1965 edition.
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aberration
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 = constant of aberration
ablate
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 material
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.
ablating nose cone
A nose cone designed to reduce heat transfer to the internal structure by the use of an ablating material.
ablation
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 ablating material.
ablatively
By a process of ablation, as in ablatively cooled .
ablative material = ablating material.
ablator
A material designed to provide thermal protection through ablation.
abort
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.
Abridged Nautical Almanac
See Nautical Almanac.
absolute
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
An instrument intended to give acceptably accurate, direct indications of absolute altitude.
absolute altitude
Altitude above the actual surface, either land or water, of a planet or natural satellite. Compare true altitude.
absolute coordinate system
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
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
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 = index of refraction (sense 1).
absolute instrument
An instrument whose calibration can be determined by means of physical measurements on the instrument. Compare secondary instrument.
absolute magnitude (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.