MIL-HDBK-143A
A
aam * - Air-to-air missile. See: missile, air-to-air.
aberration - The phenomenon caused by rotation of the earth in its orbit which is sufficient to
cause the light from a star to appear to shift forward. For those stars at right angles to the
direction of the earth's travel, the maximum effect is 20.5 seconds of arc.
ablation - The wearing away of surface material due to the action of the fluid moving past it at
either high speed or high temperature, or both. Ablation is used as a method of removing the
aerodynamic heating effects on missile nose cones during re-entry. Using the ablative
approach, the nose cone material is subjected to thermal degradation involving pyrolysis,
depolymerization, melting, vaporization, and combustion with a resulting continuous removal
of material.
ablative materials - Special materials on the surface of a spacecraft which can be sacrificed -
i.e., carried away or vaporized - during re-entry into the atmosphere. Kinetic energy is
dissipated and excessive heating of the main structure of the spacecraft is prevented.
abort - To cause a Guided Missile to fall short of its mission for any reason other than enemy
action. It may occur at any point after the firing command and before the missile reaches the
target.
absolute altitude- The height or altitude of an object considering, as a base of reference, the
surface terrain over which the object is located.
absolute velocity - The highest velocity theoretically attainable (i.e., the velocity of light 3 x
10
l0 cm/sec).
acceleration blowout -Inadvertent loss of combustion in a turbojet engine incident to an
attempted acceleration and overrich fuel mixture. Also called flameout (which see).
acceleration feedback - A sensing system for control of a missile by elimination of body-
bending effects and maintenance of angles of attack at predetermined values. Accelerometers
are used to sense body accelerations which are fed into the control system for correction of the
motion.
Accelerometer, Guided Missile - An instrument designed to measure one or more acceleration
components of a Guided Missile.
Accelerometer, integrating - An acceleration-measuring device whose output signals are
either proportional to vehicle velocity or to distance traveled, and which performs an
integrating function to achieve these outputs. When used in a Rocket or missile, the
integrating Accelerometer may be preset to reduce fuel flow when the programmed speed has
been achieved.
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