An orbit in which gravitational influences are used to induce a precession in a satellite's orbital plane.

An item kept available to replace an item which fails to perform satisfactorily.

The science that deals with the motion, behavior, appearance or modification of missiles acted upon by propellants, rifling, wind, gravity, temperature or other modifying conditions of force.

A unit of pressure equal to one million dynes per square centimeter, or 0.99 atmospheres.

A large, >200 km, circular depression from the explosive impact of an asteroid or similar sized body on a planet surface, usually rimmed by mountains.

A rocket propellant consisting of two unmixed or uncombined chemicals (fuel and oxidizer) fed separately into the combustion chamber.

Two stars revolving around a common center of gravity.

A basic unit of computer information; abbreviation of binary digit.

A mixture of saltpeter (potassium nitrate), sulfur, and charcoal, used in explosives and as an early propellant for rockets.

A temporary loss of radio communications which occurs between a spacecraft reentering the atmosphere and ground stations due to an ionized sheath of plasma which develops around the vehicle.