"This document ANSVAIAA R-004-1992 gives basic definitions and deals with the motion of flight vehicles relative to various inertial axis systems or relative to the atmosphere@ which may be assumed to be at rest or in translational motion at constant velocity relative to the Earth. The flight vehicle is assumed to be rigid; however@ most of the definitions can be applied to the case of a flexible flight vehicle. The vehicle may be in orbit or free flight@ or may be in contact with the ground@ or a carrying vehicle. The carrying vehicle may be a flight vehicle itself or a ground launcher. When account is taken of the variations at the Earth's surface in the direction of the vertical (local direction of acceleration due to gravity)@ the term given in the sub-clauses and figures in question is qualified by the term ""local."" See Appendix D.l for a discussion of the astronomical standards for the definition of inertial axis systems. "