A general-purpose analog translational trajectory program for orbiting and reentry vehicles

Abstract

Analog computer programs for very complex flight simulations are well known. As a recent example, the complete six-degree-of-freedom equations of motion have been developed by Fogarty and Howe, as well as simple two-dimensional, or two-degree-of-freedom, simulation equations. The former are useful for simulation analyses with a man in the loop, generally in real time. The latter are useful for student analyses of trajectories. The engineering trajectory analyst, however, often appears to be interested additionally in intermediate complexity. He is interested in what we shall call a pseudo-six-degree-of-freedom trajectory program, wherein the three translational degrees of freedom are handled exactly, with all terms included, but the rotational equations of motion are eliminated. In their stead, the analyst inserts arbitrary functions for three angles such as alpha (angle of attack), beta (angle of sideslip), and sigma (roll angle about the velocity with respect to air vector). Such an analytical program turns out to be of great interest in the design phase of an aerospace vehicle, since it permits evaluation of many hardware tradeoffs among different configurations. Such a program, in existence at the Martin Company in digital form since 1964, is described by Wagner and Garner.