High-accuracy attitude control of satellites in elliptic orbits

A class of feedback attitude-control systems which efficiently result in high-accuracy (10^–4 radians), Earth-pointing motions of satellites of different configurations in elliptic orbits is developed. Gas jets provide the control torque. The state of the attitude motion is assumed to be completely known. Linear differential equations, which have time-varying coefficients and include terms for the gravity torque due to an oblate Earth and terms for the aerodynamic torque, are used to describe the attitude motion when the satellite is practically Earth-pointing. Pontryagin's maximum principle, the necessary conditions for exact solutions of optimal bounded-phase-coordinate problems, and guidelines obtained from the minimum-fuel attitude controls devised for single-axis systems are used in the development. The motions of somestable and someunstable satellites with the developed attitude-control systems are simulated on an analog computer. The overall control system, which is reliable as well as efficient, is simple to realize.This research was sponsored by the National Aeronautics and Space Administration under Grant No. G-133-61.