Attitude Stabilization of the GEOS-C Spacecraft.

The report discusses some of the alternatives available in the design of the attitude control system on GEOS-C. The experiments currently under consideration require earth pointing accuracy to several distinct levels of accuracy. A radar altimeter whose purpose is to measure the height of the spacecraf above the geoid imposes a stabilization requirement more severe than on any of the previous GEOS spacecraft. An attitude control system similar to those cmployed in GEOS-1 and -2 is optimized for the GEOS-C orbit. Studies are then made to determine the stabilization improvement when this system is augmented first by a constant speed rotor and then by a rotor whose angular velocity is modulated in fidelity with the mean anomaly. In this latter case, it is demonstrated that earth pointing accuracy can be maintained to less than one degree more than 99 of the time. This, however, does not take into account any offset of the antenna boresight from the longitudinal principal axis of inertia. Author