Dynamic ground testing of the Skipper Attitude Control System

The evaluation of the Attitude Control System (ACS) for the Skipper spacecraft required the development of two complementary tools: a high fidelity numerical simulation program and a three axis air bearing table to experimentally evaluate the ACS hardware operating in a dynamic environment. The simulation program provides detailed evaluation of the controller's performance over entire orbits, allowing studies of varying sensor viewing conditions, aerodynamic effects and magnetic field variations. The air bearing table was used for functional, rather than calibrated testing of the integrated ACS. The table was first used as a platform for initial integration testing of the ACS sensors, electronics and computer system. The ACS maneuvers were then test-flown on the table. In doing so, several software errors and systemlevel problems were easily identified and corrected. A proposed method for estimating the inertia tensor of the spacecraft in flight was evaluated using air bearing test data. Data gathered from air bearing tests were used to evaluate the attitude determination software off-line. This proved necessary due to a need to examine the attitude resolution algorithm and the lack of a valid indoor GPS signal for nadir vector information.