GENERIC DRAG FREE CONTROL SIMULATION - LESSONS LEARNED FROM GRAVITY PROBE B

A generic drag-free simulator has been developed to aid in the design, on-orbit and post-mission data analysis phases of scientific satellite missions. Adaptable to missions as different in nature as Gaia (Global. Astrometric Interferometer for Astrophysics) and STEP (Satellite Test of the Equivalence Principle), this simulator will provide necessary modeling capability to increasingly complex future missions. A complete mission software simulator including controls, full-body dynamics and comprehensive spacecraft environment disturbances has been established for Gravity Probe B (GP-B). Reproduction of the mission is being carried out to validate the simulator with actual flight data and refine the underlying models. The importance of this effort lies in the challenge to meet rising science requirements in the area of maximum disturbance rejection. Future missions such as Gaia, STEP, LISA (Laser Interferometer Space Antenna) and others require a minimum of 3 orders of magnitude improvement over the GP-B performance of 10(-9) m/sec(2). While technology advancements will certainly be required to achieve these levels, it became increasingly clear to the scientists and engineers who delivered the GP-B results that the ability to monitor and adjust the coupling of spacecraft to subsystem controllers, at all stages of the mission is essential to optimizing mission results. We provide a look at the progress to date of this effort.