Starlight pointing subsystem for the formation interferometer testbed (FIT)

StarLight is a NASA/JPL sponsored mission that will be the first spaceborne stellar interferometer. The objective of the mission is to develop and test technologies for performing interferometric observations in space and for the extremely precise formation flying required to make the instrument work. The Formation Interferometer Testbed (FIT) is a ground based prototype of the two spacecraft StarLight instrument. In this paper a complete model of the FIT pointing system is characterized that includes backlash in the siderostat (SD), hysteresis in the PZT actuators of the fast steering mirrors (FSM), time delays, and air path disturbances. Based on this model, a dual stage pointing controller is designed that achieves a bandwidth sufficient to satisfy the pointing requirement. Simulated and experimental results are given that validate the performance of the pointing system.