Flight-like ground demonstration of precision formation flying spacecraft

Abstract

Initial high-fidelity, flight-like ground demonstrations of precision formation flying spacecraft are presented. In these demonstrations, maneuvers required for distributed spacecraft interferometry, such as for the Terrestrial Planet Finder Interferometer, were performed to near-flight precision. Synchronized formation rotations for "on-the-fly" observations require the highest precision. For this maneuver, ground demonstration performance requirements are 5 cm in relative position and 6 arc minutes in attitude. These requirements have been met for initial demonstrations of formation-keeping and synchronized formation rotations. The maneuvers were demonstrated in the Formation Control Testbed (FCT). The FCT currently consists of two, five degree-of-freedom, air bearing-levitated robots. The final sixth degree-of-freedom is being added in August 2007. Each robot has a suite of flight-like avionics and actuators, including a star tracker, fiber-optic gyroscopes, reaction wheels, cold-gas thrusters, inter-robot communication, and on-board computers that run the Formation and Attitude Control System (FACS) software. The FCT robots and testbed environment are described in detail. Then several initial demonstrations results are presented, including (i) a sub-millimeter formation sensor, (ii) an algorithm for synchronizing control cycles across multiple vehicles, (iii) formation keeping, (iv) reactive collision avoidance, and (iv) synchronized formation rotations.