Ground and Space Testing of Multiple Spacecraft Control During Close-Proximity Operations

Abstract

A multiple spacecraft close-proximity control algorithm was implemented and tested with the Synchronized Position Hold Engage and Reorient Experimental Satellites (SPHERES) facility onboard the International Space Station (ISS). During flight testing, a chaser satellite successfully approached a virtual target satellite, while avoiding collision with a virtual obstacle satellite. This research contributes to the control of multiple spacecraft for emerging missions, which may require simultaneous gathering, rendezvous, and docking. The unique control algorithm was developed at NPS and integrated onto the MIT SPHERES facility. The control algorithm implemented combines the efficiency of the Linear Quadratic Regulator (LQR), and the robust collision avoidance capability of the Artificial Potential Function method (APF). The LQR control effort serves as the attractive force toward goal positions, while the APF-based repulsive functions provide collision avoidance for both fixed and moving obstacles. The amalgamation of these two control methods into a multiple spacecraft close-proximity control algorithm yielded promising results as demonstrated by simulations performed at NPS. Comprehensive simulation evaluation enabled implementation and testing of the spacecraft control algorithm on the SPHERES facility at MIT. Finally, successful ground testing enabled execution of flight testing onboard the ISS. The NPS’s Spacecraft Robotics Laboratory (SRL) and MIT’s Space Systems Laboratory (SSL) simulations, the MIT’s SSL SPHERES ground testing, and the SPHERES flight testing results are all presented in this paper.