Adaptive control for post-dock maneuvers with an unknown semi-cooperative object

Abstract

Autonomous docking in space has been demonstrated on numerous occasions. These missions have relied on detailed information about the target vehicle for success. However, for autonomous docking applications such as spacecraft servicing, debris capture, and space robotics operations, unknown and changing parameters stress current attitude control systems. Adaptation may assist with control under such conditions. This paper explores the trade-space in which an adaptive controller can maintain attitude control authority when a spacecraft joins with an object with limited physical parameter information, with the goal of charting a path for controller validation via future spaceflight experimentation. Controller analysis and test are based on working with the Synchronized Position Hold Engage Reorient Experimental Satellite (SPHERES) testbed developed at MIT and now a facility of the International Space Station (ISS) National Laboratory managed by NASA Ames Research Center. A comparison is made between a baseline attitude and position proportional-integral-derivative (PID) control system and an adaptive PID approach. The jointed spacecraft inertia, mass, and location of center of mass, are varied to assess the limitations, performance and robustness of these controllers. Attention is given to identifying the most pressing areas for improvement. Conclusions are drawn from both simulation and three degree of freedom ground testing using the SPHERES.