Closed-Loop Control of Autonomous Spacecraft by Matt Jeffrey
The goal of this research is to understand how process noise and process bias can degrade the performance of formations
of spacecraft, as well as autonomous spacecraft following trajectories, and to develop control
algorithms that minimize these effects. The measures of performance are 1) fuel usage and 2) state error.
This research involves performing experiments on the Synchronized Position Hold Engage and Reorient Experimental
testebed. There are currently three SPHERES satellites onboard the International Space Station. Each
satellite has twelve thrusters that are used to impart
specific ΔV's when commanded by a control algorithm.
The current implementation of the low-level thrust controller is open-loop and frequently leads to errors in the actual
delivered ΔV; it is based on an idealized force/torque model. The performance gains resulting from the reduction of these
errors is under investigation while a new, closed-loop thrust controller is developed. The new controller utilizes onboard
accelerometers and gyros to monitor the performance of the thrusters in real-time, and attempts to more accurately apply ΔV
commands. The overall performance improvements in fuel use and trajectory tracking are studied.
The image below (Courtesy of NASA) shows the U.S. astronaut and MIT alum Dan Tani observes a SPHERES
under closed-loop control on the ISS, in December 2007.