Laboratory Experimentation of Guidance and Control of Spacecraft During On-Orbit Proximity Maneuvers

Abstract

A planar laboratory testbed was introduced for the simulation of autonomous proximity maneuvers of a uniquely control actuator configured spacecraft. The testbed consists of a floating robotic simulator equipped with dual vectorable cold-gas thrusters and a miniature control moment gyro floating via planar air bearings on a flat floor. Inertial position and attitude measurements are obtained with a discrete Kalman filter and linear quadratic estimator for navigation; feedback linearized control coupled with a linear quadratic regulator is used to command the control moment gyro and while the same feedback linearized controller is used coupled with Schmitt triggers and Pulse Width Modulation to command the vectorable thrusters. The presented experimental tests of autonomous closed path proximity maneuvers of the spacecraft simulator offer significant sample cases. The experimental results, which show good repeatability and robustness against disturbance and sensor noise, validate the proposed estimation and control approaches and demonstrate in particular, the small time local controllability of the system, confirming the analytical results. The achieved accuracy in following the reference trajectory (respectively ~ 1 cm for translation and ~ .5 deg for rotation given only the vectorable thrusters as control inputs) demonstrates both a feasible and promising actuator configuration for small spacecraft. NPS SRL's robotic spacecraft simulator testbed, despite its reduction to only 3-DoF, allows experiments to be conducted in a low-risk and relatively low-cost environment where intermediate validation can occur between analytical/numerical simulations and full flight proximity navigation missions. Furthermore, the controllability analysis and the algorithms proposed for the state estimation and control can be in principle extended to full-fidelity 6DoF spacecraft applications. The next step in this ongoing research will focus on the expansion of the presented analytical methods for non-linear control-affine systems with drift to numerical simulations on a full 6-DoF spacecraft model as well as work to develop further controllers that can take advantage of the minimum number of control actuator configuration of only two thrusters and no momentum exchange devices.