Minimum fuel techniques for a space robot simulator with a reaction wheel and PWM thrusters

Space simulators offer engineers great advantages on studying space-related dynamic behavior without actually having to travel into space. They can test various control and design strategies, leading to close-to-optimal spacecraft missions. In this paper, an air-bearing planar space simulator developed for the experimental study of space robots on orbit is briefly presented. To achieve proportional control of 2-way on-off solenoid valves used for robot propulsion, a voltage PWM actuation is employed. The resulting thrust is analyzed, nonlinear valve effects are identified, and techniques tackling their shortcomings are proposed. The experimentally obtained thruster behavior is used to address a minimum fuel nozzle consumption problem during point-to-point robot motions. A comparison between the thruster-only propulsion method with one which includes a reaction wheel follows. A control algorithm for the simultaneous employment of thrusters and reaction wheel is presented. It is found that under certain assumptions, the use of a reaction wheel further minimizes fuel consumption, increasing the useful life of a space robot.