Modification of the Cal Poly Spacecraft Simulator System for Robust Control Law Verification

摘要

The Cal Poly Spacecraft Dynamics Simulator, also known as the Pyramidal Reaction Wheel Platform (PRWP), is an air-bearing four reaction wheel spacecraft simulator designed to simulate the low-gravity, frictionless condition of the space environment and to test and validate spacecraft attitude control hardware and control laws through real-time motion tests. The PRWP system was modified to the new Mk.III configuration, which adopted the MATLAB xPC kernel for better real-time hardware control. Also the Litton LN-200 IMU was integrated onto the PRWP and replaced the previous attitude sensor. Through the comparison of various control laws through motion tests the Mk.III configuration was tested for robust control law verification capability. Two fixed-gain controllers, full-state feedback (FSFB) and linear quadratic regulator with set-point control(LQRSP), and two adaptive controllers, nonlinear direct model reference adaptive controller (NDMRAC) and the adaptive output feedback (AOF), were each tested in three different cases of varying plant parameters to test controller robustness through real-time motion tests. The first two test cases simulate PRWP inertia tensor variations. The third test case simulates uncertainty of the reaction wheel dynamic by slowing down the response time for one of the four reaction wheels. The Mk.III motion tests were also compared with numerical simulations as well as the older Mk.II motion tests to confirm controller validation capability. The Mk.III test results confirmed certain patterns from the numerical simulations and the Mk.II test results. The test case in which actuator dynamics uncertainty was simulated had the most effect on controller performance, as all four control laws experienced an increase in steady-state error. The Mk.III test results also confirmed that the NDMRAC outperformed the fixed-gain controllers.