Motion simulator facility for spacecraft attitude control evaluation

Abstract

T be completely meaningful, the development program for a spacecraft attitude control system (ACS) should include demonstrations of attitude acquisition from specified initial conditions, static pointing accuracy under anticipated disturbances, dynamic accuracy under specified commands, control response time, and control stability under changing vehicle dynamics. The effects of nonlinearities and crosscouplings in the control equipment and in the controlled vehicle should be identified in such a development program. A facility that can perform these functions and be used for these purposes is shown in Fig. L Its focal point is a threeaxis motion simulator (TAMS) utilizing gas bearings for support and d.c. torque motors for direct driving on all 3 axes. These essential components of a typical ACS and of the TAMS facility are shown in a simplified block diagram of Fig. 2. The test vehicle to which the components are attached, is mounted on the platform on the inner axis of the motion simulator. Sensors are oriented on the test vehicle so as to be aligned with their respective simulators as required by governing control laws. Output signals from the various sensors are supplied to the on-board computational electronics. Actual torquing devices are generally not used with the packages under test because their torque output is too small to have any significant effect on the d.c. torque motor output of the simulator. A hybrid computer that is a part of the facility is mechanized to receive the torque-required signals from the on-board electronics. It calculates the effect upon the spacecraft (i.e., rate and position) considering such physical parameters as inertia, solar pressure area, vehicle and