THE COMSAT ATTITUDE AND ORBIT CONTROL SYSTEM FLIGHT SIMULATOR

Abstract

The success of a communications satellite mission depends not only on the proper operation of the on-board Attitude and Orbit Control System (AOCS), but also on the complex interaction between the spacecraft and the ground control center. In support of a satellite program from its inception to launch and throughout the inorbit life, COMSAT has developed a SATELLITE ATTITUDE AND ORBIT CONTROL SYSTEM FLIGHT SIMULATOR. This paper describes the design and operations of the COMSAT FLIGHT SIMULATOR. The simulator is a real-time, high fidelity, operator interactive, spacecraft hardware in the loop system. The heart of the system is a high precision minicomputer in which the spacecraft dynamics, sensors, actuators and most likely failure modes are modeled. A significant feature of the simulator is a faithful duplication of the command and telemetry functions. The operator can send commands and review telemetered data in the same format as during the mission. The simulator operates in real-time and is flexible enough to either simulate or fully integrate parts of the flight hardware. Such is the case for instance for the on-board computer with its complex programmable control algorithms. However, flight hardware in the loop is in no way limited to any particular unit of the flight subsystem. The simulator can also be remotely linked to the ground station and use actual commands as direct inputs for its operation. A colorgraphics driven by the simulated dynamics displays the spacecraft motions and warns the operator of eventual losses of telemetry and command capabilities during attitude anomalies. Following is a partial list of the FLIGHT SIMULATOR capabilities. S Provide an independent means to evaluate and validate a control system design; S Support the development of Control Center (hardware and software) and serve as a training facility for the control operators; S Develop and verify the spacecraft sequence of events; S Help in developing and evaluating, in real time, the on-orbit Operational and Recovery Procedures; S Maximize satellite life through maneuver optimization, and S Support the satellite mission throughout the spacecraft life, providing a test bed for flight anomaly investigation. This last point is significant since, in general, a satellite operator has no guarantee as to the availability of a spacecraft manufacturer’s facility for the full duration of a satellite mission. The COMSAT FLIGHT SIMULATOR is fully operational and is already supporting the STC/DBS (Satellite Television Corporation/Direct Broadcast Satellite) program. COMSAT concurrently developed a flight simulator for INTELSAT VI. These two simulators represent second-generation designs compared to the first real-time, hardwarein-the-loop simulator which was built for INTELSAT V.