Attitude Model of a Reaction Wheel/Fixed Thruster Based Satellite Using Telemetry Data

摘要

Attitude determination of satellites is normally the job of inertial instruments, such as gyroscopes, or through sensing instruments, such as star trackers or Global Positioning Satellites (GPS). Satellite health monitoring systems watch and determine if the satellite deviates from its normal operating attitude orientation. Knowing the orientation of a satellite is essential in being able to control it in order to complete the satellite's designated mission. While there are a multitude of ways to determine a satellite's orientation, very little research has been done on determining if the attitude of a satellite can be determined directly from telemetry data of the attitude control systems and an accurate spacecraft model. The fidelity of a satellite attitude determination model required to get reasonable predictions from using only telemetry data of the attitude controllers, such as thruster on/off indicators and reaction wheel rotor speeds, is investigated. Experimental tests using telemetry data received from the Air Force Institute of Technology's (AFIT) Simulated Satellite, SimSat, is used in verifying a Matlab model which outputs SimSat's orientation from SimSat's reaction wheel and thruster telemetry data. Software modeling results showed that it is possible to determine a satellite's attitude from only the attitude controllers' telemetry data when the satellite's dynamic model is known. Testing involving SimSat showed that attitude determination from the Matlab model is possible but not perfect. Additional information needs to be known about the satellite's systems and characteristics and about the environment in which the satellite operates, in order to increase the fidelity of the model for more accurate predictions of the satellite's attitude. Even though more research is needed, there is promise for using satellite attitude controllers fields such as health monitoring.