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

Attitude determination of satellites is normally the job of inertial instruments, such as gyroscopes, or through sensing instruments, such as star trackers orGlobal Positioning Satellites (GPS). Satellite health monitoring systems watch and determine if the satellite deviates from its normal operating attitudeorientation. 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 area 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 determineddirectly from telemetry data of the attitude control systems and an accurate spacecraft model. The fidelity of a satellite attitude determination model requiredto get reasonable predictions from using only telemetry data of the attitude controllers, such as thruster on/off indicators and reaction wheel rotor speeds, isinvestigated. Experimental tests using telemetry data received from the Air Force Institute of Technology's (AFIT) Simulated Satellite, SimSat, is used inverifying a Matlab model which outputs SimSat's orientation from SimSat's reaction wheel and thruster telemetry data. Software modeling results showed thatit is possible to determine a satellite's attitude from only the attitude controllers' telemetry data when the satellite's dynamic model is known.