Performance Determination of a Multi-Mode Thruster Using GPS and Star Tracker Data

A key element of the Advanced Propulsion Experiment (APEX) spacecraft mission is the accurate thrust determination of a Multi-Mode Ionic Monopropellant Electrospray (MIME) thruster payload. The MIME thruster payload operates in high thrust, low specific impulse chemical mode and low thrust, high specific impulse electric mode, making standard thrust determination processes by accelerometer or attitude maneuver infeasible. The development of a batch filter to determine thrust from an orbit changing maneuver is presented. The batch filter estimates a constant thrust magnitude along with the dynamic states of the vehicle, the coefficients of drag and solar reflectivity and the time biases of the GNSS receiver. To improve accuracies in GPS pseudorange measurements, the International GNSS Service Final Product GPS ephemeris and clock biases are used to improve position and thrust determination. The statistical consistency of the batch filter was verified using a Monte Carlo analysis. An initial investigation of desired maneuver duration and attitude was performed in order to assist in APEX mission design and concept of operations development.