Design and implementation of the state estimator for trajectory following of an electromagnetic formation flight testbed

Abstract

Formation fight of multiple satellites is an attractive concept for achieving complicated space missions that are di±cult or impossible with a single monolithic satellite. Since traditional thrusters require propellant consumption for maintaining the formation of multiple satellites, one concern is the way of more efficiently generating thrust. A plausible concept for the alternative actuator is Electromagnetic Formation Flight (EMFF), which uses the electromagnetic force generated by superconducting magnets and the reaction torque generated by reaction wheels as the way to control position and attitude of each satellite respectively. Since all of the actuators in EMFF utilize solar energy and do not depend on consumables, the mission lifetime can be substantially increased. The Space Systems Laboratory at Massachusetts Institute of Technology has contributed to demonstrating the concept of EMFF by developing a testbed composed of two vehicles, and the mission for one moving vehicle to hold its position with respect to the other stationary vehicle on a plane was successfully achieved. In this thesis, it is pursued to experimentally show that the electromagnetic force is a su±cient control actuator for a trajectory following mission with a new state estimator designed for the mission. Firstly, the vehicle of the testbed is categorized into three subsystems of °ight computer, actuator, and measurement system, each of which is described in detail. Then, the new state estimator is designed with an extended Kalman filter algorithm, and the method to pre-filter erroneous ultrasound measurements is proposed. Its convergence is shown by simulation. Finally, the new state estimator is implemented in the testbed, and the experimental results for several kinds of sinusoidal commanded trajectories are presented, which shows the desired mission is successfully accomplished.