The increasing demand for high precision spacecraft attitude and orbit maneuvers puts very strict requirements on thrusters and their control. Best suited for this task are proportional thrusters able to produce precise micronewton thrust levels with very little noise. Such thrusters under current development are cold gas microthrusters, field emission electric propulsion (FEEP), colloid thrusters and micro-resistojets, with ion engines and Hall thrusters having attractive properties should a miniaturization be possible. Optimal utilization of proportional thrusters can be achieved by minimizing the 1-norm, 2-norm or infinity-norm of the thrust command vector, resulting in a minimum flow rate controller, a minimum power controller or a minimum force controller respectively. The first and last are found by solving linear programs, the middle by using the pseudoinverse of the thruster configuration matrix along with a bias. The control authority, which is the maximum performance of a thruster system, can be found by maximizing the force and torque output. A single number, referred to as the minimum control authority, measures the weakest output of the thruster system. All of these concepts are given a thorough review, and the thesis rounds off by implementing them on the LISA Pathfinder mission. Calculations show the algorithms to work well, but a more efficient way of finding the minimum control authority is desirable.
Author: Johansson, Henrik
Source: Lulea University of Technology
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