Optimal thruster actuation in high precision attitude and
orbit control systems

Abstract: 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.