  This paper presents a time-constrained model predictive control strategy for
the 6 degree-of-freedom (6DOF) autonomous rendezvous and docking problem
between a controllable "deputy" spacecraft and an uncontrollable "chief"
spacecraft. The control strategy accounts for computational time constraints
due to limited onboard processing speed. The translational dynamics model is
derived from the Clohessy-Wiltshire equations and the angular dynamics are
modeled on gas jet actuation about the deputy's center of mass. Simulation
results are shown to achieve the docking configuration under computational time
constraints by limiting the number of allowed algorithm iterations when
computing each input. Specifically, we show that upwards of 90% of computations
can be eliminated from a model predictive control implementation without
significantly harming control performance.
