Time-optimal reorientation of a spacecraft using a direct optimization method based on inverse dynamics

This paper proposes a rapid attitude trajectory generation method for satellite reorientation that satisfies the spatial and temporal constraints imposed by the problem of docking with a tumbling object. The problem is first formulated and solved using known academic software readily used for generating optimal guidance trajectories off-line. Then, the problem is reformulated using a polynomial structure that lends itself to satisfying special mathematical constraints imposed by using a unit quaternion for orientation description. The speed profile of the maneuver is varied in order to arrive at a quasi-optimal solution that is both feasible and exactly matches the endpoint conditions specified in the problem. The reduction in the number of varied parameters due to the predetermined structure of the trajectory leads to a faster computational speed as well as having a trajectory that satisfies the end constraints at each iteration. The paper ends with a discussion of solutions obtained for several cases.