Optimal spacecraft reorientation for earth orbiting clusters: applications to Techsat 21

Aperture synthesis using distributed satellite systems opens up new challenges for designing propulsive maneuvering algorithms as well as orbital configurations. The ability to place these individual satellites in their desired locations is directly related to the overall performance of the system. This paper discusses such issues and determines the optimal cluster trajectories for problems ranging from cluster initialization to cluster reorientation for minimum energy problems. The determination of these optimal trajectories is based upon the calculus of variation approach. As in most optimal control problems, determination of the costates is not an easy task. Assuming time-invariant first-order dynamics (Hill's Equations) leads to a simple linear quadratic tracking problem, thus allowing the co-state trajectories to be estimated. These co-state estimates are then used to determine the optimal trajectories for the clusters through a second-order multiple shooting algorithm. Results specific to cluster initialization and reorientation for the Techsat 21 flight experiment system are presented. It was found that the flight experiment can be initialized rather quickly but a maneuvering time of at least three orbital periods for the geo-location problem is required. (C) 2002 Elsevier Ltd. All rights reserved.