First Flight Results on Time-Optimal Spacecraft Slews

This paper describes the design and flight implementation of time-optimal attitude maneuvers performed onboard NASA’s Transition Region and Coronal Explorer spacecraft. Minimum-time reorientation maneuvers have obvious applications for improving the agility of spacecraft systems, yet this type of capability has never before been demonstrated in flight due to the lack of reliable algorithms for generating practical optimal control solutions suitable for flight implementation. Constrained time-optimal maneuvering of a rigid body is studied first, in order to demonstrate the potential for enhancing the performance of the Transition Region and Coronal Explorer spacecraft. Issues related to the experimental flight implementation of time-optimal maneuvers onboard Transition Region and Coronal Explorer are discussed. A description of an optimal control problem that includes practical constraints such as the nonlinear reaction wheel torque-momentum envelope and rate gyro saturation limits is given. The problem is solved using the pseudospectral optimal control theory implemented in the MATLAB® software DIDO. Flight results, presented for a typical large-angle time-optimal reorientation maneuver, show that the maneuvers can be implemented without any modification of the existing spacecraft attitude control system. A clear improvement in spacecraft maneuver performance as compared with conventional eigenaxis maneuvering is demonstrated.