Space-Based, Long-Distance Laser Pointing and Tracking

摘要

To rapidly and reliably acquire and maintain a laser on a long- distance, space-based target (or receiver), a pointing system capable of locking onto the position of a target (or receiver) over a wide field-of-view has been developed. The pointing/tracking system consists of a highly instrumented hexapod platform, a six-legged parallel kinematic machine capable of six degree- of-freedom (DOF) motion. This architecture is lightweight, highly fault tolerant, and capable of absorbing vibrations in all six DOF so off-axis vibrations do not induce on-axis errors through structural flexibilities. Accelerometers are used to measure ambient vibrations and reject them using an active control system. Optical sensors are used to measure pointing errors and reject them using decoupled, fault tolerant feedback control techniques. New models and control algorithms have been developed utilizing these measurements to provide tracking in a fault tolerant manner over a wide field-of-view. The control advances include: 1) Design criteria to maximize the hexapod's performance; 2) Decoupled control algorithms that result in high bandwidths for any rigid payload; 3) Optimal methods of reconfiguring the control following failures; 4) Methods for managing the overlapping capabilities of coarse and fine stages; 5) Adaptive algorithms to enhance rejection of monotone vibrations; and 6) Estimation algorithms to accurately identify the payload. Six DOF vibrations have been generated using a second hexapod, and robust force control algorithms have been employed to de-sensitize its control to payload structural dynamics.