Intelligent Guidance and Trajectory Command Systems for Autonomous Space Vehicles

This effort represents continued developments of an integrated reconfigurable control, adaptive guidance, and onboard trajectory command reshaping system that was successfully flight tested in 2003. The purpose of these advanced algorithms is to recover the mission in the face of severe off-nominal conditions and control effector failures. In the flight test program, the system was developed for the mission's final flight phase known as approach and landing. The current effort is furthering the technology with application to other flight phases such as re-entry and Terminal Area Energy Management (TAEM). The guidance law utilizes a backstepping architecture to generate attitude rate commands that drive the inner-loop control system. Under certain control surface failure conditions, the bandwidth of the inner-loop control system is purposely reduced to lessen the commanded moments. In these cases, the guidance feedback gains are adapted on-line to preserve stability margins in the guidance loops in the face of degraded maneuvering capabilities. During the course of the flight test program, it was shown that failure scenarios that significantly alter the energy management of the vehicle will require the commanded trajectory to be reshaped in order to achieve an acceptable touchdown - even with reconfigurable/adaptive control and guidance. The onboard trajectory reshaping algorithm is known as the Optimum-Path- To-Go (OPTG) approach. OPTG results from the flight test program will be reviewed. However, new results of trajectory command reshaping during the TAEM guidance flight phase will also be presented. In this flight phase, the altitude and velocity must be brought to acceptable values at the start of the final approach. Further, the Heading Alignment Cone, or HAC turn, is flown to align the vehicle's heading with the runway centerline. It will be shown that the OPTG algorithm can successfully reshape the HAC turn due to significant changes in the vehicle's lift and drag. These changes may come about due to a control effector failure or significant head or tail winds. It will be shown that the mission is able to achieve an acceptable TAEM/final approach interface with trajectory reshaping.