Adaptive Guidance and Control For Autonomous Launch Vehicles

1 0-7803-6599-2/01/$10.00 © 2001 IEEE 2 Updated October 21, 2000 Abstract—An inverting control system adaptive to failures was recently flight demonstrated on the X-36 unmanned tailless fighter technology demonstrator. This technology has since been applied in simulation to study the potential to improve the performance and reliability of fully reusable launch vehicles. A new technique known as pseudo-control hedging was developed and applied in the latter application to prevent the adaptive law from “seeing” and adapting to vehicle input characteristics such as actuator position limits, actuator rate limits and linear input dynamics. For rocket powered launch vehicles, a recoverable failure will generally lead to a reduction in total control authority. Adaptive guidance technology is required to realize the potential of adaptive control and to overcome potential failures in autonomous launch systems. In this paper, the authors have applied the technique of pseudo-control hedging to implement a fully integrated approach to direct adaptive guidance and control. An adaptive inner-loop provides fault tolerance as in previous applications. An adaptive outerloop is introduced that provides closed-loop guidance for tracking of a reference trajectory. The outer-loop adapts to force perturbations, while the inner-loop adapts to moment perturbations. The outer-loop is “hedged” to prevent adaptation to inner-loop dynamics. The hedge also enables adaptation while at control limits, and eliminates the need for time-scale separation of inner and outer-loop dynamics, which is potentially important for abort scenarios. Adaptation provides time for on-line system identification and trajectory regeneration, and deals with unidentified failure cases. The paper develops the methodology, and concludes with numerical simulation results of representative failure cases.