Adaptive guidance and control for autonomous launch vehicles

Adaptive guidance technology is developed to expand the potential of adaptive control when applied to autonomous launch systems. Specifically, the technique of pseudo-control hedging is applied to implement a fully integrated approach to direct adaptive guidance and control. For rocket powered launch vehicles, a recoverable failure will generally lead to a reduction in total control authority. Pseudo-control hedging was developed to prevent the adaptive law from 'seeing' and adapting to select vehicle input characteristics such as actuator position limits, actuator rate limits and linear input dynamics. In this work, a previously developed adaptive inner-loop provides fault tolerance using an inverting control system design augmented with a neural network. An adaptive outer-loop 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. The paper develops the methodology for adaptive trajectory following and control. Numerical simulation results in representative failure scenarios for the X-33 reusable launch vehicle demonstrator are then presented. The paper concludes with a brief summary of an autonomous guidance and control system appropriate for future reusable launch vehicles, and the application of the developed adaptive components within such an architecture.