Gain Scheduled FDI for a Re-Entry Vehicle

Abstract

This paper presents the design of a gain scheduled fault detection and isolation (FDI) filter for the Hopper reusable launch vehicle (RLV). The fault scenario is that of faults in the vehicle's rudder actuator and sideslip sensor during a focused 90 second period of the re- entry. Both of the considered faults strongly affect the lateral response of the vehicle, making simultaneous FDI difficult. A dynamically stable model of the Hopper RLV is considered and FDI filter design is performed on linearised models of the vehicle trimmed about the re- entry trajectory. H-infinity theory is employed for the FDI filter synthesis, with a set of LTI FDI filters designed at the trim points and then scheduled to form the gain scheduled FDI filter. The effectiveness of the LTI point-design filters and the gain-scheduled filter are determined by simulation using a tightly gain-scheduled model of the linearised vehicle's open-loop response that captures the strongly parameter varying vehicle behaviour as it tracks the re-entry trajectory. The advantages of using gain-scheduled FDI filters for FDI on RLVs are highlighted via the simulations.