Fault diagnosis schemes for atmospheric Re-entry Vehicles actuators: Comparison of two approahes

This paper deals with the design of robust model-based Fault Detection and Isolation (FDI) schemes for atmospheric Re-entry Launch Vehicles (RLV). Two FDI schemes involving residual generators are applied to the HL-20 RLV, and compared to each other. The first method is based on unknown input observers (UIO) and the second one involves H_∞/H_- filters. A key feature of the approaches with regards to other model-based FDI schemes reported in the literature, is that the coupling between the in-plane and out-of-plane vehicle motions, as well as the effects that faults could have on the GNC (Guidance, Navigation and Control) performance are explicitly taken into account within the design procedure. To compare the fault sensitivity and robustness performance of the two FDI schemes, the general FDI-oriented μg performance measure developed by (Henry and Zolghadri, 2005a), is proposed. Both the μg validation test and nonlinear simulations from a ”medium-fidelity” simulator, demonstrate that the UIO and the H_∞/H_- based FDI units could be considered as a viable candidate for onboard FDI algorithms for RLVs.