Guidance and Control System for Lifting-Body Flight Experiment : System Evaluation and Flight Control Parameter Optimization

The lifting-body shaped vehicle has been studied as the candidate for a future re-entry vehicle. Because of a wingless structure, there are several advantages, such as structural stiffness against atmospheric heating, greater payload capacity, and suitable shape stored in a rocket fairing. Furthermore, since it flies utilizing aerodynamic force, the vehicle motion can be controlled more flexible compared to a capsule-type re-entry vehicle. However, the controllability is inferior to a normal aircraft and flight control becomes difficult at low air speed because of a low lift-drag ratio. Especially in approach and landing phase, accurate flight control is required while the air speed is quite low. To establish landing technology for a lifting-body flight vehicle, LIfting-body FLight EXperiment (LIFLEX) had been planned. In this experiment, the key technology to be developed is a flight control system. The experimental vehicle has to meet given specifications and land on a run-way against various uncertain conditions such as environmental uncertainties and vehicle model errors which are expected to exist in the real world. This paper describes an overview of the control system design for LIFLEX, and system evaluation by a numerical flight simulation. First, the system performance and robustness is evaluated incorporating those uncertain parameters. Then, the control design parameters with the non-linear system are directly optimized to maximize a probability of mission achievement. Finally, uncertain parameters, which are inherent for the LIFLEX vehicle, are revised for more general flight system, and the revised system is evaluated to confirm its robustness as additional information for the development of a future re-entry vehicle.