Control Allocation of Reaction Control Jets and Aerodynamic Surfaces for Entry Vehicles

A linear programming approach to mixing continuous and pulsed control effectors is proposed. The method is aimed at applications involving reentry vehicles that are transitioning from exoatmospheric flight to endoatmospheric flight. In this flight phase, aerodynamic surfaces are weak and easily saturated and vehicles typically rely on pulsed reaction control jets for attitude control. Control laws for these jets are typically developed using single-axis phase plane analysis which has proven to be sufficient for many applications where multi-axis coupling is insignificant and when failures have not been encountered. Here we propose using linear programming techniques to blend continuous control effectors and pulsed jets in order to generate moments commanded by linear or nonlinear control laws. When coupled with fault detection and isolation logic, the control effectors can be reconfigured in order to minimize the impact of control effector failures or damage. When the continuous effectors can provide the desired moments, standard linear programming methods can be used to mix the effectors; however, when the pulsed effectors must be used to augment the aerodynamic surfaces, mixed integer linear programming techniques are used to determine the best combination of jets to fire. The reaction jet control allocator acts as a non-uniform quantizer that generates applied moments that approximate the desired moments generated by a continuous control law. Lyapunov theory was applied to develop a method for determining the region of attraction associated with a quantized vehicle attitude control system.