Controlling a launch vehicle at exoatmospheric flight conditions via adaptive control allocation

Abstract

The focus of this paper is the control of a reusable launch vehicle at exoatmospheric flight conditions, in the presence of actuator effectiveness uncertainty. Since during exoatmospheric flight, dynamic pressure is nonexistent, aerodynamic control surfaces cannot be used. Under these conditions, reaction control jet actuators can provide the necessary thrust to control the vehicle. Reaction control jets have only 2 states, namely, on and off, and continuous control inputs can be implemented with the help of pulse width modulation, which is also employed in this paper. A continuous controller is designed in the outer loop and a control allocator is used to distribute the total control input among redundant actuators, whose effectiveness are assumed to be unknown. The unknown actuator effectiveness is addressed with the help of an adaptive control allocator. A representative model of a reusable launch vehicle equipped with reaction control jets is used to demonstrate the effectiveness of the overall control scheme.