Ramjet-powered reusable launch vehicle control by sliding modes

One possible approach to pitch control of an air-breathing reusable launch vehicle is differential throttling of opposite engines mounted on the conical lifting body. The vehicle must operate over a large range of flight regimes. The problem is aggravated by the relatively large angle of attack, which produces nonsymmetrical engine operation. The dynamics of controlling supersonic compression inlets also requires very rapid response times. A pitch controller architecture is proposed based on the sliding mode control (SMC) approach. SMC is a robust, nonlinear control technique characterized by its total insensitivity to matched disturbances and its perfect rejection of unmatched disturbances. The pitch control of a conical reusable launch vehicle by opposite engines operating in ramjet mode is simulated. In response to pitch induced disturbances, the SMC controller accurately tracks the prescribed nominal moment through generation of required engine thrust profiles, The control occurs in a minimum settling time with no chatter.