Upper stage rocket guidance and control using discontinuous reaction control thrusters via sliding modes

In spring 1995 a very significant academic project took place at the University of Alabama in Huntsville. This integrated project supported by NASA Marshal Flight Center and major aerospace, companies aimed at designing the MSLS upper stage, based on an hybrid rocket design. This project included the design of the avionics system, and of the guidance and control subsystem (G&C). This paper presents the architecture of the G&C, and the design of corresponding algorithms. Given the discontinuous nature of the attitude thrusters used in the reaction control system, the proposed design is based on the output tracking sliding mode technique. The proposed implementation of the design replaces the traditional high frequency relay switching by a so called smoothing sliding mode controller. It uses a saturation law, where the amplitude of the control modulates the duration of thruster´s pulses