Unified GN&C system for the Space Rapid Transit launch vehicle

This paper presents the overall design of a guidance, navigation and control system for a novel two-stage to orbit launch vehicle. The Space Rapid Transit, or SRT, is being designed by Princeton Satellite Systems to address the most critical needs of the United States space program: namely the rapid, safe and economic delivery of payloads and astronauts into low Earth orbit. The launch of the vehicle progresses through four phases: 1) atmospheric flight with the aid of a ferry stage, 2) a boost phase to LEO, 3) orbit acquisition and rendezvous, and finally 4) reentry and gliding landing. In order to achieve accurate orbit insertion, the ferry stage must first deliver the orbiter to a precise position and velocity at the correct time. Non-linear dynamic inversion techniques are used to design a guidance law for the powered flight phase. The boost phase uses a gimbaled main engine with classical feedback control to zero the disturbance torque. Once in orbit, the reaction control system utilizes 16 thrusters to perform attitude maneuvers and small orbit maneuvers for rendezvous. Relative orbit guidance is then performed by formulating a robust linear program that plans minimum-fuel maneuvers to achieve target states subject to avoidance constraints and initial state uncertainty. Another linear program is used with weighted slack variables to allocate pulsewidths to the thrusters so that the force and torque demands for orbit and attitude control are achieved as closely as possible, subject to the maximum thrust constraints. The overall design of the guidance and control systems for all flight phases is presented along with preliminary simulation results.