Fly back booster design for Mach 5 scramjet launch

Scramjet powered accelerators have the potential to decrease the cost of space access by offering reusability as well as higher specific impulse compared to rockets. The University of Queensland Centre for Hypersonics (CfH) has developed a three stage to orbit, rocket-scramjet-rocket dedicated small payload (100-200kg) launcher concept for LEO and SSO called SPARTAN. Due to the restricted operational envelope of scramjet engines, a rocket first stage remains necessary for scramjet ignition at Mach 5. Therefore, a fly back rocket booster (FBB) concept has been developed for integration with SPARTAN. The goal of this study is to investigate the feasibility of utilising a pivot wing, reusable FBB to enable scramjet launch by conducting conceptual design and trajectory analysis. The FBB accelerates the launch stack to Mach 5 and 26 km altitude before staging and scramjet ignition. After separation, a re-entry aero-braking manoeuvre is performed. Wings and propellers are deployed when the FBB decelerates to Mach 0.2. The FBB then performs a coordinated turn and flies back to the launch site. Conceptual design has been performed by concurrently assessing requirements related to ascent, re-entry and fly back. This includes systems packaging, gravimetrics, flight dynamics, propulsion and aerodynamics. Pseudo-spectral optimal control is used to calculate the stack ascent trajectory. Pseudo 5Dof trajectories with an acceleration autopilot are used to model the re-entry while 3DOF trajectories are used to model the fly back. Results show successful scramjet launch conditions and return trajectory of the FBB, demonstrating the feasibility of the system.