Simulation for Roton, a Recoverable Spacecraft with Tip Rocket Rotor

This paper describes the requirements, development, testing, and validation of a hardware-in-the-loop simulator for a recoverable spacecraft, Roton. Roton is a piloted, Single Stage to Orbit (SSTO) spacecraft that uses a rotor with tip rockets for final descent and landing. The simulation of Roton had three primary objectives. The first objective was to predict the performance of the vehicle during final decent and landing. The second was to evaluate the handling qualities and the third was to perform pilot training prior to actual flights. The simulation model was based on the primary components of the vehicle. The fuselage was simulated by a 6 degree of freedom rigid body mass and the rotor was simulated using a blade element approach. The directional control device consists of three small rockets on a controllable hinge mounted on the fuselage behind the crew cabin. Simple equations were used to model the tip rockets as well as for the direction control rockets. The control system was a simple linkage system from pilot sticks to the swashplate and from the pedals to the directional control device. A simple rotor speed feedback was used to control the fuel flow to the tip rockets and in turn control the rotor RPM. Non-real time analysis was performed to evaluate the performance and flying qualities of the vehicle. A real time simulation with actual hardware in the loop was utilized for pilot training. Simulation results showed good agreement with the three available flight test results. The real time simulation with the pilot-in-loop validated the choice of fidelity for various subsystems.