Optimal Design of Hybrid Rocket Small Satellite Launchers: Ground Versus Airborne Launch

A three-stage hybrid rocket is considered as a small satellite launcher. The same engine is used in different numbers in each stage: six, three, and one in the first, second, and third stages, respectively. This design choice aims at an overall reduction of the launcher cost. The propellants are liquid oxygen and a paraffin-based fuel. The performance of different feed systems and launch options are evaluated: the feasibility of a ground launch is analyzed and compared to similar three-stage launchers with airborne launch using both a gas pressurized feed system and an electric turbopump feed system. The optimization procedure exploits a direct method to evaluate the best values of engine design parameters, whereas an indirect method optimizes the ascent trajectory once the engine design is given. Constant power and blowdown operation are, respectively, assumed for the electrical feed system and the gas pressurized feed system. The initial mass of the launcher is given (5000 kg), and the payload mass is maximized for a given insertion orbit. The initial thrust is fixed in order to have an initial acceleration equal to 1.4g. The nozzle expansion ratio in the first-stage engines is reduced to avoid separation at liftoff in the ground case, and the third-stage engines are used at a lower vacuum thrust level to satisfy maximum acceleration constraints. The results show that the proposed small satellite launcher concepts are able to deliver payload masses in the range of 40-100 kg into the desired orbit.