Conceptual Study on Low-Melting-Point Thermoplastic Fuel/Nitrous Oxide Hybrid Rockoon

A hybrid rockoon, which is a hybrid rocket launched from a high-altitude balloon, is proposed. The rocket system configuration was studied for single-stage or multiple-stage rockets, and the performance and range safety requirements were considered. The propellants of the hybrid-rocket motor are a low-melting-point thermoplastic fuel and nitrous oxide, which are beneficial, owing to their mechanical properties at cold temperatures experienced in high-altitude environments. Three-dimensional launch trajectory analyses were performed for science missions aimed at sampling cosmic dust levitating in the upper stratosphere. The apogee altitude can be significantly increased by elevating the altitude of the launch point because the problem of low thrust level of the hybrid rocket is solved by increasing the nozzle expansion ratio. Suborbital trajectories with multiple apogee points and orbital missions to extremely low Earth orbits are presented, which provide a long flight path in the upper atmosphere. The sequence of events and flight characteristics of the proposed hybrid rockoon system are discussed, and necessary technological improvements in the structure and propulsion systems are presented.