Design of a N20/HTPB Hybrid Rocket Motor Utilizing a Toroidal Aerospike Nozzle

Abstract

Current efforts by the student members of the sole student rocket group at Arizona State University, Daedalus Astronautics, have been focused on development of both a hybrid rocket motor and an aerospike nozzle. Hybrid rocket propulsion has combined properties of both solid and liquid rockets giving it advantages over the individual systems. This is a concept which has gained a more substantial footing with the success of Scaled Composites and SpaceShipOne. Daedalus Astronautics has designed and developed a simple hybrid rocket motor for the use in their high-powered sounding rocket program. The designed motor utilizes nitrous oxide and hydroxyl-terminated polybutadiene (HTPB) for oxidizer and fuel respectively. The key components of the hybrid design and analysis include the oxidizer solenoid valve, injector, pre-combustion chamber, fuel grain, post combustion chamber and nozzle. Initial testing of the hybrid rocket motor have been conducted utilizing a standard “bell” nozzle in order to allow for direct comparison to a more advanced nozzle design. A toroidal aerospike nozzle with an isentropic contour was designed and implemented for use with the hybrid due to its advantages over the standard and widely used “bell” shaped nozzle. An aerospike nozzle has the ability to perfectly expand the exhaust gas at all altitudes increasing the performance of the system. This design includes the use of graphite inserts at the nozzle throat to deter erosion and expansion which has been problems in previous designs. By integrating this nozzle with the hybrid rocket motor a high performance launch system can be achieved.