Alternative geometry hybrid rockets for spacecraft orbit transfer

The cost-effectives mall spacecrafht as becomea n enablingt ool in the pursuit of near earth space commerce. Although small spacecraft have typically forgone the complexity and historically high cost of spacecraft propulsion, the inability to cost-effectively reach specific data gathering orbits from secondary launches presents a serious limitation to the small spacecraft industry. A cost-effective propulsion system capable of moving the secondary spacecraft from the launch orbit to the required mission orbit will effectively increase the number of viable secondary launch opportunities and in some cases provide a higher scientific or commercial return. Propulsion will also allow the dispersing of multiple spacecraft from a single launch vehicle and the inherent ability to de-orbit after a useful mission life. While other propulsion alternatives were considered in this research program, the hybrid rocket was identified as having high potential for suiting the established high-performance, lowcost and safety criteria. However, as this research has shown, the conventional hybrid rocket is not well suited to incorporation within small spacecraft; this is primarily due to the required length verses diameter (UD) to achieve high performance in the conventional hybrid. This research program has produced and tested a novel hybrid rocket engine. The all-new engine is significantly different from the conventional hybrid, exhibiting higher performance and with a geometry that drastically reduces hybrid rocket integration and operation issues. In addition, the new hybrid design has been successfully tested at higher volumetric loading factors than the conventionadl esignsi dentifiedi n the literature. The new alternative geometry hybrid rocket employs tangential oxidiser injectors that induce a vortex flow field to the centrally mounted rocket nozzle. The induced flow field has been shown to provide better fuel and oxidiser mixing. In addition, the tangential oxidiser injection provides an inherent film cooling effect for the combustion chamber wall, allowing the chamber to be fabricated of low cost materials. The new hybrid rocket engine was dubbed the Vortex Flow "Pancake" hybrid or "VFP". This researchp rogramr epresentsth e most technologicallya mbitiousp ropulsionr esearch program conducted by the Surrey Space Centre to date as the tools to analyse and design this engine had to be experimentally derived. Although the fundamental process of burning solid fuel remains unchanged, the combustion chamber gas-dynamics - so vital for predicting fuel liberation and performance within the conventional hybrid - are radically changed in the new configuration. Whereas the conventional hybrid has demonstrated a strong correlation with increasing combustion port diameter and fuel liberation, this research has shown that fuel liberation within the VFP does not obey any such relationships. Operationally, this research has shown that the VFP exhibits a higher fuel volumetric loading factor, higher combustion efficiency and less of an O/F (and consequent performance) shift than conventional designs. This research has proven the VFP to be superior to the conventional hybrid design in every aspect tested. However, this is only part of the benefit realised by the new VFP design as the external geometry of the VFP is the primary benefit enabling the technology to be applied to small spacecraft. Conventional hybrids need L/D ratios in excess of 15 to provide adequate performance, the novel VFP design has been regularly tested at UD's less than 1 with combustion efficiency very near 100%. This unique hybrid characteristic allows the VFP to be integrated on the outside of a spacecraft, in or as part of the spacecraft separation system. An externally mounted engine conserves centrally located spacecraft volume (reducing the need for multiple oxidiser tank scenarios). In addition, the external mount also allows waste heat to be radiated to space rather than other (internal) spacecraft components.