Abstract
The goal of the research was to investigate a low cost bi-propellant engine of 40N thrust, suitable for integration into a small spacecraft. Small spacecraft are often launched as secondary payloads, where the primary spacecraft dictates the orbit. Thus propulsion is fast becoming a necessity to change the initial orbit into the mission-required orbit. The low-cost driver forced the use of non-toxic or 'green' propellants and the imposed volume constraints drove the requirement for a high density Isp. The propellant combination chosen was kerosene and hydrogen peroxide (HTP), both readily available and cheap liquids. Unfortunately HTP suffers from the intrinsic decomposition into oxygen and water during storage, which in a sealed tank causes the pressure to rise until rupture occurs. The compatibility of fluoropolymer and aluminium tank liner materials was measured through decomposition rate determination, chemical analysis and mechanical pull tests. The results demonstrated that while pure aluminium is superior to the fluoropolymer FEP, the latter has the ability to passively vent oxygen. This enabled a passively vented tank to be produced, which demonstrated sealed storage over 18 days. In order to maintain the low cost approach, high temperature alloys for the thruster were avoided. A range of cooling options were considered, however for the purpose of maximising the density Isp and minimising the complexity of the engineering, the novel decomposed HTP cooling system was chosen. The theory was evaluated with five practical engines built and tested. Combustion experiments determined the ignition conditions, combustion efficiency and stability. Cooling experiments were executed to determine the effectiveness of nitrogen and decomposed hydrogen peroxide coolant for the chamber and nozzle of the engine. The test data showed that this form of cooling is effective and a density Isp performance comparable to a commercial hypergolic bipropellant engine is possible.