Hypersonic Vehicle for Space Access Using Hydrocarbon Fuel

Current rocket technology is extremely efficient, and operates close to theoretical limits. Recent advancements in technology have contributed to a boom in the small satellite industry, which has left many operators without access to affordable launch systems. In order to increase the efficiency and reduce the cost of small satellite launches, new propulsion methods must be investigated. The University of Queensland's Centre for Hypersonics has been developing a three-stage access to space system, with the hydrogen-fueled scramjet-propelled second stage named the SPARTAN (Scramjet Powered Accelerator for Reusable Technology Advancement). The system has been designed as a cost-competitive alternative to rockets for the launch of small satellites of approximately 150kg to low earth orbit (LEO). Scramjets have a higher specific impulse than rockets, and scramjet-powered vehicles utilize aircraft-like design which allows them to be reusable - something which is proving to be an important factor within the space industry. Hydrogen has long been the favored propellant for SPARTAN, due to its high specific energy and ignition properties, though it suffers from a low energy density. The hydrocarbon ethylene has over three times the energy density of hydrogen, which allows for a reduction in the volume of propellant carried aboard the vehicle. In turn, the vehicle may be smaller, reducing manufacturing costs and thus increasing the viability of the overall concept. This project aimed to determine the effects of switching SPARTAN to ethylene operation, in terms of the overall geometry and payload size which can be carried to LEO. A high-fidelity computer aided design (CAD) model of SPARTAN has been produced, which determines the overall mass of SPARTAN and its propellant, and the location of its center of gravity (CG), at any given geometric parameters. The model was used to generate a mass database for an array of different vehicle configurations. This database was fed into the in-house trajectory simulation software, Stalker, which determines the maximum payload size a given configuration can carry to orbit. Dakota, an open source optimization software, was used to drive Stalker and evaluate the performance of a wide variety of vehicle configurations in order to determine the optimum solution. The result is a configuration which can carry 156.60kg of payload to LEO, with a SPARTAN and third stage total mass of 9069.00kg. The vehicle is able to reach a final Mach number of 8.85 before running out of propellant, and launching the third stage rocket. This proves that ethylene is capable of propelling a scramjet vehicle to high-Mach flight. However, the vehicle is unable to match the performance of the existing hydrogen design, which is predicted to carry 219.30kg to LEO with a total mass of 8735.00kg, and a final Mach of 9.50. Based on these results, the study concludes that ethylene is not worth additional pursuit for SPARTAN's operation.