Detailed Design Study of an Electric Hybrid Power Pack for LOX and CH4

Abstract

When it comes to the transport of liquids or gases in chemical rocket propulsion engines there are several options. The most high-power engines use turbopump feed systems with liquid propellants. These can be divided in several sub cycles. Subject of this master thesis is a fusion of the expander and the electric pump cycle, the so-called Electrically Augmented Expander Cycle. This cycle has a heat exchanger system around the thrust chamber, a turbine that runs with the expanded gas at the higher throttle range, and an electrical pump that powers the motor during start-up and lower throttle. Two sub-cycles are investigated, namely an open and a closed cycle. The open cycle expels a small fraction of the fuel stream after powering the turbine, whereas the closed cycle directs all of the fuel into the combustion chamber. Considering previously performed analyses, CH4/LOX is used as a propellant combination for the thruster since it offers advantages for the envisioned missions to the Moon or Mars. The engine developed in this study should be capable of multiple restarts to facilitate various mission profiles. Additionally, it must be throttleable down to 30% of its rated power level of 30 kN, enhancing maneuverability and efficiency in different flight phases. The design process begins with the establishment of boundary conditions, including parameters such as the chamber pressure, the oxidizer to fuel ratio and the tank pressures. Several aspects are taken into account, like the heat deterioration of methane when passing its supercritical temperature in the cooling channels. These conditions set the framework within which the engine must operate. An iterative development loop is then employed to refine the design. Through successive iterations, the study adjusts key parameters and integrates feedback to adapt and optimize subsystem performance. Special focus is laid upon the power pack design of the engine. The results of the computational analysis are benchmarked against data from existing rocket engines, like the RL10A-3-3A engine, to validate the theoretical models. The findings highlight the advantages and limitations of both cycles. At the end of the thesis, a conclusion is drawn on the results of this work and an outlook for the future and possible suggestions for improvement are given.