Simulation and Evaluation of Throttleable LOX/LCH4 Rocket Propulsion System Architectures for In-Space Applications

Abstract

In-space missions with lunar landing stages and transfer stages require liquid rocket engines with high vacuum specific impulse and deep throttling capability. Liquid oxygen (LOX)/ liquid methane (LCH4) is a promising propellant choice for such reusable systems. This thesis studies LOX/LCH4 liquid propulsion systems in the 25 kN thrust class by comparing three candidate architectures for in-space applications. Common liquid-propellant rocket engine architectures are first assessed in a literaturebased trade-off using a weighted decision matrix and mission requirements tailored to a lander-type scenario. One open and two closed system architectures are selected: a Pressure-Fed System (PFS), an Expander Bleed Cycle (EBC) and a Fuel-Rich Staged Combustion Cycle (FRSCC). System-level models of these architectures are then implemented in EcosimPro/ESPSS, consistently sized to 25 kN for a vacuum-optimised thrust chamber, and analyzed over steady-state operating points and feasible throttle ranges using CEA-based design tools. For the FRSCC, a serial turbine arrangement with a throttle and mixture-ratio control concept is investigated. The simulations show clear trade-offs. The FRSCC attains the highest vacuum specific impulse, but at the cost of the highest chamber pressures, turbomachinery power demand and system complexity. The PFS offers a nearly comparable vacuum specific impulse with reduced thermal and mechanical loads and the simplest layout, but requires elevated tank pressures and has more restrictive throttling limits. The EBC lies in between, combining a wide throttle range and turbine exhaust gas thrusters for possible attitude control with the lowest vacuum specific impulse and highest cooling-system thermal loading. The results provide quantitative guidance for selecting throttleable LOX/LCH4 architectures for in-space missions.