WITHDRAWN: Lunar ISRU Metal-Fueled Hybrid Rocket Propulsion: Ignition, Combustion Dynamics, Performance Analysis, and Experimental Demonstration

This study presents the development and experimental evaluation of a fully metal-based hybrid rocket propulsion system designed for in-situ resource utilization (ISRU) on the lunar surface. Magnesium (Mg) and aluminum (Al), both abundant in lunar regolith, were processed into hybrid fuel grains using sodium silicate as a ceramic-type binder. Thermochemical analysis with NASA CEA was used to select mixture ratios and operating conditions, highlighting the need to exceed metal-oxide vaporization temperatures to avoid excessive slag formation and to sustain chamber pressurization. Laboratory-scale hybrid motor tests were performed to characterize ignition behavior, regression rate, thermal response, and combustion stability under gaseousoxygen operation. Among the tested formulations, the composition containing 71% Mg, 19% Al, and 10% binder demonstrated robust ignition, stable melt-layer formation, reduced nozzle deposition, and a vacuum specific impulse approaching 350 s at very low O/F ratios. Measured regression rates in the order of 1.3–1.6 mm/s at oxidizer mass fluxes of 4–5 kg/m2·s confirm that metal-fueled hybrids can operate in a high-regression regime comparable to or exceeding classical liquefying hybrids. These results indicate that Mg–Al hybrid propellants can deliver high performance while substantially reducing lunar oxygen production requirements. The demonstrated stability, manufacturability from powder-based processes, and ISRU compatibility position metal-fueled hybrid engines as a promising propulsion option for lunar ascent, cargo transport, and surface-to-orbit missions within future Lunar architectures.