Review of in-situ oxygen extraction from lunar regolith with focus on solar thermal and laser vacuum pyrolysis

In Situ Resource Utilization (ISRU) is crucial for lowering the cost of space exploration and sustaining human activity on the Moon. Multiple techniques have been studied to extract oxygen from lunar regolith, including electrochemical processes such as molten regolith electrolysis and molten salt electrolysis, as well as pyrometallurgical processes such as hydrogen and carbothermal reduction. However, one attractive technique remains underexplored, namely vacuum pyrolysis. This method utilizes high temperatures and benefits from local vacuum conditions to produce oxygen from lunar regolith composed of various minerals. Vacuum pyrolysis is particularly attractive as it is based on local lunar resources, it requires no external consumables, and it is capable to operate with any lunar soil feedstock composition. Among the possible sources of high-temperature energy, laser and concentrated solar energy are suitable options to drive the endothermal pyrolysis process on the Moon. In particular, using widely available solar energy as process heat source on the lunar surface eliminates the need for intermediate electrical production for the production of oxygen and various metallic compounds from lunar minerals. This review article compiles and examines the various works carried out on this ISRU process, and further provides different aspects to be considered for the development of an integrated and self-sufficient oxygen production process for future applications on the Moon.