Hydrogen reduction of lunar samples in a static system for a water production demonstration on the Moon

Abstract

In situ resource utilisation (ISRU) refers to the extraction and use of local materials, and numerous ISRU techniques have been proposed for use on the Moon. Hydrogen reduction of iron oxide-bearing minerals in the lunar regolith, such as ilmenite, has long been suggested as a potential method for producing water on the Moon to support exploration. Generally, reduction of lunar regolith has been proposed and tested in gas-flowing systems which utilise pumps to re-circulate gases (herein described as dynamic systems), and have been trialled in terrestrial laboratory and simulated environments. However, such technologies have yet to be validated on the lunar surface. An alternative to the dynamic reactor is a static system which utilises a cold finger to condense water from the vapour phase, negating the need for a more complex system where gases are continuously pumped away. The PROSPECT Sample Processing and Analysis (ProSPA) instrument is one such static system that is to be used to measure volatiles in the lunar regolith as a payload onboard the Luna-27 lander. Previous work using a breadboard model of ProSPA led to the development and optimisation of a procedure for extracting water from ilmenite. The present work describes the application of these procedures to the reduction of a lunar simulant (NU-LHT-2M), a lunar meteorite (NWA 12592), and two Apollo soils (10084 and 60500). Three 45 ​mg samples of each material type were reacted in a furnace at 1000 ​°C for 4 ​h in the presence of approximately 420 ​mbar of hydrogen. All samples reduced to some extent, with the Apollo mare soil (10084) producing the highest average yield of 0.94 ​wt % O2; this compares favourably to the yields of ~3–4 ​wt % O2 by other more optimised demonstrations of O2 extraction from Apollo soils. Samples with higher ilmenite content produced higher yields, however, pyroxene and olivine within the samples also showed some minor reduction. The results demonstrate that a static system such as ProSPA is capable of reducing lunar regolith of various compositions and producing measurable yields of water. The technique is therefore appropriate for performing in situ resource utilisation experiments at the lunar surface. The simple and small scale technique is also appropriate for use in evaluating the grade of potential feedstock for the production of water by hydrogen reduction on the lunar surface.