Abstract
Introduction: The availability of energy on the Moon is a constraining factor in lunar ISRU for constructing a lunar habitat and producing water. Microwave energy has been shown as an efficient method of volumetrically heating mare lunar simu-lant to the melting point [1,2] for use in habitat construction. There are many techniques for extracting oxygen from lunar simulants, of which hydrogen reduction of ilmenite-rich regolith is a favourite. It requires a relatively low temperature of ~900 ºC and is comparatively simple, and as a result it has been demonstrated to the highest TRL 5 [3]. However, it is limited to ilmenite-rich samples and has a low oxygen yield. In this study, we investigate the possibility of combining the microwave heating of simulants for construction purposes and simultaneously extracting oxygen from lunar simulants. The rate of the hydrogen reaction is increased by higher temperatures [4]. However, the reaction rate decreases as hydrogen must diffuse into the bulk sample while water diffuses out. Method: Experiments were conducted on 50g samples of simulant placed in a vacuum microwave chamber [5]. JSC-1A simulant was selected as it represents a low titanium lunar mare regolith and has been used in previous microwave experiments. Il-menite was added to give a range of simulants with 0 to 20 wt.% ilmenite. The microwave cavity was evacuated and flushed several times until a vacuum pressure below 1x10-3 mbar was attained; it was then filled with ~0.2 bar hydrogen. The sample was heated by 1000 W microwaves for an hour. The gas composition in the chamber was sampled by a quad-rupole mass spectrometer every 30 seconds with a mass range from 1 to 100 amu. A cold trap in liquid nitrogen was used to collect water. The gas pressure and composition, sample surface temperature, and sample appearance were monitored throughout the heating. At the end of the microwave heating, the excess gas was evacuated through the cold trap. The cold trap was then heated to 100 ºC and the released water vapour was trapped by liquid nitrogen onto a smaller cold finger. The amount of water produced was determined by weighing the cold finger before being transferred by pipette to a 2 mL vial. Blanks were determined by repeating the experiment with helium instead of hydrogen and by conducting an experiment without a sample. Results: A typical result for the gas composition during microwave heating is shown in Figure 1. Initially, the hydrogen intensity and gas pressure