Trade-off and optimization for a thermal lunar water extractor

Abstract

Water is an essential resource for space exploration, for both robotic and human exploration. In the future, these resources can be used to produce rocket propellant. This Space Resource Utilisation (SRU) would reduce the cost of spacefaring significantly. Especially considering the current development of multiple commercial lunar landers, the lunar economy will soon become more accessible, which further drives the need for water extraction equipment. Multiple methods to thermally extract and capture water from lunar regolith (e.g. in-situ thermal extraction, excavation and reaction chamber) are already envisioned, and this research aims to select the most promising concept based on the optimization of parameters. The first step will be to design a set of different concepts which can be compared to each other. Both a quantitative as well as a qualitative trade-off will be performed, since the fidelity of the designs is likely not enough information to accurately compare them to each other by quantitative measures alone. Also, factors like complexity are hard to define in numbers, but should not be excluded in a selection. For the preliminary design, the surface coverage of heating elements in the system, the water ice content of the regolith in wt.% as well as the power available to the system are investigated in a parametric study. Alternatively, the power could be an output of the design rather than the input, and the power is dependent on the amount of energy required to sublimate the accessible water. Multiple criteria will be taken into account to perform the comparison of the extraction methods, the most relevant consisting of: 1) The accessibility of the water extractor to the water ice. The ability to heat water-ice to the sublimation temperature at sub-surface depth. 2) The time and energy required to get a certain yield. A sensitivity analysis can be performed on the time factor and the concept of operations to find an optimal scenario. 3) The complexity and the added failure modes, increased risks, and potential losses. This work is embedded in the research group Synergetic Material Utilisation (SMU) at the German Aerospace Center (DLR).