Investigation and development of regolith excavation and handling mechanisms for lunar in-situ resource utilisation

UoM administered thesis: Phd

Abstract

In recent years, space agencies and, for the first time, private companies, have invested heavily in lunar exploration. This comes as no surprise, as numerous scientific questions remain unanswered, and the Moon is considered a testbed for technology necessary to eventually land humans on Mars. To make exploration of the Moon for extended periods of time feasible and more sustainable, the use of lunar resources, termed in situ resource utilisation (ISRU), will be crucial. The most abundant resource available on the lunar surface is the lunar soil or regolith, as it bears minerals, useful elements, or water ice. A multitude of technologies to process regolith have been proposed and tested terrestrially with regolith simulants to date. Despite these developments, two critical steps of the ISRU process chain, namely the excavation and handling of the feedstock material, are often oversimplified or forgotten. The presented work, therefore, aims to advance the current state of knowledge regarding excavation and handling methods suitable for the harsh lunar environment, identify current knowledge gaps, and develop technology to simplify the ISRU process chain. Accordingly, an extensive review of existing lunar regolith excavation techniques and technology demonstrators is presented, which aims to compare each system based on a number of parameters (Chapter 3). However, it is concluded that comparisons are almost impossible due to the different and often incomplete reporting of operational characteristics of excavation equipment. Thus, recommendations are made for the uniform reporting of future regolith excavation experiments. Any experimental investigation of regolith excavation and handling mechanisms requires regolith simulants to perform laboratory work. These are often not available in sufficient quantities for large-scale testbeds and their high cost restricts such setups further. Therefore, readily available and low-fidelity analogue materials that possess similar geotechnical properties to regolith are necessary. Two such materials are identified herein, and a full geotechnical characterisation is performed to make laboratory excavation experiments comparable (Chapter 5). The results show that the two analogue materials, named UoM-B and UoM-W, are well suited for the use in engineering experiments and have since become available to the wider ISRU community. Since the reduction of excavation forces is crucial for the viability of regolith extraction by small robotic vehicles and to maximise their capabilities while minimising launch mass, a study of four different leading-edge geometries and three operating parameters is performed. Horizontal and vertical excavation forces are recorded and the use of vibrations to reduce such forces is investigated as a proof-of-concept (Chapter 6). The most beneficial operating conditions are identified and, critically, it is shown that vibrations lead to force reductions of up to 50 %. Based on the laboratory results, the development and test of a small excavation device for use with a lunar rover currently under development by an industrial partner is presented (Chapter 7). A novel mechanism was developed in the presented work that combines regolith excavation and size separation in one system and is, therefore, capable of delivering two distinct size fractions to ISRU processes down the process chain. This capability eliminates an intermediate regolith transportation step between excavation and beneficiation, reducing process complexity while increasing robustness. Laboratory tests confirm that up to 100 g of soil can be excavated in a single scoop with excavation forces below 8 N (40 % of the traction force provided by the rover under lunar conditions) and a system mass less than 2 kg. The mechanism utilises vibration to size separate regolith; to assess a sensible level of size separation, an experimental study of gravitational dry sieving of different regolith simulants/analogues is presented. Results show that the residence time scales with a power law and that the aperture size must be chosen diligently. Lastly, a brief experimental study of suitable leading-edge materials for the mechanism is conducted with a test stand that simulates the real-world deployment conditions. It is shown that wear of the cutting implements is not of major concern for small-scale excavators operating at very low excavation forces and, thus, low contact pressures.

Details

Original languageEnglish
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Award date31 Dec 2021