Theoretical and experimental methods for lunar regolith / rock related mechanical issues in lunar minerals mining

The moon possesses rich mineral resources,for example,titanium,thorium,uranium and thorium,as well as some rare minerals such as pyroxferroite and zircon that do not exist on the earth. The exploitation and utilization of those resources can effectively solve the current global issues of resource depletion and environmental damage,which has become the focus of the new round of global space exploitation competition. However,the special gravity,vacuum and temperature environment on the moon,together with the distinctive composition,structure and geometric character- istics of geological materials result in the individual mechanical behaviour and engineering response of lunar regolith and rock,which bring a series of unprecedented challenges on both lunar mining and base construction. In terms of space environment,the gravity on the moon is only 1 / 6 of that on the earth,the vacuum on the lunar surface exceeds 1． 01×10-12 kPa,the highest temperature is up to 130 ℃,the lowest is -183 ℃,and the temperature difference is as high as 313 ℃ . As for the lunar geological materials,the particle shape of lunar regolith processes typical porous and multi-hook geometric characteristic. The lunar regolith also has a very large particle size variation,and exhibits a typi- cal regolith / rock mixed structure characteristic because of the existing of large lunar rock bulk. Both the lunar regolith and rock demonstrate significant titanium-rich and iron-rich composition characteristics. Therefore,the systematic un- derstanding of the above factors induced mechanical behaviours of lunar regolith and rock is the premise for the safe and efficient lunar mining. Those mechanical issues include the behaviour of lunar regolith / rock under lunar gravity induced low stress level and low stress gradient,the behaviour of lunar regolith / rock under lunar ultra-high vacuum and extreme temperature environments,the behaviour of lunar regolith related to abnormal particle shape,and the be- haviour of lunar regolith / rock related to the distinctive composition and structure characteristics. Therefore,several the- oretical and experimental innovative research methods need to be put forward,which can effectively make up for the incapability and shortcoming of current research methods. In theoretical aspects,the stress gradient-related high-order mechanical theory for lunar regolith / rock needs to be proposed to characterize the behaviour of lunar regolith / rock un- der gravity induced low stress gradient. The mathematical representation and numerical reconstruction of lunar regolith particle is another theoretical innovation,which may help to reveal the complex particle shape of lunar regolith and its influence on mechanical properties. Furthermore,the abnormal particle shape-related multiscale mechanical theory for lunar regolith should be developed to build the connection between its microscopic particle shape and macroscopic me- chanical behaviour. In the experimental aspect,both the terrestrial experimental techniques used to simulate the lunar space environment and used to prepare lunar regolith / rock simulants need to be carried out,which can provide a basic experimental platform for lunar mining related mechanical issues.