Thermal Conductivity Measurements of Dry and Icy Lunar Regolith Simulants
Creators: name: Wache, Henning
Publisher: name: Zenodo
Year: 2024

description: Now, more than ever, humans have longed to explore outer space. Recent advancements in bothtechnology and science have brought us closer to establishing a permanent human presence beyond our home planet. The Moon represents a pivotal point in humanity’s exploration of thesolar system. However, a permanent human presence outside the reach of Earth requires not onlyvast amounts of fuel but also consumables for the crew, which cannot be sourced from our homeplanet indefinitely. With the recent confirmations of the presence of water ice on the lunar surface,such long-term objectives begin to appear within reach. If extracted, this water could not only beused to support human life, but also to be transformed into hydrogen and oxygen, which yields apotent rocket propellant that might help transport humans to Mars and beyond.One question that is still unanswered to date is the exact location and morphology of this ice onthe initially thought dry lunar surface. Since the Moon has no significant atmosphere, water canonly exist in extremely cold regions. Fortunately, the lunar south pole contains some of the coldest places found in the entire solar system, the so-called Permanently Shadowed Regions (PSRs),which are craters where the sun never shines. Beyond the boundaries of these craters, the roughand weathered surface, composed of a highly irregular and porous material called regolith, couldprovide thermal insulation from what lies below, possibly allowing the presence of solid water ice.In order to physically model local temperature conditions in ice-bearing regions on the lunarsurface, thermal conductivity measurements are required as input parameters. Since in-situ orremote-sensing missions are very costly, this study aims to provide laboratory measurements of thethermal conductivity of icy regolith simulant materials, which can be used as an approximationfor the thermal conductivity of real lunar icy materials. As the nature of ice in such a materialalters the thermal properties, this study focuses on a specially created discrete microgranular icyregolith simulant and compares it to a fused icy mudpie simulant to provide insight into twopossible ice morphologies that might occur on the Moon. The novel microgranular simulant aimsto simulate the impact that millennia of space weathering may have had on the ice present on thelunar surface, while the mudpie simulant resembles fused subsurface ice layers.The objective of this study is to analyze the temperature behavior of the thermal conductivity ofsuch icy samples in comparison to dry regolith simulant samples. The effects of ice content butalso temperature-dependent effects such as sintering and possible re-cementation processes viasublimation and deposition are of interest, given that diurnal temperature changes on the Moonmost likely influence any ice in the upper surface layers and near PSRs. It is currently unknownhow the morphology of the ice and the thermal conductivity of the material are influenced by thiseffect, although an increase in thermal conductivity with increasing cementation is anticipated.An application of such thermal conductivity measurements is the extraction of water from icyregolith. For future in-situ missions and laboratory-based experiments, it is necessary to evaluatethe thermal conductivity of ice-bearing materials. This knowledge will contribute to the optimization of heating methods and the development of thermal models.