THERMAL, CHEMICAL, AND RHEOLOGICAL ANALYSIS OF LUNAR HIGHLAND SIMULANTS

Permanent settlement of the lunar surface will require structures that can withstand micrometeorite impacts, radiation, and other hazards. Bricks made from lunar regolith will be cost-effective compared to transporting materials from the Earth. Developing the technology for in situ construction requires using effective lunar simulants. Several are currently available; the purpose of this study was to assess the variability of physical properties resulting from different bulk compositions.

Two lunar highland simulants, NU-LHT-5M HQ and CSM-LHT-1G, were characterized using X-ray fluorescence spectroscopy, pycnometry, calorimetry, viscometry, and light flash analysis. NU-LHT-5M HQ is the glass component of a NASA simulant under development, and CSM-LHT-1G is a partially crystalline simulant made of several components. Their densities are similar in both glass and powder forms, in the range 2700-2800 kgm^-3. Heating at 30 Kmin^-1, NU-LHT-5M had a glass transition (T_g) at 788°C and reached liquidus (T_liq) at 1459°C. Powdered CSM-LHT-1G reached T_g at 616°C and T_liq at 1534°C. Remelted glass CSM-LHT-1G reached T_g at 750°C and T_liq at 1425°C. Total enthalpy required to heat NU-LHT-5M HQ glass to 1600°C was ~1681 Jg^-1K^-1 and for CSM-LHT-1G powder it was ~2275 Jg^-1K^-1. At 1600˚C, the viscosity of molten NU-LHT-5M HQ was 1.9 Pa·s, and for CSM-LHT-1G it was 2.6 Pa·s. Thermal diffusivity of NU-LHT-5M glass was 0.55mm²s^-1 at 25°C and 0.52mm²s^-1 at 600°C, and thermal diffusivity of CSM-LHT-1G was 0.54mm²s^-1 at 25°C and 0.52mm²s^-1 at 600°C. Thermal conductivity of NU-LHT-5M HQ glass was 1.225 Wm^-1K^-1 at 25°C and 1.472 Wm^-1K^-1 at 600°C. Thermal conductivity of CSM-LHT-1G was 1.200 Wm^-1K^-1 at 25°C and 1.434 Wm^-1K^-1 at 600°C.

These results reveal that once molten, the two simulants behave quite similarly despite their different chemical compositions. This suggests that moderate variation of the highland regolith material will not significantly impact the performance and the design of the equipment that may be used to process them.