Thermal conductivity of particulate basalt as a function of density in simulated lunar and Martian environments

Abstract

As part of an effort to properly define the thermophysical model of the lunar surface, experimental data have been obtained to determine the thermal conductivity of a particulate basalt sample (37 to 62 μ diameter) as a function of density in a simulated lunar temperature and pressure environment. A sample at six different densities ranging from 0.79 g/cm3 to 1.50 g/cm3 was investigated by using Ronald B. Merrill's method of thermal conductivity measurement. Recent measurements of the conductivity of the Apollo 11 lunar sample are included for comparison. Kenneth Watson's equation for the thermal conductivity of powders in a vacuum, K = A + BT3, has been curve-fitted to the vacuum data for each density. The coefficients A and B are useful for application in thermophysical models of the lunar surface. Thermal conductivity data were also obtained under simulated Martian temperature and pressure environment at four of the densities. A separate effort was made to determine the maximum density obtainable with the specific sample to draw qualitative conclusions concerning the ambiguous value of density yielded by the Russian Luna 13 in situ density experiment. Thermal conductivity of particulate basalt was found to be a definite function of density in a simulated lunar environment and that function has been established. However, under simulated Martian environmental conditions, density and temperature had only a slight effect on thermal conductivity.