Determination of temperature variation on lunar surface and subsurface for habitat analysis and design

Abstract

The ambient environmental factors present on the lunar surface pose some of the most difficult challenges for the success of a long-term human settlement on the Moon. Aside from the dangerous radiation levels and hypervelocity micrometeoroid impacts, the equatorial temperature on the surface of the Moon can range from 102.4K to 387.1K. These extremes pose a variety of complications like thermal expansion and contraction, which can, in turn, alter the static, dynamic, and frequency response of a structure. This paper first presents the analytical study of the surface and subsurface thermal/heat flow environments of a potential habitat site located at the Equator of the Moon using a general equation that was developed based on the thermodynamic principle of heat flow to determine the temperature variation/gradient with time as well as depth. This method was then applied, with appropriate modifications, to determine the temperature variation with time and through depth of a 1-m thick regolith shielding layer surrounding a lunar structure. The solution to the general equation was determined through the use of the fourth-order Runge–Kutta technique of numerical integration. The analysis results showed that the outermost layer of regolith fluff has very strong insulating capabilities causing the temperature to drop 132.3K from the maximum daytime magnitude of 387.1K within the first 30cm at which point it then remains constant with increasing depth. At night, the temperature increases from the minimum magnitude of 102.4K to 254.8K within the outermost 30cm. When considering a layer of regolith shielding atop a lunar habitat, the added albedo radiation input from the adjacent lunar surface to the structure increased the maximum daytime surface temperature to 457K (about 70K higher than the lunar surface temperature) and displayed a drop of 138K within the first 30cm depth of regolith cover. The minimum temperature at night increased 80.3K over the surface temperature to reach 182.7K while displaying an increase of 137.2K through the outermost 30cm. In general, throughout the lunar cycle, it was observed that at a fixed point in time, as the depth within the regolith increases, the temperature variation throughout the lunar cycle decreases and the temperature ultimately remains constant beyond a certain depth (observed to be approximately 30cm). The framework of this study, which was completed considering a habitat at the lunar equator, can also be used at different locations of the Moon to study their adequacy for long-term colonization missions.