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

• A novel analytical methodology is presented for temperature study on lunar surface and subsurface.
• The methodology is suitable to determine temperature profile/variation on the Moon with time and with depth
• The less dense regolith fluff at the lunar surface found to give very high thermal insulation.
• Lunar regolith subsurface temperature remains relatively constant below a depth of 30 cm.
• Due to albedo radiation from nearby lunar surfaces, the temperature on a habitat is found higher than that on the lunar surface.

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 102.4 K to 387.1 K. 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 132.3 K from the maximum daytime magnitude of 387.1 K within the first 30 cm at which point it then remains constant with increasing depth. At night, the temperature increases from the minimum magnitude of 102.4 K to 254.8 K within the outermost 30 cm. 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 457 K (about 70 K higher than the lunar surface temperature) and displayed a drop of 138 K within the first 30 cm depth of regolith cover. The minimum temperature at night increased 80.3 K over the surface temperature to reach 182.7 K while displaying an increase of 137.2 K through the outermost 30 cm. 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 30 cm). 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.