This paper proposes a lunar long-duration method that uses a characteristic of a very low thermal conductivity of lunar regolith. The principle of this method is to put a heater in at the desired depth of the regolith and heat up the regolith layer during lunar daytime. Because of the very low thermal conductivity of regolith, stored heat in regolith propagates gradually and raises the surface temperature during the cold lunar night. By this method, a lunar lander will be kept warm passively during a cold lunar night. A temporospatially small-scale experimental apparatus that simulates the lunar surface environment was fabricated and the feasibility of a passive thermal control method with no electrical power during lunar nighttime was evaluated. The effectiveness of the proposed method was analytically evaluated by considering the relation between experimental result and actual lunar environment. Nomenclature C p = constant pressure specific heat D = depth where the constant temperature area exists E = Young's modulus F = constant depending on particle emissivity f = heating frequency k c , k r , k s = thermal conductivity by contact, radiation, and regolith constituent, respectively L = thermal diffusion length P = pressure R = particle radius S, S F , N A , N L = constants depending on packing structure T space = cosmic background radiation, 2.73K T surface = temperature of lunar surface α = solar absorptivity ε = emissivity λ = thermal conductivity μ = Poisson's ratio ρ = density σ = Stefan-Boltzmann constant φ = solar elevation angle Subscripts E = experimental apparatus M = actual lunar surface

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A lunar long duration method which utilizes a characteristic of a very low thermal conductivity of lunar regolith has been proposed. The principle of this method is to put heater in desired depth of the regolith and heat up the regolith layer during lunar daytime. Because of the very low thermal conductivity of regolith, stored heat in regolith propagates gradually and raises the surface temperature at cold lunar night. By this method, a lunar lander will be kept warm passively during cold lunar night. In this paper, a temporospatially small-scale experimental apparatus which simulate lunar surface environment was fabricated and thermal cycling condition and heater setting position was calculated by comparing lunar environment, and thermophysical properties of the lunar regolith and regolith simulant used in this work. The feasibility of a passive thermal control method with no electrical power during lunar night time was evaluated.