A lunar surface environment model for the Thermal Moon Simulator (TherMoS)

Abstract

The surface of the Moon is a harsh thermal environment for spacecrafts and astronauts with global temperature extremes between almost 400 K at a subsolar point on the lunar equator around lunar noon and 40 K or less in permanently shadowed craters at the lunar poles. On a local scale the temperature varies even more due to the unique thermal properties of the lunar regolith and the lack of atmosphere. craters, boulders, or mountain ranges can significantly alter local surface temperatures, which in turn have an impact on the accessibility and safety for regions of interest as well as on the performance of surface operated spacecrafts. TherMoS (Thermal Moon Simulator) is a MATLAB® based tool adapted to the demanding thermal conditions on the lunar surface. Its objectives are to provide mission planers and spacecraft designers a means of forecasting the thermal environment at points of interest in a given period during a lunar day. The tool is currently under development at the Institute of Astronautics at the Technische Universitat Munchen. The tool is composed of several subsystem models (i.e. for mission & schedule, environment, Sun & orbit, spacecraft, and overall geometry), each of which is further subdivided into individual and more specialized submodels. In this paper the environmental subsystem as the backbone of the simulation is presented. It comprises a topographic model based on publicly available remote sensing data, a regolith layer model, which accounts for the properties and thermal behavior of the Moon‟s outermost layer, a boulder model, and a crater model to account for local temperatures. In this paper we present the basic equations for the geometry of the crater and boulder model, the temperature dependent thermal conductivity, λ(T), for specific heat, cP(T), and for the regolith and mare basalt density ρ(T). Moreover, the vector-based calculations for solar flux, depending on global latitude and longitude, as well as the position in the crater or on a boulder is presented. Also the effect of local slope and position inside a crater and on a boulder on the surface temperature is shown. The obtained temperatures up to 395 K and temperature profile for lunar daytime are in good agreement with earlier models. The calculated lunar nighttime temperatures of 167 K are higher than those obtained elsewhere. At the same time lunar day temperatures differ between flat plane and boulder by 20 K, and between flat plane and 18° inclined crater wall by 15 K. Further and more detailed models are necessary to assess local temperature anomalies, their time scales, and their impact on spacecrafts for future lunar surface operations.