b'Aerospace & Defense | Engineer InnovationThermal effect Moon MarsDirect solar Yes YesDiffuse (scattered) solar flux No Yes (during dust storm)Atmospheric solar attenuation No YesRadiation to effective sky temperature Yes, to deep space Yes, time varyingAlbedo Yes YesSurface vehicle interaction (radiation) Yes YesConvection No YesTable 1: Surface vehicle thermal effects Figure 1: Atmospheric and planet surface formThe lunar environment has no atmosphere and the Martian atmosphere, compared to the Earth, has very low atmospheric pressure.The lack of atmosphere on the Moon results in a large temperature variation with latitude, at the equator this can be as high as 100 degrees Celsius (C), down to -200C at the poles.With the lunar day lasting 29.5 Earth days and a two-week night, any vehicle on the lunar surface will reach likely thermal equilibrium with its surroundings. The vehicle will cause shadowing which will result in local cooling of the surface to very low temperatures. Since the vehicle will be radiation cooled, these cold shadowed regions can result in lower vehicle temperatures. Figure 2: Simple plate over disk modelDespite the low pressure in MarsThe presence of atmosphere on a planet atmosphere it still has a significantalso means that convective heat transfer impact on the thermal design of vehiclesmay need to be addressed. For a bound for Mars. This atmosphere resultsterrestrial model, free convection and in some convection heat transfer fromradiation are typically of similar order of vehicle surfaces and, more significantly,magnitude. If the air is moving because results in dust storms that considerablyof wind, for example, then convection change the transparency of thebegins to dominate the heat transfer. On atmosphere. The results are a reductionMars, radiation is typically the dominant in direct solar illumination, an increase inmode of heat transfer but convection is diffuse sky illumination and in skystill significant. The most accurate temperature. The first effect will result inmethod of modeling convective heat a decrease in vehicle temperature, thetransfer is with computation fluid others lead to an increase indynamics (CFD). This can provide very temperature. Detailed analysis isaccurate modeling of convection, but required to determine the overall effect.requires a very detailed model with a The Martian regolith is a better thermalvery fine mesh (compared to a typical conductor than the lunar regolith, butspacecraft thermal model) and is there is still significant interactiontypically overkill for a situation where between a vehicle and the planetconvection is not the dominant mode of surface. heat transfer. A simpler, and more practical, approach is to simply specify a The surface vehicle thermal effects areheat transfer coefficient and shown in table 1. atmospheric temperature for any 37'