b'Engineer Innovation | Aerospace & DefenseIncident Solar Energy Incident Solar Energy 2. Transient runs require a long time to converge. Figure 5 shows the layer temperature from a transient analysis of a patch of lunar surface. The model was run for 30 lunar days (over two Earth years) and the lower layers are not at their final temperatures. This problem can be mitigated by assigning valid initial temperatures to each layer. Suggested initial temperatures for a number of different lunar latitudes are given in table 2. Specularly Reected Solar Energy Diffusely Reected Solar EnergyFrom figure 5 it can be seen that the Figure 5: Specular and diffuse reflection onto bottom face temperature of the lunar surface reaches its correct, periodic, temperature very quickly and does not appear to be 300 meters (m) is required to get within 1significantly affected by the temperature K of the correct temperature. At higherof the lower layers. Since a vehicle on latitudes, or at night, the disk size rthe surface will only interact with the equired for a given temperature error willsurface layer, this suggests that it may be smaller as the cooler surfaces meansnot be necessary to model all the layers. that the difference between deep space and lunar surface temperatures isThe lunar surface model was run in two reduced. additional configurations, with only the fluff and surface layers and with only the To represent the lunar surface and itssurface layer. Figure 6 shows the properties, there is a single layer of solidtemperature of the lunar surface at 45 elements to represent the fluff layer andlatitude when modeled in all three four layers of solid elements to representconfigurations. The daytime the regolith. The regolith layers havetemperatures are not significantly increasing thickness with increasingaffected by how many layers are used in depth. The thicknesses are: fluff, 20the model, however, the night time millimeters (mm); regolith 60mm,temperatures do show significant 80mm, 160mm and 320mm to give thevariation. Modeling just the fluff and total of 620mm. surface layers results in a lunar surface temperature that is 30C below the Whilst the model is very detailed, andtemperature predicted by the full model. the results correlate well with measuredModeling just the surface layer gives a lunar temperatures, it does have somelunar night temperature 100C below disadvantages:that predicted by the full model. For a vehicle in operational mode where all 1. For a steady-state analysis, thesurfaces are relatively warm, the temperatures of the lower layers arechanges in the much colder, surface not accurate. Given the relativelytemperatures from using the simpler long lunar day, objects on the lunarmodel may not be significant and the surface are often very close to steadymodel using just the fluff and surface state equilibrium; therefore, steadylayers would be acceptable. For a state analysis is valid. The lowest layerdetailed, night survival analysis, it would included in the model is essentiallybe prudent to use the full model.isothermal throughout the lunar day and its temperature is determinedDemonstration of the calculation of the by the average solar flux received atsolar loads was performed with a simple the top layer during a lunar day. In amodel consisting of a one meter black steady state analysis there is eithercube, with its lowest face horizontal, one full sun or no sun and the resultantmeter above the planet surface. For this temperature will not be correct.case, the lunar surface was assumed to This can be mitigated by fixing thehave a solar absorptivity of 0.8, a diffuse temperature of the lower layer, but thereflectivity of 0.1 and a specular problem still exists in the layers above,reflectivity of 0.1. The simplest validation although to a lesser extent.case was at a latitude of 0. The values of 40'