Thermal Management Considerations For Lunar Polar Micro-Rovers

This research addresses the significant challenge of thermal regulation for lunar polar micro-rovers. These are distinct from priors by way of very small size, mass, and power, but particularly for the extremes of ambient environment in which they must operate. On the lunar poles, rovers experience temperatures ranging from $-240^{\circ}\mathrm{C}$ to $30^{\circ}\mathrm{C}$ . The internal elec-tronics essential to these rovers, however, ideally operate in the narrow range from $0^{\circ}\mathrm{C}$ to $40^{\circ}\mathrm{C}$ . Since there is no atmosphere on the Moon, the mechanism of atmospheric convection that dominates on Earth does not apply, and only solutions that rely on the weaker mechanisms of radiation and conduction pertain. Small rovers lack the thermal inertia and mass budgets that enable traditional thermal solutions that pertain to their larger counterparts. Early micro-rover missions last a single lunar illumination period and end at sundown. For that reason night survival is beyond scope and incorporation of isotope heating is not incorporated into this research. MoonRanger is embraced as an exemplar for designing, ana-lyzing and illustrating the principles and solutions for the new class of lunar polar micro-rovers. MoonRanger is the world's first lunar polar micro-rover destined for the lunar south pole to measure ice. The research distinguished critical insights. 1) There is a need for significant heat rejection due to the combination of sun impingement and the significant electrical power on order of 65 watts that manifests as heat within the rover. 2) Aggregating all sensitive avionics and batteries in a monolithic enclosure provides multiple advantages of thermal inertia and conductive pathway to remove excess heat out to cold space via the radiator. 3) The enclosure's sides are lined with Multi-Layer Insulation to mitigate radiative heat transfer with cold lunar regolith. 4) Due to terrain irregularities the rover's radiator deck can tilt into the sun causing unwanted heating. To prevent this, the solar panel is integrated with the chassis so that it casts a shadow on the radiator to reduce sunlight incidence. 5) The solar panel also features high-emissivity films that increase heat rejection, thus decreasing temperature and increasing cell efficiency. 6) Poly-mer insulators protect the thermally sensitive actuators from the extremely cold wheels that they drive. This paper demonstrates how MoonRanger employs these considerations to display ro-bust thermal regulation keeping most avionic components to temperatures between $0^{\circ}\mathrm{C}$ and $40^{\circ}\mathrm{C}$ at surface temperatures ranging from $-215^{\circ}\mathrm{C}$ to $30^{\circ}\mathrm{C}$ . The research establishes baseline considerations for future solar powered polar micro-rovers and serves as an archetype for this class of rovers that are yet to come.