This research addresses the significant and unprecedented 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 -240ºC to 30ºC.  The internal electronics essential to these rovers, however, ideally operate in the narrow range from -15ºC to 40ºC.  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, analyzing 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) Polymer insulators protect the thermally sensitive actuators from the extremely cold wheels that they drive.  This paper demonstrates how MoonRanger employs these considerations to display robust thermal regulation keeping most avionic components to temperatures between 0ºC and 40ºC at surface temperatures ranging from -215ºC to 30ºC. 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.

Prof. William (Red) Whittaker (Chair)

Prof. Zachary Manchester

Prof. Satbir Singh

Kevin Tracy