This work aims to provide thermal engineers a set of empirical equations between dust deposition rates and the modification of thermo-optical properties of radiators for lunar surface missions.
For the thermal engineer involved in the design of hardware dedicated to operating on the lunar surface, lunar dust is one of the biggest challenges. The smallest fraction of the sharp-edged small dust particles easily adheres to technical surfaces. There are natural and artificial sources which cause the dust to be levitated on the surface of the Moon. Not only the landing or roving of vehicles stirs up and moves lunar dust, but also naturally occurring electrical charge differences. For the thermal engineer the presence and movement of dust means a modification of thermo-optical properties of thermal control surfaces. The thermal control surface in the focus of the present work are radiator surfaces, i.e., one specific white paint (AZ93) and one Second Surface Mirror tape (AgFEP), due to a limited data set from literature.
Currently there is a missing link between the dust deposition rates and the modification of radiator surfaces reported, in literature. Literature on dust deposition is based on flight data and concerns natural lunar regolith, whereas the literature on radiator modification is scarce and the studies were performed with lunar dust simulant materials. The present work is bridging this gap for radiator sizing in early design phases.
The solar absorptivity of radiators is much more affected than their IR emissivity, due to the high emissivity of radiators and the lunar dust alike. The modification factor for the solar absorptivity varies from 1.1 to almost 6 for dust deposition of 100-600 µg/cm2, but depends on type of radiator coating, radiator substrate, and the conversion assumptions between natural regolith properties and lunar dust simulant. The uncertainty associated with the results will be presented along with an approach to combine the results with common aging related modifications.
The conducted study was based on literature data. It is meant as a first steppingstone toward design guidelines for ‘dusted end-of-life” properties for thermal control coatings for thermal engineers. Further material science based in depths investigations are necessary and are currently initiated at ESA, to have more robust modification factors for upcoming missions to the Moon.