Analysis of the thermal environment in the LuNaDrone exploration mission of lunar lava tubes

Lunar Nano Drone (LuNaDrone) is a small spacecraft capable of performing autonomous flight in the lunar near-surface environment, whose primary application is a mission of exploration of lunar pits to detect potential openings to lunar lava tubes. Throughout the phases of this mission, the spacecraft has to deal with several thermal environments and among these, the lunar surface operations can be critical for the thermal control design. A meaningful thermal analysis requires correct modelling of both the thermal environment and the spacecraft, on the ground and in flight. The proposed modelling approach, implemented in Thermal Desktop, aims to provide a preliminary evaluation of the radiative thermal fluxes incident on the spacecraft faces throughout the surface operations and flight segments, in order to qualitatively validate the flight manoeuvres model implementation and to identify the most critical thermal scenario. Starting from temperature data of Apollo 17 and Lunar Reconnaissance Orbiter, a thermal model was designed for the lunar surface and for a lunar pit, characterizing them for the Mare Tranquillitatis Pit case. A 12U test box has been modelled in order to evaluate heat fluxes on the spacecraft, exploiting Thermal Desktop's Assembly and Symbols features to implement the flight manoeuvres in the thermal model. The analyses were performed for three different local times and four cardinal directions approaches to the pit. The results showed how the modelling approach correctly allows the implementation of flight manoeuvres in the thermal model. Regardless of local time or spacecraft orientation, the results show that the most critical radiative scenario is not one of the flight segments, but the transmission phase, after the propellant has been almost completely depleted and the spacecraft finds itself in a highly radiative environment on the lunar surface.