Thermal design challenges for lunar ISRU payloads

Several Concurrent Design Facility (CDF) studies were performed at ESA ESTEC to investigate different lunar in-situ resource utilization (ISRU) payload concepts. There are numerous technological challenges mainly associated with the maturity of the different processes and associated components, but also regarding thermal design aspects. A wide range of dissipated powers, high process temperatures, batch processes, and the thermal lunar surface environment have proven to be major design drivers for the ISRU payloads.

Carbothermal reduction with methane, ilmenite reduction with hydrogen, and molten salt electrolysis were investigated. The ISRU processes are characterized by process temperatures from 850 degC to 1300 degC and downstream process units of up to 500 degC. The investigated concepts required from 150 W to 900 W of heating power over several hours per batch, for multiple batches over the course of a lunar day. A further challenge is the thermal process control for thermally inert ovens with regolith. The limitations of payloads, regarding dimensions, mass, accommodation and allowable heat fluxes at the interfaces to the lander, restrict the thermal control possibilities further. All this is placed in a challenging lunar surface thermal environment.

In this paper the thermal designs for two ISRU payloads are described along with the respective results. Eventually potential thermal control technologies are sketched to overcome the shortcomings of the current design limitations for lunar ISRU payloads.