Critical Review of Thermal Management Technologies for Portable Life Support Systems

Thermal management technology is an uncelebrated but nonetheless essential requirement for all spacesuits, spacecraft, and space habitats. During extravehicular activity (EVA), spacesuits must remove metabolic heat produced by the astronaut, residual heat from the suit’s electronics, and absorbed heat from the external environment. The contribution of each of these heat sources can vary considerably, meaning a thermal control system must be able to actively adapt to changing heat loads to keep the suit’s internal temperature within the narrow band safe for human occupation. Currently, both NASA’s Extravehicular Mobility Unit (EMU) and the Russian Orlan spacesuit use water-ice sublimation to provide cooling. This method has proven reliable, but improvements and optimizations will need to be made for future deep space exploration. This system will not operate in a Martian atmosphere and significant mass reductions and improvements in portability must be made to support planetary EVAs. This paper will present a study of current thermal management techniques in development for planetary spacesuits and habitat systems. These include evaporative cooling, phase change and solid state heat exchangers, variably emissive electrochromic radiator devices, and variable geometry radiators (mechanical louvers). An analysis of the state of the art and Technology Readiness Level (TRL) of these technologies will be presented. Recommendations will be made for future research and where these technologies would best fit into a lunar or Mars mission system architecture. Analysis is directed towards technologies with potential use in Portable Life Support Systems (PLSS) integrated into next generation spacesuits for planetary surface EVAs on the Moon and Mars.