Heat Rejection Architectures for Martian Spacesuits

Heat rejection is an essential function of spacesuit Portable Life Support Systems, with the design of an optimised system heavily dependent on the ambient conditions outside the spacesuit. Flight-proven heat rejection systems have almost exclusively used evaporation or sublimation of water as the ultimate sink for metabolic and system heat, in both orbital and lunar environments. However, the Martian environment presents unique challenges for this architecture. Relatively high ambient pressure, high air temperatures and dust contamination may all interfere with the operation of existing evaporator designs. his paper presents a comparative trade study of four architectures for heat rejection in a Martian Portable Life Support System: water evaporators, generalised fluid evaporators/boilers, forced-convection heat exchangers and emissive radiators. Water and general-fluid evaporators use the same principle of operation, rejecting heat in the open-loop phase change of a volatile fluid. Forced-convection heat exchangers are a low TRL technology for space application, but have promising application in hightemperature applications such as surface nuclear power and have extensive terrestrial industrial heritage. Emissive radiators are commonly used for fixed systems but present unique challenges for dust fouling in surface operations on Mars. In addition, the use of heat pumping to increase the temperature of heat rejection is also evaluated. Considerations of size, weight and power are evaluated for different EVA and mission profiles, as well as the broader operational limits and implications of each architecture. The operational characteristics of each architecture, and a potential implementation, are presented for baselining against future developments. These operational characteristics are being used to develop a highly parametric human-in-the-loop heat rejection testbed, which is still in development.