For short durations, evaporative heat rejection systems are a very effective way of removing heat from spacecraft. Future NASA vehicles, such as the Crew Exploration Vehicle (CEV), will require non-radiative heat rejection systems during at least a portion of the planned mission, just as their predecessors have. While existing technologies are available to modify, such as Apollo era sublimators, or the Space Shuttle Flash Evaporator System (FES), several new technologies are under development or investigation to progress beyond these existing heat rejection systems. Examples include the Multi-Fluid Evaporator developed by Hamilton Sundstrand, improvements upon the Contaminant Insensitive Sublimator originally developed for the X-38 program, and a Compact Flash Evaporator System. Other possibilities evaluate new ways of operating existing designs. The new developments are targeted at increasing operating life, expanding the environments in which the system can operate, improving the mass and volume characteristics, or some combination of these, and other improvements.
This paper captures the process and results of a preliminary trade study performed at the NASA Johnson Space Center to compare the various existing and proposed evaporative heat rejection systems for the CEV. Because the new systems are still in development, and the information on existing systems is extrapolated, this trade study is not meant to suggest a final decision for future vehicles. The purpose of this “preliminary” trade study is to identify candidate technologies, provide preliminary data on these technologies, and to identify strengths and weaknesses of the different designs. Prototypes of all three of the technologies currently in development will be built and tested during the next year and a half. The performance demonstrated by these future prototypes is what should be used in making final selections for future vehicles.