Hollow Fiber Flight Prototype Spacesuit Water Membrane Evaporator Design and Testing

The Spacesuit Water Membrane Evaporator (SWME) is a heat-rejection device that is being developed to perform thermal control for advanced spacesuits. The SWME takes advantage of recent advances in micropore membrane technology, resulting in a robust heatrejection device that is potentially less sensitive to contamination than is the sublimator. Cooling is achieved by circulating water from the liquid cooling garment (LCG) through hollow fibers (HoFi’s), which are small hydrophobic tubes. Liquid water remains within the hydrophobic tubes, but water vapor is exhausted to space, thereby removing heat. The current design was based on a previous design that grouped the fiber layers into stacks, which were separated by small spaces and packaged into a cylindrical shape. This was developed into a full-scale prototype that consists of 14,300 tube bundled into 30 stacks, each of which is formed into a chevron shape, separated by spacers, and organized into three sectors of 10 nested stacks. The newest design replaced metal components with plastic ones, eliminated the spacers, and has a custom-built, flight-like backpressure valve mounted on the side of the SWME housing to reduce backpressure when fully open. A number of tests were performed to improve the strength of the polyurethane header that holds the fibers in place while the system is pressurized. Vacuum chamber testing showed heat rejection as a function of inlet water temperature, and water vapor backpressure was similar to that of the previous design. Other tests pushed the limits of tolerance to freezing and showed suitability to reject heat in a Mars pressure environment with and without a sweep gas. Tolerance to contamination by constituents expected to be found in potable water produced by distillation processes was tested in a conventional way by allowing the constituents to accumulate in the coolant as evaporation occurs.