Investigation of humidity control via membrane separation for advanced Extravehicular Mobility Unit (EMU) application

摘要

Humidity must be controlled in the extravehicular mobility unit (EMU) to prevent visor fogging, to preclude buildup of water that can reduce vent flow and promote corrosion of system components, and for the comfort of the crew member. Techniques currently considered for control of humidity in the EMU include a condenser/heat exchanger with a second-stage rotary water separator; combined humidity/carbon dioxide (CO2) control using solid-amine technology; combined CO2/humidity control using a liquid electrolyte; and humidity control using a desiccant bed. However, NASA is considering alternative technologies--including membrane technology--that are less complicated and have lower power requirements. The objective of this program was to investigate the use of membrane-based technology to control humidity in the EMU. We met this objective by designing, constructing, and testing breadboard hollow-fiber dehumidification modules for this application. During a 90-day test, the performance of these modules remained virtually constant, indicating that long-term, reliable performance is feasible with this technology. Based on these results, a prototype dehumidification subsystem was designed. This membrane-based subsystem would be very small, have a low mass, and require little power. Consequently, we recommend that a preprototype dehumidification subsystem be constructed and tested under the conditions expected to be present in the EMU. Long-term tests (90 days or more) would be conducted to verify the reliability of this technology.