Lightweight, Flexible, Freezable Heat Pump/Radiator for EVA Suits
- Created on Friday, 01 August 2014
The absorption cooling process can be used to provide portable, regenerable refrigeration and air conditioning for recreation, transportation, and medical applications.
Lyndon B. Johnson Space Center, Houston, Texas
For space exploration missions that may require extended stays and extensive extra-vehicular activity (EVA) operations, the temperature control system must be lightweight, rugged, non-venting, and repairable in space.
This innovation is an absorption heat pump with a flexible radiator that vents very little water and offers reduced size, lighter weight, conformability, rugged construction, and freeze tolerance. The heat pump absorbs a crewmember’s metabolic heat and rejects it via radiation to the environment. Innovative materials and construction enable a very lightweight and flexible system that is rugged and easily repairable. The conformable radiator can be easily integrated with the EVA suit’s portable life support system (PLSS).
The thermal control system is a LiCl/water absorption heat pump consisting of a flexible absorber/radiator and an evaporation-cooled garment (ECG) worn by the astronaut. There are three main modes of operation: (1) storage, in which the absorber/radiator contains highly concentrated LiCl solution and is isolated from the rest of the system and maintained ready for use; (2) cooling, in which the absorber/radiator absorbs water vapor produced in the ECG; and (3) regeneration, in which the absorber is heated to drive out water and restore the LiCl solution to its original high concentration.
When used for cooling, metabolic heat generated by the astronaut is absorbed by evaporating water in the ECG. The LiCl solution in the absorber maintains a very low vapor pressure, so that evaporation can occur at less than 20 °C, which will maintain a comfortable temperature inside the EVA suit. Water vapor produced in the ECG flows into the absorber/radiator, which is built in the form of panels covering the outer surface of the PLSS. When the water vapor is absorbed into the solution, heat is generated and rejected from the system by radiation to space. The absorber/radiator is built from thin, flexible elements that enable it to conform to the shape of the PLSS and simplify integration with the EVA suit. ECG temperature is controlled by a pressure-regulating valve installed between the ECG and the absorber/radiator. After the LiCl solution has been diluted, the system must be regenerated by heating the absorber and driving out water vapor until the solution has dried out and returned to its original high concentration.
The absorber/radiator is built from flexible materials so that it will be lightweight, rugged, and easily integrated with the PLSS. The evaporation-cooled garment provides a single device that is lightweight, flexible, and replaces the current liquid-cooled garment, coolant circulating system, and sublimator used in current EVA suits.
The proposed heat pump can provide a lightweight, portable cooling unit to wear with sealed or heavy garments in hazardous environments, such as military chemical/bio protective suits, or level A HAZMAT suits needed for homeland security applications. The system can also be adapted to provide cooled garments for use under body armor by military personnel working in hot environments.
This work was done by Michael Izenson, Weibo Chen, and Scott Phillips of Creare Inc. for Johnson Space Center. MSC-24402-1