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In 2007, the architecture of the Orion Environmental Control and Life Support System went through a major reassessment driven by overall vehicle weight considerations. The changes were initiated with the challenge to switch from a two fault tolerant based configuration to one that is one fault tolerant. This paper describes this design evolution.

An analysis model has been developed for analyzing/optimizing the integration of a carbon dioxide removal assembly (CDRA), CO2 compressor, accumulator, and Sabatier CO2 reduction assembly. The integrated model can be used in optimizing compressor sizes, compressor operation logic, water generation from Sabatier, utilization of CO2 from crew metabolic output, and utilization of H2 from oxygen generation assembly. Tests to validate CO2 desorption, recovery, and compression had been conducted in 2002-2003 using CDRA/Simulation compressor set-up at NASA Marshall Space Flight Center (MSFC). An analysis of test data has validated CO2 desorption rate profile, CO2 compressor performance, CO2 recovery and CO2 vacuum vent in the CDRA model. Analysis / optimization of the compressor size and the compressor operation logic for an integrated closed air revitalization system is currently being conducted

The TIMES system was evaluated to determine its ability to process reverse osmosis (RO) brine as one of the Advanced Water Processor steps. Since preliminary testing performed in 1998 showed that the membrane typically used in the process (Nafion 117) offered a very poor ammonia rejection, a search for an alternate membrane exhibiting high ammonia rejection capability was initiated under NASA-JSC funding. This investigation has resulted in the selection of a PolyVinylAlcohol (PVA) composite membrane as a replacement. When processing RO brine and untreated human urine as feeds, the Pervap 2201 membrane showed a 96% ammonia rejection over a large range of ammonia concentration. The water permeation rates in both laboratory-scale and pilot scale testings were also similar to the Nafion. The water permeance of the Pervap 2201 was approximately 7.5 kg/h/m2/atm (1.1 lb/h/m2/psi).

Carbon dioxide reduction in a closed loop life support system recovers water from otherwise waste carbon dioxide and hydrogen. Incorporation of a carbon dioxide reduction assembly (CRA) into the International Space Station life support system frees up thousands of pounds of payload capacity in the supporting Space Shuttle that would otherwise be required to transport water. Achievement of this water recovery goal requires coordination of the CRA design to work within the existing framework of the interface systems that are either already on orbit or well advanced in their development; namely, the Oxygen Generator Assembly (OGA), Carbon Dioxide Removal Assembly (CDRA) and Water Processor Assembly (WPA). The Oxygen Generation System (OGS) rack is in its final design phase and is scarred to accept later installation of the CRA.

The TIMES is an evaporative water processor which has shown great theoretical potential for providing reliable and efficient production of high quality water. The test results of the system have however fallen short of the predicted performances. A thorough systems analysis has identified the condensing heat exchanger as a primary source of the shortcomings of the assembly. This condenser, along with three other heat exchangers in the system, have been redesigned and integrated into a new “Regenerator” that is predicted to significantly lower the power consumption and improve both the operating stability and product water quality.

The ability of a cabin air condensing heat exchanger to survive the depressurization of a space module is limited. The phenomenon that limits a heat exchanger's survivability is freezing caused by the cooling effect of the condensate evaporating on the air side of the condensing heat exchanger and freezing the coolant water. There are several options for solving the problem. These options include: Isolate the air side of the heat exchanger. Design the heat exchanger to meet the demands of freezing. Increase the coolant temperature and/or the coolant flow rate. Control the rate of depressurization.