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Risk assessments performed on the Sabatier Carbon Dioxide Reduction Assembly (CRA) indicated a need to prevent liquid water from reaching the vacuum vent as a result of component failures. Liquid water can freeze at the vacuum vent line pressure and result in a cascade failure to the Carbon Dioxide Removal Assembly (CDRA) that shares the same vacuum vent line. Since the CDRA is a critical piece of life support equipment, this failure mode has a Catastrophic hazard severity. This paper describes the development of a large and a small absorber to protect the vacuum line from water entry. The component requirements, configurations and capabilities are described. Application of this absorber technology to other system needs is also proposed. Development of these critical components will help to achieve the desired technology maturity for the CRA and bring the CRA technology closer to a flight design.

The Volatile Removal Assembly Flight Experiment (VRAFE) was performed in May of 1999, on board Shuttle Flight STS-96 to support the development of the International Space Station (ISS) Water Recovery System (WRS). The objective of this experiment was to address concerns in the performance of a two-phase, catalytic reactor in a microgravity environment. During the experiment, an unexpected finding was discovered when the VRAFE Gas/Liquid Separator (GLS) failed to separate gas from the reactor outlet stream. The VRAFE GLS was a two-membrane (flat sheet hydrophobic and hydrophilic membrane) gas trap. Flight data as well as the post-flight failure investigation determined that the GLS hydrophobic membrane failed as a result of very fine hydrophilic catalyst particles from the VRAFE reactor that had contaminated the surface of the hydrophobic membrane.

A trade study conducted in 2001 selected a rotary disk separator as the best candidate to meet the requirements for an International Space Station (ISS) Carbon Dioxide Reduction Assembly (CRA). The selected technology must provide micro-gravity gas/liquid separation and pump the liquid from 69 kPa (10 psia) at the gas/liquid interface to 124 kPa (18 psia) at the wastewater bus storage tank. The rotary disk concept, which has pedigree in other systems currently being built for installation on the ISS, failed to achieve the required pumping head within the allotted power. The separator discussed in this paper is a new design that was tested to determine compliance with performance requirements in the CRA. The drum separator and pump (DSP) design is similar to the Oxygen Generator Assembly (OGA) Rotary Separator Accumulator (RSA) in that it has a rotating assembly inside a stationary housing driven by a integral internal motor[1].

When technologies are traded for incorporation into vehicle systems to support a specific mission scenario, they are often assessed in terms of “Technology Readiness Level” (TRL). TRL is based on three major categories of Core Technology Components, Ancillary Hardware and System Maturity, and Control and Control Integration. This paper describes the Technology Readiness Level assessment of the Carbon Dioxide Reduction Assembly (CRA) for use on the International Space Station. A team comprising of the NASA Johnson Space Center, Marshall Space Flight Center, Southwest Research Institute and Hamilton Sundstrand Space Systems International have been working on various aspects of the CRA to bring its TRL from 4/5 up to 6. This paper describes the work currently being done in the three major categories. Specific details are given on technology development of the Core Technology Components including the reactor, phase separator and CO2 compressor.

This paper presents and discusses the results of an integrated 4-Bed Molecular Sieve (4BMS), mechanical compressor, and Sabatier Engineering Development Unit (EDU) test. Testing was required to evaluate the integrated performance of these components of a closed loop atmosphere revitalization system together with a proposed compressor control algorithm. A theoretical model and numerical simulation had been used to develop the control algorithm; however, testing was necessary to verify the simulation results and further refine the model. Hardware testing of a fully integrated system also provided a better understanding of the practical inefficiencies and control issues, which are unavailable from a theoretical model.

Closed-loop inhabited spacecraft, including a space suit, require removal of carbon dioxide from the breathing atmosphere. A membrane device that separates CO2 from breathing air can effectively control CO2 levels in the breathing loop by venting the carbon dioxide directly to the vacuum of space. Such a membrane device requires no regeneration and, therefore, imposes no limitations on mission length. Systematic studies have expanded our knowledge of the parameters most critical to the successful development of a membrane carbon dioxide removal system. The membrane type disclosed in this paper is an immobilized liquid membrane (ILM) in which the liquid is engineered to facilitate the transport of carbon dioxide while inhibiting the progress of oxygen. Selectivity superior to that achieved in previously published studies has been demonstrated and has approached values desired for an Extravehicular Mobility Unit (EMU) system.