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Carbon dioxide removal on the Shuttle is performed either by flowing cabin ventilation air through single use LiOH beds or by using the Regenerable CO2 Removal System (RCRS) (Ref 1,2,3). The RCRS was designed for single string mechanical operation with redundancy only on electrical components. It therefore can become disabled by a number of possible single point failures such as fan failure, actuator failure or a large internal leak through the beds. Because of these possible failures, LiOH must be flown on all RCRS missions to provide contingency CO2 removal. These LiOH canisters occupy valuable stowage space onboard the shuttle orbiter. The development of a new sorbent material called HS-X with significantly more CO2 removal capacity per unit volume has made much smaller sorbent bed sizes possible. With significantly smaller beds each of the single point failures can be addressed and a fully redundant RCRS can be built to fit within the existing RCRS envelope.

Designers of future space vehicles envision simplifying the Atmosphere Revitalization (AR) system by combining the functions of trace contaminant (TC) control and carbon dioxide removal into one swing-bed system. Flow rates and bed sizes of the TC and CO2 systems have historically been very different. There is uncertainty about the ability of trace contaminant sorbents to adsorb adequately in a high-flow or short bed length configurations, and to desorb adequately during short vacuum exposures. This paper describes preliminary results of a comparative experimental investigation into adsorbents for trace contaminant control. Ammonia sorbents and low temperature catalysts for CO oxidation are the foci. The data will be useful to designers of AR systems for Constellation. Plans for extended and repeated vacuum exposure of ammonia sorbents are also presented.

Research into increased capacity solid amine sorbents has found a candidate (SA9T) that will provide enough increase in cyclic carbon dioxide removal capacity to produce a fully redundant Regenerative Carbon Dioxide Removal System (RCRS). This system will eliminate the need for large quantities of backup LiOH, thus gaining critical storage space on board the shuttle orbiter. This new sorbent has shown an ability to package two fully redundant (four) sorbent beds together with their respective valves, fans and plumbing to create two operationally independent systems. The increase in CO2 removal capacity of the new sorbent will allow these two systems to fit within the envelope presently used by the RCRS. This paper reports on the sub-scale amine testing performed in support of the development effort. In addition, this paper will provide a preliminary design schematic of a fully redundant RCRS.

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 Trace Contaminant Control System (TCCS) removes most hazardous contaminants from the space station atmosphere using a carbon bed, but some must be destroyed in a high temperature catalytic oxidizer. While the oxidizer is protected from catalyst poisons by the carbon bed, if contaminant loads are greater than anticipated, the catalyst may be exposed to a variety of poisons. Thus, we studied the effect of halocarbons, sulfides and nitrogen compounds on the catalytic activity and the products produced. We found that even if poisoning occurs, the catalyst will recover, and will not produce toxic partial oxidation products.

A number of amine-based carbon dioxide (CO2) removal systems have been developed for atmosphere revitalization in closed loop life support systems. Most recently, Hamilton Sundstrand has developed an amine-based sorbent, designated SA9T, possessing approximately 2-fold greater capacity compared to previous formulations. This new formulation has demonstrated applicability for controlling CO2 levels within vehicles and habitats as well as during extravehicular activity (EVA). Our current data demonstrates an amine-based system volume which is competitive with existing technologies which use metal oxides (Metox) and lithium hydroxide sorbents. Further enhancements in system performance can be realized by incorporating humidity and trace contaminant control functions within an amine-based atmosphere revitalization system. A 3-year effort to develop prototype hardware capable of removing CO2, H2O, and trace contaminants from a cabin atmosphere has been initiated.

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.

Environmental Control and Life Support (ECLS) system functionality aboard the International Space Station (ISS) includes responding to various emergency conditions. The ISS requirements define three types of emergencies: fire, rapid depressurization, and hazardous or toxic atmosphere. The ISS has automatic integrated vehicle responses to each of these emergencies. These automated responses are designed to aid the crew in their response actions to the emergencies. The response to a hazardous atmosphere on board the ISS, including the automatic integrated vehicle response and crew actions, is the focus of this paper. Philosophies regarding the detection of and response to emergencies involving chemical releases are described. Vehicle configuration is discussed for currently supported automatic responses, and crew actions are defined for modules on orbit up to the addition of the Docking Compartment (DC1) in the assembly sequence.

Under a NASA-sponsored technology development project, a multi-disciplinary team consisting of industry, academia, and government organizations lead by Hamilton Sundstrand is developing an amine-based humidity and CO2 removal process and prototype equipment for Vision for Space Exploration (VSE) applications. Originally this project sought to research enhanced amine formulations and incorporate a trace contaminant control capability into the sorbent. In October 2005, NASA re-directed the project team to accelerate the delivery of hardware by approximately one year and emphasize deployment on board the Crew Exploration Vehicle (CEV) as the near-term developmental goal. Preliminary performance requirements were defined based on nominal and off-nominal conditions and the design effort was initiated using the baseline amine sorbent, SA9T.

In a crewed spacecraft environment, atmospheric carbon dioxide (CO2) and moisture control are crucial. Hamilton Sundstrand has developed a stable and efficient amine-based CO2 and water vapor sorbent, SA9T, that is well suited for use in a spacecraft environment. The sorbent is efficiently packaged in pressure-swing regenerable beds that are thermally linked to improve removal efficiency and minimize vehicle thermal loads. Flows are all controlled with a single spool valve. This technology has been baselined for the new Orion spacecraft. However, more data was needed on the operational characteristics of the package in a simulated spacecraft environment. A unit was therefore tested with simulated metabolic loads in a closed chamber at Johnson Space Center during the last third of 2006. Tests were run at a variety of cabin temperatures and with a range of operating conditions varying cycle time, vacuum pressure, air flow rate, and crew activity levels.

Paradoxically, trace contaminant control systems that suffer unexpected upsets and malfunctions can release hazardous gaseous contaminants into a spacecraft cabin atmosphere causing potentially serious toxicological problems. Trace contaminant control systems designed for spaceflight typically employ a combination of adsorption beds and catalytic oxidation reactors to remove organic and inorganic trace contaminants from the cabin atmosphere. Interestingly, the same design features and attributes which make these systems so effective for purifying a spacecraft’s atmosphere can also make them susceptible to system upsets. Cabin conditions can be contributing causes of phenomena such as adsorbent “rollover” and catalyst poisoning can alter a system’s performance and in some instances release contamination into the cabin. Evidence of these phenomena has been observed both in flight and during ground-based tests.

The Regenerable Trace Contaminant Control System (RTCCS) is a system designed to meet all of the size, weight, power use, contaminant removal rate, and operational requirements of the International Space Station (ISS) Trace Contaminant Control Subassembly (TCCS) without the need to replace an approximately 80 lb charcoal bed every 90 days. It is designed to remove every class of contaminants found in spacecraft cabin air, including alcohols, aldehydes, aromatics, ethers, esters, chlorocarbons, halocarbons, fluorosilanes, hydrocarbons, ketones, silicones, sulfides, and inorganics, and it is designed to operate continuously with minimal maintenance or periodic replacement major components. The RTCCS is comprised primarily of a pre-sorbent bed, regenerable bed, catalyst bed subassembly, post sorbent bed, blower, and associated valves and instruments.

On June 25, 1997 a docking mishap of a Progress supply ship caused the Progress vehicle to crash into an array of solar panels and puncture the hull of the Spektr module. The puncture was small enough to allow the crew to seal off the Spektr module and repressurize the rest of the station. The Progress vehicle struck the Spektr module several times and the exact location, size, and number of punctures in the Spektr hull was unknown. Russian cosmonauts donned space suits and went inside the Spektr module to repair some electrical power cables and look for the location of the hull breach, they could not identify the exact location of the hole (or holes). The Spektr module was pressurized with Mir cabin air twice during the STS-86 fly around in an attempt to detect leakage (in the form of ice particles) from the module. Seven particles were observed within a 36 second time span, but tracking the path of the individual particles did not pinpoint a specific leak location.

Recent advances in semiconductor lasers and nonlinear optical materials permit construction of compact sensors that can measure trace air contaminants with high precision in real time, without sampling. A portable prototype sensor was built and tested in laboratory and field environments. This spectroscopic instrument measures carbon monoxide (CO) at concentrations between 0.1 and 10 ppm in air with 0.001 ppm precision, and 10-second response time. It uses 4.6-μm difference-frequency generation in periodically-poled lithium niobate (PPLN), pumped by two compact solid-state lasers. The sensor was used to measure the CO concentration profiles in chamber air during the Lunar-Mars Life Support Test Project (LMLSTP) Phase IIA test at NASA JSC. It is proposed to modify the instrument to measure several gases simultaneously, including formaldehyde. Projected use of fiber-coupled diode lasers and waveguide PPLN will permit development of a commercially viable, field-ready instrument.