Boeing is responsible for Space Station Freedom (Work Package (WP) 01) which includes the Habitat and U.S. Laboratory modules, which includes the integration of the Environmental Control and Life Support System (ECLSS). Included as part of the ECLSS is the Atmosphere Revitalization (AR) subsystem. The AR subsystem provides for removal of metabolic carbon dioxide, removal of trace contaminants, and continuous monitoring of the cabin atmosphere major constituent composition during the Manned Tended Configuration (MTC) phase of station operations. The focus of this paper is on the Carbon Dioxide Removal Assembly (CDRA) flight design aspects of the Space Station Freedom (SSF) AR subsystem.
A Four Bed Molecular Sieve (4BMS) has been selected by Boeing as the CDRA for SSF. The CDRA removes carbon dioxide from an air slip stream pulled from the Cabin Air Temperature & Humidity Control (THC) assembly. The carbon dioxide is then desorbed to space vacuum using thermal/pressure swing methodology. Carbon dioxide will be removed at a rate equal to the time averaged carbon dioxide generation rate of the crew members.
The CDRA operates cyclically using me four beds to achieve a continuous removal process with simultaneous adsorption and regeneration of desiccant beds and carbon dioxide adsorbent beds. The 4BMS design is completely regenerative and has no scheduled maintenance requirements during the entire MTC phase of station operations.
To date 4BMS technology has been used in four generations of development testing. They are the NASA Core Module Integration System (CMIS), the Boeing Comparative Test, the Boeing Pre-development Operational Systems Test (POST), (1) and Subcontractor testing at AlliedSignal. The molecular sieve material has also successfully operated during the entire Skylab program removing carbon dioxide and humidity from the Skylab habitable atmosphere (2).
SSF is being designed for a crew of four astronauts with scarring in place for a closed loop AR, and to allow growth to the Eight Man Crew Capability (EMCC) configuration. The carbon dioxide removal function must remove experiment animal carbon dioxide at EMCC as well as crew metabolic carbon dioxide and store it for subsequent conversion in the closed loop AR carbon dioxide reduction system.
The MTC CDRA Normal mode of operation will remove 0.17 kg/hr of carbon dioxide (nominal 4-person generation rate) with an inlet carbon dioxide partial pressure of 3.0 mm Hg and a cabin pressure of 99.9-104.8 kPa. The CDRA has the ability to adjust the removal rate by +/-10% resulting in an effective range of 0.15 to 0.19 kg/hr.
The MTC CDRA Degraded mode of operation will remove 0.33 kg/hr of carbon dioxide (nominal 8-person generation rate) with an inlet carbon dioxide partial pressure of 6.0 mm Hg and a cabin pressure of 99.9-104.8 kPa. The Degraded mode also has the capacity to effective range of 0.30 - 0.36 kg/hr.
This paper will discuss the technology and operation of the MTC open loop CDRA, its functional interfaces within AR, ECLSS, and SSF, scars for growth to the closed loop CDRA operation, and specific performance attributes of the flight hardware design that is expected to be launched with the U.S. Laboratory A module on Mission Build (MB) flight six in 1996.