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Manned Space Systems are usually designed to support the crew atmospheric conditions equivalent to those at sea level. In phases with frequent Extra Vehicular Activities (EVA), a reduced pressure environment is preferable to facilitate the EVA suit prebreathing procedures. The Columbus Attached Pressurised Module (APM) will face both pressure scenarios during its life. Operation at different pressure levels primarily affects the performance of the Environmental Control System (ECS) of the pressurised elements. A lower air density results in reduced heat exchange, adversely affecting both the crew comfort and the electronics air cooling. This paper reports the results of a study performed to identify the constraints and the numerous potential problem areas related to APM operations at reduced pressure. Effects of the reduced pressure on the environmental parameters have been investigated.

This paper describes the main changes affecting the APM Environmental Control System (ECS) as a consequence of the Space Station Freedom (SSF) restructuring and Columbus APM overall reconfiguration. The main purposes of this reconfiguration are: minimize the number and complexity of the interfaces with Space Station Freedom (SSF) centralize avionics command and monitoring tasks revisit the failure tolerance concept of some ECS functions unify/standardize similar functions in the two subsystem adjust lifetime requirements and simplify maintenance concept of equipment. The APM ECS consists of the following functions: active thermal control (ATCS) passive thermal control (PTCS) atmosphere pressure and composition control air revitalization and cabin ventilation temperature and humidity control vacuum and venting nitrogen supply fire detection and suppression. The new ATCS configuration provides a cooling capability for a reduced number of P/L racks by means of its moderate loop.