Columbus APM Environmental Control System Overview: Space Station and APM Restructuring Consequences

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:

1. active thermal control (ATCS)
2. passive thermal control (PTCS)
3. atmosphere pressure and composition control
4. air revitalization and cabin ventilation
5. temperature and humidity control
6. vacuum and venting
7. nitrogen supply
8. 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. No modification is envisaged on the low temperature loop. Failure cases on both SSF thermal buses and APM ATCS have been considered and assessed, resulting in an optimization of the ATCS operation in off-nominal modes. Due to the adoption of a new APM launcher (ARIANE 5) instead of NSTS, the Negative Pressure Relief function is no longer required. A new cabin loop architecture is considered based on the use of three fans for air distribution in the APM thermal conditioning and air exchange with the adjacent SSF node (Intermodule Ventilation). As far as the Vacuum and Venting system is concerned, the only changes are the reduction of the connected lateral P/L racks and the deletion of the venting interface with the SSF. The same lateral P/L racks are also connected to the Nitrogen Supply system with the deletion of the relevant interface valves. The main change in the Fire Detection system concerns the new location of smoke detectors within the cabin loop. The Fire Suppression system is impacted due to the reduction of the number of enclosures requiring a fire suppression capability. Optimization in heater control has been achieved, while the decentralized valve control concept has been deleted in favour of a centralized one via Power Distribution Unit (PDU).