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The requirements related to the thermal control of HERMES space-plane suggest the utilization of technical solutions based on active and passive techniques. The configuration of the space-vehicle with pressurized and unpressurized compartments presents a variety of different problems, which generally require dedicated solutions. The complex mission profile include atmospheric and orbital conditions, with several phases and modes of operation (free-flying and docked). The extremely wide range of environmental conditions, together with the timeline of internal power dissipations requires the adoption of a particularly flexible thermal control. The ATCS (Active Thermal Control Section) mainly relies on the capability of water and Freon 114 fluid cooling loops. They collect waste heat from the sources located inside the compartments and transport this power to the available rejection devices.

This paper gives an overview of the Vacuum and Venting Subsystem architecture of COLUMBUS Pressurised Modules, summarises the Subsystem's requirements and discusses the baseline design solutions at loop and component level. The Vacuum and Venting Subsystem architecture mainly consists of: Module internal loops collecting waste gases evacuated from directly interfacing Payloads (P/Ls) Space Station Freedom (SSF) based waste gas bus, providing removal and disposal of docked element vacuum loop waste gases Dumping nozzles to exhaust the collected gases towards deep space without generation of dynamic actions Loop control and monitoring functions provided by on/off valves and pressure sensors interfacing with an intelligent control unit Heaters and temperature sensors for thermal control of dumping nozzles in order to limit heat leaks.

Air cooling of the avionics units (Subsystem equipment and Payloads) of the Columbus Pressurised Modules (PM) is performed via avionics loops, providing heat collection from dedicated racks and rejecting the collected heat load by means of an avionics heat exchanger (AHX). An overview of possible rack architectures, air loop accommodations and control solutions which are candidates for the Columbus PMs is presented. The system requirements have been assessed as a starting point, in order to define the requested capabilities and the constraints that the design of the rack and the loop has to fulfil. In particular, the architectures of the European single and double rack and of the U.S. double rack in Space Station Freedom (SSF) have been compared and the relevant options of accommodation in the avionics loops and functional interfaces have been investigated.