Columbus Active Thermal Control Equipment Development

The Columbus laboratory module for the International Space Station (ISS) uses active thermal control for cooling of avionics and payload in the pressurized compartment. The Active Thermal Control Subsystem (ATCS) is based on a water loop rejecting waste heat to the Medium Temperature Heat Exchanger and Low Temperature Heat Exchanger on Node 2, part of the US Segment of the ISS. Flow and temperature control in the ATCS is achieved by means of the Water Pump Assembly (WPA) and the 3-Way Modulating Valve (WTMO) units. For the flow control the WPA speed is commanded so that a fixed pressure drop is maintained over the plenum with the avionics and payload branches. Adjusting the WTMO internal flow split permit the two active units to perform the CHX and plenum inlet temperature control. The WPA includes a filter and an accumulator to control the pressure in the ATCS and to compensate for leakage and temperature-dependent volume variations. A gas trap will be inserted into the loop at the WPA interface for the event that bubbles have to be vented from the ATCS water. The ATCS loop redundancy is implemented by the use of two sets each consisting of one WPA unit and two WTMO units. For maintenance or in the event of failure it is possible to re-configure to the redundant units without the need to interrupt Columbus operations. The purpose is to present the design and the analytical and test activities which have culminated in qualification and acceptance of the equipment. An example of the challenges, which had to be faced in the course of the development and verification, is the gas trap. Surfacing difficulties with the automatically operated membrane type unit have forced a re-orientation towards a manually operated hydrocyclone-based design.