Design of Orbital Replacement Units for the Columbus Orbital Facility Condensing Heat Exchanger and Filter Assembly

A condensing heat exchanger and filter assembly (CHXFA) has been developed by SECAN/AlliedSignal under a contract from Dornier Daimler-Benz as part of a European Space Agency program. The CHXFA is part of the Environmental Control and Life Support System (ECLSS) of the Columbus Orbital Facility (COF), the European Laboratory Module of the International Space Station (ISS).

Although the COF CHXFA has a lifetime requirement of 10 years, some of the assembly components have been designated orbital replacement units (ORU's), which means that they must be designed to be replaceable “on-orbit”, in micro-gravity conditions. The CHXFA contains a filter to remove particulates from the air stream, and a differential pressure sensor to monitor pressure drop across the filter. The filter is a limited lifetime ORU, which will be periodically replaced as part of routine maintenance. The differential pressure sensor is also designated as an ORU. The assembly includes a thermal control valve (TCV) to regulate the temperature of the outlet air. The TCV is comprised of a baffle-plate flapper within a housing. The baffle position is controlled via redundant electromechanical actuators or by a manual backup. Both the electromechanical actuators and the TCV are designated ORU's.