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This paper presents some of the important aspects of the development work carried out recently in the Hermes ECLSS (since Ref. 1). For various constituent hardware items of the ECLSS, the paper describes and explains the technical constraints which are at the origin of the development work, discusses the design concepts which have been identified and investigated to fulfill the constraints, and presents the technical solution which has been selected. For some hardware items (e.g. cabin fan, toilet assembly), for which the initial design selection has been supported by breadboard tests, the paper presents the rationale behind such tests and the major test results obtained. The consequences derived from the test experience for the further development work are explained.

Electroemissive (ESTHER) devices are thin sheets - similar to solar cells - whose infrared emissivity can be varied reversibly by electrical charging. Bonded to the external surfaces of spacecraft radiators they can be used for the active control of the Irradiated heat by consuming negligible electrical energy. The window to a revolutionary new thermal control design technology for spacecraft may be opened.

The pressurized modules use water and air coolant circuits to remove the dissipated heat from the sources and to transport it to the heat sink. The advantage of the water loops is to provide a high heat removal capability at low power consumption well suited for high specific heat loads i.e. assemblies with high dissipation and small volume. Air coolant circuits offer a higher flexibility to account for different shapes of the equipments and for changes in the configuration of the loop. Thus they are better suited for assemblies with lower dissipation and do not impose as much design restrictions on assemblies as water loops. But they have a higher specific power demand compared to water loops. In the Columbus pressurized modules avionics air loops and cabin air loops are installed. Both of them belong to the Environmental and Life Support Subsystem (ECLSS).

The redesign of the international Space Station Freedom (SSF) and funding constraints in the ESA member states caused a redirection of the development effort for the Attached Pressurised Module (APM). For the ECLSS the most important changes are the reduction in length of the module in order to make it compatible with the ARIANE V capabilities and the more severe cost constraints. As a result new concepts for the cabin loop were investigated leading to a decrease in cabin loop power consumption, mass and volume and a reduced development effort due to a lower number of items. In the previous concept a module internal loop with a flow rate of 864m3/hr and an Intermodule Ventilation (IMV) flow rate for air revitalisation to the station with 240m3/hr were installed. The revised boundary conditions with a reduced overall massflow rate of 540m3/hr allows the combination of the cabin loop and the IMV with limited impact on the total power consumption.

Electro emissive devices, called ESTHER, are thin sheets - similar to solar cells - whose infrared emissivity can be varied reversibely by electrical charging. Bonded to external surfaces of spacecraft radiators, they allow active control of the heat radiated to space while consuming negligible electrical energy. Applying this novel component for spacecraft thermal control, considerable cost savings in spacecraft development and operation can be achieved. Progress in the design and manufacturing process has been made since the first puplication in July '92 /1/ revealing an increased variability of emissivity and an increased duty cycle stability. The material selection process was facilitated by the exposure of material samples to the space environment during two spaceflight missions and the subsequent material analyses.

On behalf of the German Space Agency, DARA, the Spacelab facility NIZEMI (Slow Rotating Centrifuge Microscope) was developed for IML-2 mission in July 1994. The facility permits the investigation of samples under various levels of acceleration. Primary utilization of the facility during the IML-2 mission is for the investigation of samples in the field of gravitational biology. For observation purposes two optical units, a microscope and a macroscope, and the infrastructure for thermal control of the samples has been installed on a centrifuge turntable. The acceleration can be adjusted at levels between 10-3 g and 1.5 g. The rotating centrifuge itself and several moveable items like fans and stages, which are attached on the centrifuge turntable, may affect the microgravity environment of Spacelab. The equipment accommodated on the centrifuge turntable does not allow a design for a uniform mass distribution. Resulting unbalances must be compensated by suitable balancing weights.