Expose
Introduction
EXPOSE is the third facility dedicated to exobiology built by ESA; it follows the positive experiences of EURECA-ERA (1992-93) and of BIOPAN (1993, 97, 99), the pan-shaped container designed for the Russian retrievable capsule FOTON and still in service. Four short-term flights (two weeks) have been successfully performed so far with FOTON, and a valuable amount of scientific data has been obtained. Two more BIOPAN missions are foreseen in 2005 and 2006.
EXPOSE instead has been developed for medium- long term flights on the International Space Station. The facility is conceived to allow exposure of biological specimen and material samples whilst recording data on temperature and radiation spectra. It will be mounted on one of the four external balconies of the Columbus module, on the ISS.
Facility Description
The EXPOSE assembly includes the facility and its supporting structure, interfacing with the EUTEF-CEPA (Columbus External Platform Adapter). The facility provides common functionalities, services and a controlled environment to the experiment samples (e.g. shutters, scientific and housekeeping data acquisition and transmission, thermal control). The facility includes the following subsystems:
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Structure and mechanisms;
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Shutters (incl. lids, hinges, shutter drives);
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Trays (incl. windows, seals, valves, connectors);
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Sample carriers (incl. windows, filters, controls);
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ECU (EXPOSE Control Unit: motor and valves control, data acquisition);
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Sensors (temperature, pressure, UV, proximity); 4 sensors packages (UVB + radiometer) are positioned on the 4 facility corners;
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TCS (Thermal Control System), based on heaters, MLI, coatings;
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Electrical I/F to EUTEF Data Handling and Power Unit (DHPU).
Mechanical I/F to EUTEF-CEPA (I/F Bracket)
The EXPOSE actuators are controlled by software via the ECU micro controller; they can also be operated via the TM/TC link. In particular, the micro controller provides the following functions:
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Acquisition and transmission of housekeeping, temperature (8x) & solar sensors (5x) data;
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Acquisition and transmission of R3D data;
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Data storage (in case of data link interruption);
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Command and control of 3 motor driven lids (shutters) by stepper motors;
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Command and control of 3 motor driven valves for vented experiment compartments;
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Thermal control of experiments, achieved with 2 different set of heaters, thermostat controlled, positioned underneath each experiment tray and on the inner side of the facility frame.
Overheat protection, by automatic lid closure whenever a predefined temperature is exceeded
Experiment Hardware
The three experiment trays are supporting and sealing structures for the scientific payload. They are equipped with four squared recesses, 77 x 77 x 26 mm each, where the sample carriers are inserted. These are lightweight elements provided with a number of sample cells, whose quantity, geometry and characteristics depend on the experiment typology.
Each tray host then four carriers, sealed with optical windows or left open to the space environment. The trays have a mechanical interface to the structure and comply with the design of the shutters. Their configuration allows a free field of view for the sample carriers (no shade from rim or other protruding elements).
The trays are electrically connected to the structure by matable/dematable connectors.