The European Space Agency's Eureca (European retrievable carrier) is the first custom-built spacecraft designed for prolonged research into materials and organisms under microgravity ('weightless') conditions. It also carries a variety of instruments to sense the space environment. The 4.5-tonne spacecraft began its first mission (Eureca 1) on August 1, 1992, when it was deployed from the payload bay of shuttle orbiter Atlantis on STS-46. Placed initially in a 425-km orbit, Eureca fired on-board thrusters to raise it to its operational orbit of 515 km. Its retrieval from orbit, again by Atlantis, was scheduled for June 1993. The Eureca structure is made of high-strength carbon-fibre struts and titanium nodal points, joined together to form a framework of cubic elements. Thermal control is provided by a combination of heaters, circulation of refrigerant, radiators and blanket insulation, depending on the thermal load of the various experimental units. Electrical power to run the spacecraft systems, instruments and communications is provided by two panels of solar cells, which generate some 5,000 watts. Sets of thrusters powered by hydrazine are fired to transfer the spacecraft to and from its operational orbit. In space Eureca is under the control of the operations control centre (OCC) at ESA's European Space Operations Centre (ESOC) in Darmstadt, Germany. Communications to it are channelled through ground stations at Maspalomas in the Canary Islands and at Kourou (ESA's main launch site) in French Guiana, South America. In its low Earth orbit, Eureca is 'visible' to these stations as far as communications are concerned for only about 3 per cent of the time. Most operations on Eureca are therefore conducted in automatic mode. With its 16 megabyte on-board memory, Eureca can receive at each station pass up to 1,000 commands for operations to be carried out before the next pass. And at each pass, the on-board recorders transmit experimental data they have collected since the last one. The OCC is in charge of scheduling operations on Eureca, allocating the needs of each experiment in terms of power supply and time. To help experimenters plan their operations, a microgravity user support centre has been set up at the German Space Research Centre (DLR) at Porz-Wahn near Cologne. Over 50 experiments were flown on Eureca 1, involving 15 separate facilities. They were the automatic mirror furnace (Ger), solution growth facility (Belg), protein crystallization facility (Ger), multifurnace assembly (Ital), exobiology and radiation assembly (Ger), high-precision thermostat (Ger, Ital), solar spectrum instrument (Fr), solar constant and variability instrument (Belg), occultation radiometer (Belg), wide-angle telescope (Den), timeband capture cell experiment (UK), radio frequency ion thruster assembly (Ger), inter-orbit communication instrument (Fr, Neth) and advanced solar gallium arsenide array (Ital). The names of the facilities reflect the broad range of Eureca investigations. Experiments with the inter-orbit communication instrument should pave the way for better real-time data transmission via, on the Eureca 1 mission, the Olympus communications satellite, and on later ones purpose-built data relay satellites.
