Station FREEDOM. The first cornerstone is the Solar Terrestrial Science Program. The STSP consists of the SOHO solar observatory and a cluster mission of four spacecraft to study the Earth's plasma environment beginning in 1996. The second cornerstone is the X-ray Multi-mirror mission (XMM), a major astronomy facility to be launched in 1998. The third cornerstone is ROSETTA, an ambitious comet nucleus sample return mission. The fourth is FIRST, a very large instrument far infrared astronomy mission. Both XMM and FIRST will be launched after 2000. 3. European Spacecraft Power Requirements There was a dramatic growth in the electrical power requirements for European space missions in the 1980's. There has also been a need to provide an increasing fraction of the total spacecraft power to the mission payload instead of to spacecraft housekeeping. For example, this kind of power requirements growth for ESA developed spacecraft is evident in: - LEO applications, where early scientific missions needing a few hundred watts have given way to requirements of a few kilowatts being considered for HERMES and COLUMBUS. - Geosynchronous applications, where telecommunications developments have moved steadily from the 800 watts needed by the ECS satellite family of the early 1980's to the 7 kilowatt requirementsof the current OLYMPUS programme.
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