active microgravity or materials science experiments on the free flying laboratory. The COLUMBUS polar platform power supply design is currently under review. After careful spacecraft level trade studies and design evaluations, either the COLUMBUS resource module approach or the approach to be used on ERS-1 will be chosen. Both of these approaches have been described above. The COLUMBUS polar platform is currently assumed to need 4 kilowatts for the Earth monitoring systems, leading to a solar array size of 7 to 10 kilowatts. Typical instruments are imaging radars, radiometers, etc. 3.1.1.4 HERMES The proposed HERMES spaceplane will bring a crew of three to LEO. HERMES will use dual fuel cells for primary energy production, with backup and peaking capacity provided by dual lithium primary batteries. The average power demand on the HERMES power supply system will be 3 to 4 kilowatts. Peak power demands will be three to four times as high. These peak power demands will occur during critical mission periods such as vehicle re-entry. Power is distributed by four independent power control and distribution units. These transfer power between the various different energy sources and the four DC power busses. Methods of interconnecting HERMES and the manned COLUMBUS elements for the interchange of up to 4 kilowatts of electricity is being considered during the design definition phase of these two programs. The energy and power requirements for the manipulator arm and space suit associated with HERMES are also being considered during HERMES design definition. 3.1.2 Power System Requirements for GEO Missions Due to ESA support and encouragement in the 1970's, the European aerospace industry now regularly competes in the international telecommunication satellite market. European industry has successfully supplied geostationary spacecraft systems for both national customers and international organizations. The ESA is currently focussing its efforts in geostationary satellite technology on high power direct television broadcasting communications satellites through the OLYMPUS programme. 3.1.2.1 OLYMPUS OLYMPUS-1 is a three axis stabilized geostationary communications spacecraft. The basic power system is configured to provide 3.5 kilowatts in sunlight and 1.6 kilowatts during eclipse. This basic configuration is flexible enough that minor modification could provide 7 kilowatts in sunlight and 500 watts in eclipse - suitable for use as a direct broadcast television satellite, or it could provide 3.5 kilowatts in both sunlight and eclipse, suitable for general telecommunications usage.
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