experiment phase, orbit transfer phase and GEO experiment phase. The total operation period is about three and a half years. LEO experiment phase. The first phase will be started with test run of individual subsystems. The first test is functional test of attitude control which is concerned with the control for sun orientation of solar array and antenna pointing. Aerodynamic drag force acting on the SPS will be measured at various attitudes. The second and third tests are power generation tests under the load-free condition and electrical propulsion operation respectively. Finally in this phase a power transmission test on LEO will be conducted. Orbit transfer phase. The electrical propulsion will be operated to raise the orbit. Mean while microwave transmission test can be conducted interupting the electrical propulsion operation. This phase will be ended by insertion of the SPS into a GEO. GEO experiment phase. The additional construction work for the antenna will be performed after SPS is placed on the GEO. The Ga-As solar cell array will be fabricated with the new MBGE method, which is expected to increase the total power output up to 30MW. The power generation test will follow the fabrication. Then the microwave power transmission test on GEO will be conducted with the uprated antenna and solar power generator. The general concept of the SPS is shown by Fig. 1. The antenna structure with the diagonal length of 400 m which is partially used for the antenna array for microwave transmission test on LEO, is constructed for investigation of a dynamic behavior of large structure beforehand. ADPTATION FOR SPACE STATION MISSION Since the concept of space station is taking a shape, it is possible to some extent to reexamine the concept of the 10 MW SPS in the context of the space station mission. There are two important factors to be considered. One is concerned with the cost of the project. For example, the original concept of the 10 MW SPS has been assumed to have a construction base specially designed and exclusively used for this project. If it is replaced by services of the space station, the operation cost may be reduced. The other one is accumulated experience of the preceding missions which may include many related experiments. If results of these experiments are applied for the 10 MW SPS, it would be beneficial to both parties. In this section, several points of modification of the original concept are discussed. Possible Operation To take advantage of services provided by the space station, the procedure of the first construction phase will be significantly changed. The space station itself or a co-orbiting platform will be used for the construction base which is to be launched first to install special construction facility. If the 10 MW SPS is constructed on the space station, the main facility and working space will be occupied by this mission. Considering that the mass of the mission equals to fifteen to twenty flights of STS, the attitude control and resources management of the space station will be significantly affected by this mission. Another method of using a co-orbiting free-flyer seems to solve this problem. The construction materials will be delivered to the space station where they are processed to make structure elements. Then they are passed to the coorbiting free-flying platform where main assembly work will be performed. Some ideas are described for each.
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