Space station base. If the space station is used as the construction base, the SPS main structure will be constructed on the top of the space station extending upward to keep the attitude in the direction of gravity-gradient force. In this respect, vertically extended space station configuration seems to be favorable for attitude control. The space shuttle will be berthed at the lower end of the space station. According to the preliminary study, the solar cells are so bulky that they will be transported and stored in the depot on the space station in avdance. The structure elements of the SPS main structure will be assembled, whether it is prefabricated on the ground or fabricated on orbit, at the extended portion of the space station and will be moved upward to be assembled into the SPS main structure. Figure 2 shows that the antenna structure is constructed first and then the solar array structure is being constructed in parallel position with the completed antenna structure. The gimbal mechanism will connect these two large structures. The solar cell sub-array will be unwinded from the reel and deployed on the solar array structure. After completion of the total assembly, a platform will dock the SPS in order to control after it is separated and launched from the space station to a new orbit. The mass balance of the space station and the SPS will be an important factor to determine the separation procedure, since the the attitude of the space station itself might be significantly disturbed by separation. Free-flying base. If the free-flying platform is built using common subsystems of the space station, it will be provided with similar capability of the attitude and orbit control. Some preparatory works will be carried out on the space station to assemble the first fundamental structure and manipulator system to be used for assembly work later. To save the human activities on the free-flying construction base, the space station functions as a depot for the materials and components carried by the space shuttle. The structure elements such as a section of truss structure may be assembled at the space station. The transportation of them to the free-flying construction base will be performed under proper formation flight condition where the cargo escorted by an orbital maneuvering vehicle is released from the space station utilizing inertial motion of drifting backward on an orbit slightly different from that of the space station and reaches the free-flying
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