construction base. The manipulator will be able to catch the cargo approaching at a very small relative velocity. The structure elements delivered will be used to extend the back bone of the free-flyer to increase the gravity-gradient stability. In this case, tools and equipments for assembly works have to be carried on the platform beforehand. Anticipated Results of Preceding Missions There are many technologies which will have been tested, when this mission is started. The Japanese mission items put in the mission data base contains the following items which are concerned with energy, structure, robotics and space operations. The missions proposed by the participating nations of the space station program would contain similar missions. It is difficult at the present to predict how many of these will be implemented but the list will give a good estimation of the technologies available prior to the start of the SPS experiment project. It is expected that some of the missions will be repeated in a larger scale by participating in the 10 MW SPS project. ENHANCEMENT OF SELLING POINTS As shown above this space station mission is a specially large project which has to share the precious resourses with other candidate projects. Therefore it is most important to pay large effort to identify the values of the project which can justify the large amount of expense. But the original concept, however, is mainly concerned with engineering and technological aspects of the SPS. It is necessary to reexamine the objectves of the project not only from the viewpoint of SPS development but also benefits of many related activities. This approach will be typical case of implementation of the Terracing of space projects indicated by Glaser(1983). Several items which are considered to enhance the merit of the project are listed as follows. Follow-on mission The technologies to be used for this project will be obtained through the earlier phase of the space station operation. As the result of such missions, new research areas will be opened. Some experiments will require more extensive study with a system of larger scale. The 10 MW SPS will provide these experiments with opportunities to be applied in a large scale of practical use or to continue extensive study using the SPS hardware as a test bed. Cost reduction It has been suggested that the space station will play an important role of reducing the project
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