Main Structure and Construction Base The main structure consists of solar array and antenna structures. The original choice of structure is truss structure of beam elements made of carbon fiber reinforced polyalfone resin. The solar array structure is 600 m long, 400 m wide and 85 m high, assembled of modular block, of truss structure, whose size is 100 m x 100 m x 85 m. Two types of beam are basic structure elements. One has triangular cross-section with the width of 1.5 m and the length is 100 m. The other is square cross-sectional beam with the width of 2 m and the length of 85 m. The beams will be fabricated with automatic beam builders on the orbital construction base. The antenna truss structure is made of the triangular beams only. The main structure will be made at the special construction base orbiting at the height of 500 km. A movable rotating crane installed on the base and a teleoperator will be used for assembling the beams into the structure. The first two solar array blocks are made and attached to the construction base and other blocks will be constructed one by one. Solar Array There are two different types of solar array assumed to be used for this project. During the construction phase in a low earth orbit, the first 10 MW solar array consisting of 50 units of flexible solar sub-array which generate 200 kW each. The sub-array is to be rolled in a size of 1.42 diameter and the width of 12 m. The weight of each roll is 300 kg. Thus the total weight of the solar cell will be 15 t, but only seven rolls can be carried by a single flight of STS due to the volume limitation of the cargo bay. The second type of solar array which is fabricated by the method of molecular beam grapho-epitaxy (MBGE) will be constructed in a geostationary orbit, to take advantage of the high vacuum environment. Purpose of this construction is to verify the method as an alternate of the first method. The concept of the MBGE manufacturing is not well defined in terms of mission requirements yet. Microwave System The experiment of microwave transmission test is assumed to be conducted on a low earth orbit (LEO) and geostationary orbit(GEO). The antenna to be used on LEO is as large as 100 m in diameter, while the antenna diameter of 1000 m is required for the test from GEO. Since the antenna assembly is a phased array antenna, it is possible to change the configuration of the initial antenna by additional construction work which is planned. The microwave device being studied is klystron, magnetron and GaAs FET (Field Effect Transistor). The choice of the device will depend on the progress of each technology in the coming decade. Power Control Even at the beginning of the next century, it would be a difficult technical problem to handle an electrical power as high as 10 MW in space. One of the problems is the mass required for electrical wiring on the SPS. The system proposed for the 10 MW SPS is a cryogenic power distribution system. For a cryogenic system, the space environment is considered to be better than the terrestrial one. The power required for the cryogenic system is approximately 31 kW and the radiator area is 900 m , when the solar array output power voltage is 4 kV and the electrical current is 5 kA. A significant mass saving can be accomplished with this system compared with an ordinary temperature system. Robotics For construction and maintenace of the cryogenic system, manipulators or space robots are required. The works to be done by the robot will be assembling superconducting cable, setting terminals and refrigerators cabling work, cool-down management and maintenance during operation. The space robots required for this system will be designed to satisfy general requirements including these functions and other uses. Electrical Propulsion After the SPS is constructed and partly tested on LEO, it will be transferred to a geosynchronous orbit with electrical propulsion utilizing the electrical power generated on the SPS. The technology of MPD arcjet is well developed and will satisfy the required performance. The available specific impulse ranges from 2000 sec to 8000 sec, which covers the range to minimize the propellant consumption. The MPD arcjet thruster is characterized by the relatively high thrust density, which make the size of thruster smaller than ion propulsion. The total number of the thruster is 120. Each thruster consumes an electrical power of 83 kW in average. They are assembled in six clusters consisting 20 thruster units for each. Only one unit of thruster for each cluster is fired for 50 msec and switched to the next one. Thus each thruster operates one cycle in a second and the total power consumption is 10 MW. The propellant can be chosen from various materials, such as hydrogen, helium, methane, ammonia, neon, nitrogen, argon and others, which have been tested in laboratory. If the environmetal issue is included in this test, several propellant species will be tested. Operation Test operation after completion of the 10 MW SPS on LEO can be divided into three phases; LEO
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