Fig. 4. Communication link for platform. The possible formation flight configurations are: [1] Separate flight in co-orbiting condition; [2] Slightly different orbital plane operation; [3] Diamond Loop Operation; [4] Eccentricity enhancement operation; 15] Orbit raising operation. The first two will be utilized for plasma and beam monitor, and the rest will be applied for thrust measurement of the test thrusters. As for communication and tracking requirement, the space station is a primary communication node for the experiment carried out onboard the platform as stated. The data stream, therefore, is transferred to the ground-based control center via the space station. The general communication network is depicted in Fig. 4. The exceptional cases, however, appear in the operation using subsatellites. The traffic control near the space station is also handled by the space station. The tracking of the objects flying in its proximity is done by the Global Positioning System (GPS) as well as the radar system onboard the space station. The platform is regarded to have a support of the GPS. The flow of the tracking data is depicted in Fig. 5. An additional link is necessary for the subsatellite operation. The tracking and traffic control may be more complicated when the STS comes in vicinity of the space station. EVOLUTIONARY PLAN The operations of SEEL missions are planned in the time phased manner as shown in Fig. 6. The order of mission operation is matched with that of facility construction. As a main facility of SEEL, the bus platform is built at first, and will be in operation from the start of the space station. Since SPEX and APT experiments can be executed only by the provision of bus platform, they go first. If a subsatellite is added to the bus platform, SRADAR experiment can be operated. The subsatellite is a target for the calibration of radar range finder. Finally after these missions, a
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