Navigation and Control According to the preliminary mission study, the requirement for the navigation and control subsystem is featured by two typical cases: a precise attitude control for astronomical observations and a moderate attitude control, capable of determination of position and velocity measurement. The basic capability of the navigation of the SFU platform will be to locate the position and determine the other dynamic characteristics by a hybrid navigation system using an inertial navigation system and the global positioning system. The standard attitude control will be made to satisfy the requirements for the sun-oriented solar array of the electrical power subsystem and the thrust vector control of an electrical propulsion experiment. The actuators for attitude control will be three-axis reaction wheels and reaction control jets. The delta-V capability of the reaction control jets is 20 m/s, which can be used for position control of the SFU platform. If guidance and position control are required, the basic SFU subsystem can support the experiment within such capability. Similarly precise attitude control will be achieved with the basic provision of the navigation and control subsystem by adding star sensors and an electronics package as a part of the experiment. 4. FLIGHT OPERATION The SFU platform will be carried by an STS orbiter to be deployed in a low Earth orbit. After it is released to become a free flyer, the mission will be carried out. After a certain period of free flight, the platform will be retrieved by the STS orbiter or one of later missions. The deployment and retrieval procedure will be the same for every type of mission. The main part of each mission between deployment and retrieval will be different depending on the mission period and extent of the crew participation in the operation and support of data management by the orbiter. The concept of deployment and retrieval operations and each mission mode will be described as follows. Deployment and Retrieval The deployment and retrieval will be performed by the STS crew with the RMS according to a normal procedure specified for the STS operation. Since there is no electrical power supply from the orbiter to the platform, an electrical activation of the SFU system will be made just after it has been taken out from the cargo bay by the RMS. Critical functional tests will be carried out while the platform is held by the RMS. The test data will be checked by the orbiter crew or relayed to the ground for check-out. The last mission operation is to deactivate the SFU platform by a command signal from the STS in operation or the ground operator. Thus the platform will be retrieved at an inactive state as required by the STS operation. Man-Tended Mission Some experiments require the STS to accompany the platform for the purpose of using the orbiter as a remote platform for an optical instrument or reference position in orbit. The orbiter will be controlled to make a formation flight with SFU. Several experiments may be carried out for a mission period as long as a week under the
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