observations. In this paper, a preliminary SFU concept will be presented for the purpose of providing information for advanced experiments for the SEEL. 2. DESIGN FEATURES The general features of the SFU will be described well by the design requirements for the platform system. The individual items of the requirements are listed with additional short remarks in the following: Requirement 1: a free-flyer platform to be supported by the NASA Space Transportation System (STS) The SFU will be designed as a payload of the Space Shuttle orbiter to be deployed and retrieved in orbit. The flight period and type of work provided by STS will be determined by each mission. Cost reduction for STS operation will be a design driver. Requirement 2: a general-purpose facility for experiments and observation The SFU will provide experiments with electrical power, thermal control capability, pointing and positioning capability and command and data management for the payload. Any type of payload can be accommodated within the available resources, since it is designed to be a miltipurpose facility. Each mission will be planned by integration of compatible experiments and observations. Requirement 3: a single mechanical and electrical interface between the STS orbiter and on board experiments All the payloads will be fitted to the SFU structure within the limit of the STS cargo bay envelope. Electrical power will be supplied to all payloads by the electrical power subsystem of the SFU. The command and data for the pay load will be managed by the CDMS of the SFU. Requirement 4: simple integration procedures Involvement of the users in the integration work of the SFU payload should be minimized. It is most important to simplify the procedure of assembling the payload and verification of the total system from the standpoint of investigator’s participation. It is considered that the investigators pack the instruments in a unit and bring it to the integration site where work for assembling each package will be performed separately. Requirement 5: easy verification of hardware and software for reflight A conventional space system has been designed for one-time success. The SFU is one of those which will be repeatedly used for several missions. A cost-effective approach to verification of hardware for reflight will be a crucial factor of this system. Selection of materials and structure design is an example of difference of the SFU design requirement from conventional space systems. Requirement 6: future capability Considering that the space station system consists of multiple spacecraft, the SFU is expected to be one of the spacecraft operated under the support of the space
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