Fig. 21. Multifunction communications platform necessary construction functions such as the deployment and attachment of solar arrays to the basic structure (Fig. 20). Two orbital locations for the primary construction activities in space have been studied. Construction in the geostationary orbit offers the advantage of continuous sunlight, which decreases the differential thermal effects on the structure during construction and reduces the need for artificial illumination of the workplace. Additionally, the construction process can be designed to produce the satellite in its final operational form, eliminating a module berthing operation. Finally, it avoids the requirement to transfer the large system from low Earth orbit to geosynchronous orbit. The low-Earth-orbit approach, however, does provide the advantage of operating in close proximity to Earth and shares, with Earth, the protection from space radiation provided by the trapped radiation (Van Allen) belt. Gravitational attraction varies with altitude, so that very low Earth orbit must overcome relatively large gravity gradient torques during construction and transit. To lessen these torques, the satellite could be constructed in low Earth orbit in modules, with final joining or berthing of the modules at the geostationary operational orbit. The number of persons involved in the construction process is a function of the degree of automation employed. The size of the construction crew also depends on the amount of maintenance the construction equipment will require. Present estimates are that about 500 persons, including support personnel, will be needed in orbit to support construction at the rate of two 5000-MW satellites of new capacity per year. Contrary to intuitive impressions, cost analyses have indicated that the Solar Power Satellite system cost is relatively insensitive to crew size in space. Construction activities in space lead to the need for protecting personnel from the natural environmental hazards. Provisions for a life-supporting atmosphere and protection from solar thermal and ultraviolet radiation are well-understood engineering problems. Protection from energetic particle fluxes requires that more knowledge be gained on the expected dynamic range of these phenomena so that engineering measures to shield space workers can be accomplished. Exposure standards must also be established to determine the necessary protective measures. The extremely large size but very-low-density characteristics of the satellite require that it be constructed in space, or “onsite.” It is anticipated that other programs of the future will also require satellites of a size that will require construction
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