determine performance stability and lifetimes of the various photovoltaic array concepts. The working group recommended efforts to demonstrate a 25% efficient AMO thin film cascade solar cell and show a potential for 35% efficiency. Also alternative concepts leading to 50% conversion efficiency should be pursued because of the enormous advantages to increasing photovoltaic efficiency, thereby reducing the size and weight of the array. Other major issues are cell encapsulation and blanket integration. The geometry of the blanket submodules, very thin and very large, requires new approaches and innovative techniques for fabrication. There are a variety of solar-thermal options that have been investigated as possible alternatives to photovoltaic conversion. The advantages of solar thermal systems include insensitivity to radiation effects, simpler power conditioning, and the potential for high efficiency. Concern was expressed that the current overwhelming emphasis on the photovoltaic approach could lead to insufficient examination of promising solar-thermal options. Energy conversion systems considered included Brayton, potassium Rankine, cesium/steam, organic Rankine, and thermionic cycles. Concentrators included parabolic dishes, compound parabolic concentrators, faceted reflectors, cassegranian concentrators, low concentration planar reflectors and inflated structures. Both heat pipe and tube-fm radiators were considered. It was concluded that all the concepts require substantial advances in technology in order that the goals set for SPS might be achieved. Because of this, none of the concepts has such low risk that it can be relied upon to the exclusion of the others. Extremely high reliability can be achieved for solar thermal systems by the use of frictionless bearings (gas bearings) for rotating equipment and a large number of redundant powergeneration modules. The economic practicality of the SPS is also greatly affected by the power distribution and management subsystem which directs the electric power output from the solar array modules to the microwave antenna. The efficiency of the power distribution and processing subsystem is also critical through its impact on total SPS weight. The technical feasibility of the SPS will depend in part on the technology readiness of techniques, components, and equipment to reliably distribute, process, and interrupt hundreds of megawatts of power at tens of thousands of kilovolts. The problems of heat dissipation and prevention of breakdowns due to corona discharge or arc-overs are much more severe in the space environment, because of the absence of the insulating and thermal transfer properties of air. The total weight of the Satellite Power System is projected to be between 35-50 million kg for a 5 GW system. This corresponds to a specific power density of around 5 or 6 kg/kW of power delivered to the antenna. However present aerospace power processing technology corresponds to a power density of 10-15 kg/kW. Thus the power processing alone, using present technology, weighs more than the total projected system. In addition, present technology will not perform the functions required. Therefore a major effort must be made in power processing technology development to make future power satellite systems technically feasible and economically viable. One major concern is the successful realization of high power kilovolt protection switches which are wired to protect the transmission tubes within microseconds of normally occurring arcs. Considerable work remains to be done on switchgear, power electronic devices, power transmission elements, and rotary joints. The geostationery orbit plasma environment presents special hazards to spacecraft designers because of the presence of a dense, high temperature plasma associated with the plasma sheet. Plasma sheet electrons may charge the satellite to high
RkJQdWJsaXNoZXIy MTU5NjU0Mg==