We will only briefly identify some of the issues here, without attempting to detail all of the possible approaches, and suggest some development steps required. The issues involved with providing a reference clock signal and distributing the proper phase signal to a non-rigid array have been only superficially addressed. This could be done either with analog processing or with digital circuitry. The difficulty of this problem is decreased if significant amounts of integrated processing capability is available at low cost. If the elements are equipped with local oscillators, then the phase signal is only required to keep the local oscillators in correct phase. If the system does not have local oscillators, or if the local oscillators have poor frequency stability, a continuous phase signal is needed. A full design of the microwave antenna and its integration with the RF generator and solar cell including such issues as backplane construction needs to be performed. Antenna elements have radiation patterns that yield best efficiency at a given angle. Off-angle losses and polarization issues need to be addressed. Solid-state RF generation technology issues will need to be addressed in order to verify that manufacturable devices can meet the efficiency and reliability goals required for a SPS. In general, the problem areas appear amenable to technology and engineering solutions. The important question is whether resolution of the problem areas would unacceptably increase the complexity, weight, or cost of the system. To this end system analysis needs to be performed to determine the technical and economic feasibility of the concept. If feasible, design, development and demonstration of the integrated solar cel/transmitter/antenna building blocks, possibly as a self powered RF repeater, should be undertaken. Finally integration of the building blocks and other support systems into a flight demonstration/ and or first application could lay the groundwork for low mass space power by use of integrated solar power satellites. Conclusions Thin-film photovoltaic arrays, microwave solid-state devices, and increasing computational technology have the potential to create a revolutionary change in solar power satellite design, with possible improvements in power to weight ratio of a factor of ten to a hundred. Thin-film photovoltaics alone could yield a notable improvement in mass; however, to take full advantage of the technologies being developed, we have proposed a design for a fully integrated photovoltaic/microwave system, where the phased array microwave elements are integrated with the solar cells, eliminating all the power management and distribution, reducing the waste thermal management subsystem, and eliminating a separate discrete antenna. To take advantage of this design, small self powered transmitter “building blocks” will need to be designed, developed and tested. Further, the control of these elements and their integration in a light weight structure will need to be performed. If this could be done, many new applications, especially those with small receivers at multiple
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