Space solar power systems (SSPSs) lately planned in Japan are introduced with a result of conceptual design studies. Solar energy collected in orbit is converted into electrical energy and is transmitted to the Earth by way of microwaves or lasers. Systems of our concern are thereby Microwave-based SSPS (MSSPS) and Laser-based SSPS (LSSPS). The MSSPS basically consists of solar concentrators and a disk-like power module with I- or Y-shaped radiator. The power module is one-sidedly coated with solar cells and is internally loaded with magnetrons. The LSSPS is composed of a sun-oriented parabolic mirror and a planar radiator put on the focal line, where an array of laser devices are set up. For any of the two, system feasibilities critically depend on possibilities of size/mass reduction and heat rejection. Radiative heat transfer/exchange analyses are made considering the system thermal balance. Analysis results are written in fractional form upon the specified transmission power P. The required area A and the resulted mass M are thus simply calculated from the specific area a and the specific mass m, respectively defined as A/P and M/P. All such performance indices concerning the concentrator/mirror, the generator, the radiator, and the system are expressed in algebraic form suited to numerical computations. Empirically obtained polynomial expressions are presented to determine the cell/magnetron/laser efficiencies from the specified temperature because the system size may be highly temperature-dependent. Performance calculations have been parametrically done with various combinations of the reference temperature and the concentration ratio. Obtained numerical results are graphically shown in the figures to indicate specific system/subsystem area/mass values. Such specific values are submitted to quantitative discussion in two demonstrative design cases. Design objects are then a low-earth orbiting MSSPS of 100 kW class and a geostationary-orbiting LSSPS of 1 MW class. System feasibilities of the two are mainly examined from thermal and configurational points of view.

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