Actually-Practical Orbital Solar Power

It is common to make fun of orbital solar power projects, for good reasons. Management consulting companies love getting asked to analyze orbital solar, because they get to dust off the same takedown as last time and sell it again.

Problems with orbital power designs include poor efficiency converting sunshine, in place, to electrical power to drive the microwave antenna array to beam power to rectennas on the ground; huge expense to loft big arrays of heavy solar panels to orbit; and scaremongering about microwaves from space affecting wildlife. To be useful at all, such orbital arrays would need to be very large to drive a microwave antenna array broad enough to focus its beam tightly to drive a practical rectenna array on the ground. And they would need huge, dedicated, otherwise useless rectenna arrays.

But I haven't seen a proposal like this one.

You need some background information to follow this, some of it obvious, some less so. First, stacking microscopically thin layers of transparent material of differing refractive indices six or seven deep makes a super-lightweight mirror that reflects only one or a few wavelengths of light, letting the rest pass through. Second, a laser tube can be pumped by monochromatic light coming in from all sides. Third, terrestrial solar farms illuminated with monochromatic laser light can convert it to electrical power at radically higher efficiency than they can blackbody sunshine. Fourth, a laser beam operating at an optical wavelength with intensity at ground level no greater than sunshine creates no risks to the public or wildlife. Fifth, existing solar farms sit idle at night; but even in the daytime, they could produce more power given more input illumination.

If the orbital arrays to collect solar radiation are mostly just extremely light mirrors, and no conversion to electrical power occurs in orbit because the light they collect directly pumps a laser tube, mass and efficiency problems are eliminated. Even a relatively small satellite would be useful, as the laser does not need to be large to achieve good focus. Each unit, of whatever size, may collect and beam its power independently. And, no dedicated receiver is needed; any existing solar farm the laser points at converts the delivered illumination. And, no one worries about the safety of ordinary visible light.

Such satellites would be cheap to produce in quantity and to loft, and their illumination could be sold to any existing solar farm, reducing need for energy storage.

(I acknowledge Alexis Gilliland for inspiration.)