Solar power from space is an old chestnut, first proposed by NASA’s Dr. Peter Glaser in 1968. He envisioned a constellation of satellites in geostationary orbit, each of them ten kilometres long and five kilometres wide, beaming power down to Earth. NASA and the Department of Energy (DoE) first studied the concept in the mid-70s, but deemed the project technically-but not economically-feasible. NASA took a fresh look in the 90s, and shelved it once more. Its last work related to space power wound down in 2003.
Yet space solar power (SSP) and lunar solar power (LSP), a more radical proposal championed by Dr. David Criswell, of the University of Houston, are two ideas for quenching mankind’s thirst for energy that refuse to go away. An LSP system would litter the surface of the moon with hundreds of power bases, each made up of fields of solar collectors and a microwave emitter that beams power down to massive rectenna arrays on earth. A demonstration system that could beam 1,000 megawatts down to earth would take 10 years and cost $20 billion-assuming a moon base is already built. A full-fledged system would cost half a trillion dollars and take 15 years to build, but would begin to pay for itself. Ultimately, 20,000 gigawatts of emissions-free solar power from the moon could meet mankind’s estimated energy needs in 2070.
Three factors have improved the odds for space-based power, says Dr. Michael Duke, of the Colorado School of Mines. Solar power technologies have improved. Thin film photovoltaics that tap the infrared part of the light spectrum as well as the visible and can be painted onto a glass surface promise great increases in conversion efficiency. Secondly, world energy consumption is set to grow by nearly 60 per cent by 2025. Lastly, NASA has committed itself to returning to the moon by 2018, and plans for a semi-permanent moon base as early as 2022.
The variable that has stayed flat is the cost of getting to space. No matter, argues Dr. Criswell, as most of the LSP system’s infrastructure can be manufactured in situ by giant automated factories from resources readily found on the moon. Lunar regolith, or moon dirt, is a fine powder with jagged grains of iron and glassy silicon. It is easily sintered with microwaves, and all kinds of glassy surfaces and building materials can be fashioned from it.
LSP has a big drawback, though, points out John Mankins of the Sunsat Energy Council, an organization founded by Dr. Glaser that champions SSP. Energy beams in motion tend to spread out, so sending a finely focused beam from the moon to earth requires a transmitter ten times larger than sending a similar beam from geostationary orbit. It might prove more practical to construct pieces of solar power satellites on the moon, and then bolt them together in geostationary orbit. After a period of inactivity, Sunsat Energy Council met in Washington, DC last month, to plan ways to drum up support for space-based power.
Meanwhile, the European and Japanese space agencies are still studying SSP, and writing reports, but they estimate practical results are still decades away. A recent European Space Agency study calculated the economics of SSP in the 2025 to 2030 era. NASA is showing no interest in the idea, though, and the DoE continues to pour resources into fusion research, says Mr. Mankins, himself a former NASA hand. “This subject, which is far more technically feasible than fusion, is kind of between the cracks-no one will touch it,” he says. This chestnut ain’t roasted yet.
