Where the Sun Does Shine
Will space solar power ever be practical?
- By Linda Shiner
- Air & Space magazine, July 2008
(Page 2 of 3)
Wireless power transmission, the means by which the collected solar energy is delivered to the ground, has also progressed. Even 30 years ago, the basic technique was known to work. In fact, the distance record for microwave beaming was set in 1975 at the Jet Propulsion Laboratory’s Goldstone facility near Barstow, California. Experimenters transmitted 34 kilowatts of power to a receiver almost a mile away, and more than 82 percent of it was converted to electricity. In 1993, researchers from Kobe University in Japan and Texas A&M University used a transmitter and receiver launched on a sounding rocket to demonstrate microwave transmission in space for the first time.
Techniques for building sunsats have not come as far. The 1979 study envisioned hundreds of astronaut spacewalkers toiling for decades. Robotic assembly would be more practical. But despite the sometimes photogenic robots creeping around NASA centers and university laboratories, the only construction project in space, the International Space Station, is still being assembled by astronauts.
Not that the field of space robotics isn’t advancing. Robots that may someday build large structures in orbit might look like Roby Space Junior, a spiderbot created by an institute at the Vienna University of Technology (famous in Europe for creating a tiny robot soccer team). The four-inch-square Roby was designed to crawl on a vast web-like structure called a Furoshiki spacecraft, a lightweight mesh that could form the platform for large antennas, sails—or solar collectors. In 2006, the European and Japanese space agencies joined forces to launch a 65- by 130-foot Furoshiki web and three spiderbots on a sounding rocket that produced a few minutes of weightlessness. The net deployed, and the robots crawled on it for a few seconds.
The experiment seems typical of recent work on space solar power: ingenious, but a long way from tackling the huge challenges that space power systems face. The Japanese and European space agencies are funding research, but as of today, there is no credible project to build systems that will demonstrate all the necessary elements working together.
If he had the $850 million annual budget he once managed at NASA, Mankins would spend a big chunk of it to develop modular systems, a building-block approach to the assembly of large space structures. He likens it to lots of small, networked computers replacing a few big, powerful supercomputers. “If you think of trying to build a single mainframe with 1960s technology that had the processing capabilities of the Internet, it would be the size of Manhattan. But think of the Internet: You have these millions of individual computers working cooperatively over a network.”
The “modular” in modular systems represents tens of thousands of identical, mass-produced (and therefore cheap) parts. Each part, because of advances in solid-state electronics, could serve as both collector and transmitter. “Think of an Iridium satellite,” says Mankins. The Iridium network uses 66 satellites to provide wireless communication worldwide. “It has integrated into [a satellite] the size of a VW Bug power generation, intelligence, attitude control, and microwave phased arrays.” Now imagine that satellite flattened into a tiny hexagon, one of 10,000 collecting-transmitting hexagons on a single satellite.
That’s the kind of innovation Mankins wants to see funded. But to which federal agency should he apply? Neither NASA nor the Department of Energy has ever shown much interest in nurturing sunsat technology.
If the government put money into space solar power, would taxpayers get a return on their investment? Molly Macauley, an economist with Resources for the Future, a Washington, D.C. energy and environment think tank, has studied the ability of sunsats to compete with other renewable energy technologies. It’s a hard case to make, she says. “Advocates of space solar power fail to acknowledge that technological change and innovation are happening in other types of renewable energy—ground-based solar power, concentrated solar power, wind, geothermal energy. The ability to compete on a cents-per-kilowatt-hour basis is going to get more difficult, not less difficult.”