Published online 16 September 2008 | Nature | doi:10.1038/news.2008.1109


Beaming energy from space

A small step towards a very grand vision

Solar power satelliteDemonstrating this technology might cost as little as ten billion dollars.Mafic Studios, Inc

The idea that Earth's energy needs might be met by giant arrays of orbiting solar panels has been around since the 1960s1. As president of the Space Power Association, an international organization focused on this visionary scheme, John Mankins has long experience of the scepticism it engenders. His latest technical demonstration, the results of which were announced last week, was designed to make the idea look a little more practical.

By transmitting microwaves from Maui to the neighbouring island of Hawaii, Mankins has shown that energy could be transmitted all the way through the atmosphere. The small-scale demo, which took only four months to prepare and cost less than US$1 million, was featured on the Discovery Channel's Project Earth programme last Friday. Mankins says that the work, which brought together specialists from the United States and Japan, shows that "it is possible to make real progress quickly, affordably and internationally."

Eternal sunshine of the spotless satellite

Even on a sunny afternoon, Earth's atmosphere absorbs or scatters half of the Sun's rays. Panels in space could collect the full whack: 250 watts per square metre. And that power would be available 24/7, without interruption by clouds or night. That energy could then be beamed to the surface in the form of microwaves which, unlike sunlight, should pass unhindered through the 100-km thick layer of atmosphere around the planet.

“Graphic artists can put anything in space. John Mankins has done something real.”

Roger Harrison
Eisenhower Center for Space and Defense Studies

Mankins and his team set out to show that this last part of the idea could hold up. An array of eight transmitters on top of the volcano Haleakala on Maui sent a 20-watt pulse that was picked up by signal detectors at Mauna Loa Observatory on Hawaii's Big Island, more than 100 km away. The beam was not well collimated, though, and the energy at the receiving end was mere fractions of a microwatt.

Mankins hopes that this demonstration will get funding agencies to pay attention to space-based solar power. He estimates that with less than $10 billion he could put a 5–10 megawatt pilot plant in orbit by 2018, using conventional satellite launchers.

"We can become, in the future, a bigger energy player than Saudi Arabia is today," says Mark Hopkins, senior vice-president of the National Space Society, a non-profit organization that supports space-based solar power. And, Hopkins says, a constellation of satellites could beam energy all over the globe, transforming the standard of living for people in impoverished nations.

Thousands of spacecraft, trillions of dollars

Enthusiasts and some others say that the technology for solar collectors and wireless energy transmission is starting to catch up with what was once an impossible dream. "I think it's an idea whose time may have come," says Roger Harrison, director of the Eisenhower Center for Space and Defense Studies in Colorado Springs. "I would be a little sceptical, but I'm more than happy to be proven wrong."

The problem is that the cost remains out of this world. Mankins envisages arrays of thousands of satellites beaming energy to hundreds of receivers spread across all continents. He hopes to cut costs by mass-producing the lightest modules possible, but each of those satellites is still mass that would have to be launched into space. Roger Angel, an astronomer at the University of Arizona in Tucson, has calculated the cost of similar ambitious projects and says that such a weighty system can't hope to compete with cheaper alternatives on Earth. Currently, it costs US$20,000 for every kilogram sent into space, Angel says. That cost would have to come way down. "It puts this stuff pretty far in the future," he says.

The Hawaii demonstration is a small step, merely suggestive of the potential of space-based solar power. But stepping away from the drawing board is, in itself, an accomplishment. "This field of study is infected with graphic artists," Harrison says. "But graphic artists can put anything in space. John Mankins has done something real, and I think that's to be admired." 

  • References

    1. Glaser, P. E. Science 162, 857-861 (1968). | Article | PubMed | ISI |
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