(Agencies)
Updated: 2007-12-24 11:09

The energy captured by space-based photovoltaic arrays would be converted into microwaves for transmission to Earth, where it would be transformed into direct-current electricity.

Low-orbiting satellites, as proposed for Palau, would pass over once every 90 minutes or so, transmitting power to a rectenna for perhaps five minutes, requiring long-term battery storage or immediate use -- for example, in recharging electric automobiles via built-in rectennas.

Most studies have focused instead on geostationary satellites, those whose orbit 22,300 miles above the Earth keeps them over a single location, to which they would transmit a continuous flow of power.

The scale of that vision is enormous: One NASA study visualized solar-panel arrays 3 by 6 miles in size, transmitting power to similarly sized rectennas on Earth.

Each such mega-orbiter might produce 5 gigawatts of power, more than twice the output of a Hoover Dam.

But how safe would those beams be?

Patrick Collins of Japan's Azabu University, who participated in Japanese government studies of space power, said a lower-power beam, because of its breadth, might be no more powerful than the energy emanating from a microwave oven's door. The beams from giant satellites would likely require precautionary no-go zones for aircraft and people on the ground, he said.

Rising oil costs and fears of global warming will lead more people to look seriously at space power, boosters believe.

"The climate change implications are pretty clear. You can get basically unlimited carbon-free power from this," said Mark Hopkins, senior vice president of the National Space Society in Washington.

"You just have to find a way to make it cost-effective."

Advocates say the US and other governments must invest in developing lower-cost space-launch vehicles. "It is imperative that this work for `drilling up' vs. drilling down for energy security begins immediately," concludes October's Pentagon report.

Some seem to hear the call. The European Space Agency has scheduled a conference on space-based solar power for next Feb. 29. Space Island Group, another entrepreneurial US endeavor, reports "very positive" discussions with a European utility and the Indian government about buying future power from satellite systems.

To Robert N. Schock, an expert on future energy with the UN's Intergovernmental Panel on Climate Change, space power doesn't look like science fiction.

The panel's 2007 reports didn't address space power's potential, Schock explained, because his team's time horizon didn't extend beyond 2030. But, he said, "I wouldn't be surprised at the beginning of the next century to see significant power utilized on Earth from space -- and maybe sooner."

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