For decades, the Pentagon has been the world'slargest oil consumer, and as global petroleum prices continue to rise, the military has been searching for feasible energy alternatives. Now they're looking in space.

The U.S. Naval Research Laboratory (NRL) is building technology that will allow the military to capture solar power in orbit and project it back down to Earth. Not only would space solar potentially save the Pentagon buckets of cash, but it could simplify military deployments. Fuel tankers would no longer have to reach remote or volatile areas, and missions could run longer without having to return to base to refuel.

So far, NRL has built and tested two different prototypes of what they call a "sandwich" module, named for a design innovation that packs all the electrical components between two square panels. The top side is a photovoltaic panel that absorbs the Sun's rays. An electronics system in the middle converts the energy to a radio frequency, and the bottom is an antenna that transfers the power toward a target on the ground.

Ultimately, the idea is to assemble many of these modules in space by robots — something the NRL's Space Robotics Groups is already working on — to form a one kilometer, very powerful satellite.

A second design, a "step" module, modifies the sandwich design by opening it up, which allows it to receive more sunlight without overheating, thereby making it more efficient.

"Launching mass into space is very expensive," said Paul Jaffe, a spacecraft engineer leading the Navy's project, in astatement.

Left: Sandwich module. Right: Step module.

Image: U.S. Navy

It's expected that space solar will be able to produce more energy than ground-based collectors because it can soak up rays around the clock, and regardless of the weather below. Private industry is interested in similar technology. California utility company Pacific Gas & Electric has acontract to buy space solar power from Solaren by 2016. And the Shimizu Corporation of Japan has recently proposed tobuild a 11,000-mile solar strip across the Lunar equator to capture and transfer the sun's energy.

Not everyone is so confident that such an ambitious project can be completed, but, as Jaffe put it, "Hard to tell if it's nuts until you've actually tried."

"People might not associate radio waves with carrying energy, because they think of them for communications, like radio, TV, or cell phones," said Jaffe. "They don't think about them as carrying usable amounts of power."