A new Pentagon study lays out the roadmap for a multibillion-dollar push to the final frontier of energy: a satellite system that collects gigawatts’ worth of solar power and beams it down to Earth.

The military itself could become the “anchor tenant” for such a power source, due to the current high cost of fueling combat operations abroad, the study says.

Beaming power from space How would a space-based solar power system work? Proponents of the idea argue that the system would have all the benefits of terrestrial solar power - and that energy could be safely beamed back to Earth transmission stations 24 hours a day, seven days a week, during rain or shine. Environmental and technical challenges still have to be met, however, including the challenge of building a network of energy-converting satellites in space. Click through this interactive to see how a space-based power transmission system might work.	Focusing sunlight The biggest elements of a solar-power satellite would be giant mirror arrays, perhaps measuring several miles wide, which would focus sunlight onto photoelectric cells. The geosynchronous orbit would be designed to catch solar rays even when the satellite is pointing at the night side of Earth.
Converting energy The photoelectric cells generate gigawatts of electricity. That electrical power is converted into a microwave beam that is directed downward toward Earth, at a frequency best-suited for transmission through the atmosphere.	Beaming it down The microwave beam is targeted at a rectifying antenna array on Earth. Designers say the beam would have about one-sixth the intensity of noon sunlight.
Back into electricity The Earth receiving station converts the microwave energy back into electricity.	Into the grid Electrical power flows into the power grid, just as if it were generated by a terrestrial source. The typical system design calls for producing 1.2 to 4.8 gigawatts of electricity for local grids.

The 75-page report, released Wednesday, says new economic incentives would have to be put in place to “close the business case” for space-based solar power systems — but it suggests that the technology could be tested in orbit by as early as 2012.

"I think we have found the killer application that we have been looking for to tie everything together that we're doing in space," Air Force Col. Michael V. "Coyote" Smith, who initiated the study for the Defense Department's National Security Space Office, told msnbc.com on Thursday.

Space advocacy groups immediately seized on the idea and formed a new alliance to push the plan. But a representative of the solar-power industry was doubtful that space solar power would move from the realm of science fiction into reality anytime soon.

"You've got a lot of technology breakthroughs that you have to make," Mike Taylor, technical services manager for the Solar Electric Power Association, told msnbc.com.

Charles Miller, president of Space Policy Consulting as well as president and chief executive officer of Constellation Services International, said the key to the plan's success has more to do with economics than physics.

"The issue here is not technology, OK?" said Miller, who was a contributor to the study. "You could figure out how to do space solar power in the '70s. [But] you couldn't close the business case in the '70s. You couldn't close it in the '90s. How do you close the business case? That is the No. 1 question to be answered."

Economic equation is changing
The report — which was done on an unfunded basis and took advantage of online collaboration with outside contributors — notes that several factors have changed in the decade since NASA took its most recent in-depth look at the space power concept (PDF file). Today's best solar cells are about three times as efficient as they were in 1997, while crude-oil prices are roughly three times as high. And in the post-9/11 era, energy security has taken on far more importance.

"The technology has advanced vastly, and the security situation has changed quite a bit, as well as the economic situation," Marine Lt. Col. Paul Damphousse, who took over the study from Smith last month, told msnbc.com. "Those things warranted another look."

Those factors still don't make space solar power attractive for commercial users, but a better case could be made for the Defense Department. The U.S. military pays a premium for its power in the battlefield, when you consider the cost of shipping oil out of the Middle East, refining it, then shipping the fuel back to the combat zone and burning it in electrical generators, Miller said. All that brings the current power price tag to $1 or more per killowatt-hour, compared with 5 to 10 cents on the domestic market, the report says.

Even then, the economic equation still doesn't add up, due primarily to the high cost of launching payloads to orbit. But in the near future, the U.S. military could become a potential "anchor tenant customer" for space-generated power, the report says.

"The business case may close in the near future with appropriate technology investment and risk-reduction efforts by the U.S. government, and with appropriate financial incentives to industry," the report says.

Smith said the military would prefer to buy its power from a commercial space provider, rather than operating the system itself. "It is our goal to move this entire project out of DOD [the Department of Defense] as quickly as possible," he said. "Energy is not our business. We want to be a customer."

How it could work
The report sketches out how a space-based solar power system could work:

• A network of satellites would be constructed in space with arrays of lightweight mirrors extending for several miles (kilometers) on each side.
• Those mirrors would focus sunlight on solar cells, generating electrical power. The electricity would be converted into microwaves suitable for transmitting through Earth's atmosphere, at frequencies of 2.45 or 5.8 GHz.
• The microwaves would be directed down to antenna arrays on Earth, as a beam of radiation about one-sixth as intense as noon sunlight. The antennas would convert the radiation back into electricity for distribution via conventional grids.

The commercial systems discussed in the past would deliver 5 to 10 gigawatts of power. In contrast, the Pentagon study calls for military systems providing 5 to 50 megawatts of continuous power — roughly a thousandth as much.

The report's roadmap calls for ground-based technology development over the next few years, leading up to a demonstration in low Earth orbit in the 2012-2013 time frame, and in geosynchronous orbit by 2017. However, the report makes no commitment for funding such a demonstration. Smith said that would be up to other agencies — such as the Pentagon's own Defense Advanced Research Projects Agency, or NASA, or the proposed Advanced Research Projects Energy.

Damphousse said the program could use an "incremental approach," starting with experiments to transmit power wirelessly between ground stations placed miles apart. "If you can do that, then you're well on your way to proving you can do it from space," he said.

A follow-up experiment could try transmitting power from the international space station to Earth. "I actually met with a bunch of folks at NASA Ames last week ... and they warmed to the idea immediately," Damphousse said.

Damphousse said the geosynchronous system would require an investment on the order of $10 billion, but would serve as a proof of concept for commercial space power systems.

Smith said such systems could eventually deliver electricity to places that lack the infrastructure for traditional power transmission grids, and turn the decades-old dream of wireless power into reality. "It's using space for an actual tradeable commodity — not for a rover on Mars, which is also necessary — but actually delivering a commodity that can be given to anybody in the world," he said.

Time for a reality check
In conjunction with the Pentagon report's release, 13 space advocacy and research organizations announced the formation of the Space Solar Alliance for Future Energy, which pledged to push for implementation of the space power plan.

"While the technical challenges are real, significant investment now can build space solar Power into the ultimate energy source: clean, green, renewable, and capable of providing the vast amounts of power that the world will need. Congress, federal agencies and the business community should begin that investment immediately,” Mark Hopkins, senior vice president of the National Space Society, said in a written statement.

It's up to policymakers, business leaders and voters to decide whether space-based solar power, or SBSP, is worth pursuing, according to the acting director of the Pentagon's National Security Space Office, Joseph Rouge.

"It appears that technological challenges are closing rapidly and the business case for creating SBSP is improving with each passing year," Rouge said in his foreword to the report. "Still absent, however, is an appropriate catalyst to stimulate the various interested parties toward actually developing a SBSP capability."

The Solar Electric Power Association's Taylor, who advises utilities and other organizations on trends in terrestrial solar power, said the space option "is not something that's on the current solar industry's radar."

He told msnbc.com that putting a large power-generating system in space would pose huge technical challenges — and the potential payoff would have to be similarly huge to justify the risk and expense.

"I'm not sure there'd be a great need to move into space unless it had some exponential cost improvement," Taylor said. "It can't be just a marginal improvement."

What is to be done?
Smith agreed that the hurdles were high. "You put the study out, you spend a couple of weeks getting comments, you step back and take a breath, then you get busy," he said. "We didn't try to candy-coat this. This is going to be a hard, hard, hard, hard problem."

No. 1 on his list was reducing the cost of sending payloads into geosynchronous orbit — a cost that is currently estimated at $10,000 per pound or more. "We have got to solve the reusable rocket and space plane problems immediately," Smith said. "It's time to stop just talking about it."

Constellation Services International's Miller said "the business case doesn't close by just standing aside and doing laissez-faire." He called attention to three recommendations listed in the Pentagon report:

• The Defense Department should analyze its long-term requirements for energy delivery to warfighters, and evaluate whether there's an appropriate way to sign up as an anchor customer. The report cited the example of the National Geospatial-Intelligence Agency's status as an anchor customer for the commercial NextView satellite program.
• Government incentives for carbon-neutral energy technologies — such as carbon/pollution credits and offsets as well as loan guarantees — should be extended to space power programs as well. The loan guarantees could be modeled on the program currently provided to the nuclear power industry.
• Legislation should be enacted to create transferable investment tax credits for private investments in reusable space transportation systems, as well as in commercial space infrastructure such as orbital fuel depots and assembly platforms.

Miller noted that the energy market amounts to $1 trillion a year market, and said the future payoff could be at least as huge as the present challenges.

"If space solar power takes off, everything that came before — Apollo, the shuttle, the station, all together — will look like a college science project," Miller told msnbc.com. "It's that much bigger."