FYI,

"How Satellites Could Power the Future"
Live Science
http://www.livescience.com/environment/080618-pf-space-solar.html

: Placing solar panels in space above both night and clouds was first
: considered 40 years ago. But the estimated cost was, in a word,
: astronomical.

: The idea, however, has seen a resurgence, thanks to rising oil
: prices and advances in solar technology. A report from U.S. Defense
: Department found that space-based solar is technically feasible and
: economically viable.

: To help prove the point, the Air Force Academy recently announced
: plans for a small demonstration satellite that would beam down a
: meager, but still significant, 0.1 watts of solar power.

: "Our vision is to build the world's first-ever space-based solar
: power system to light a single bulb on Earth and in so doing light
: the path for business to follow," said Col. Michael "Coyote" Smith
: of the Air Force.

: The type of transmission beam is still not decided, but the project
: may benefit from separate research in Japan that has been studying
: the two most likely technologies: microwaves and lasers.

: In the full light of space

: The sun puts out more than 10 trillion times the energy currently
: being consumed by the whole world.

: "We would only need to tap into a small fraction of that to get all
: our energy now and in many years to come," said Mark Hopkins,
: senior vice president of the National Space Society, which recently
: formed an alliance with other non-profits to promote space-based
: solar.

: The advantage of going to space is that sunlight is constant up
: there and three to 13 times stronger than the average down here on
: Earth, Smith said.

: The first suggestion of a solar power satellite was in 1968, but
: early estimates put the price tag around $1 trillion, largely
: because astronauts would have had to construct the facility back
: then.

: Now robots can do the job, installing improved-efficiency solar
: cells in a modular fashion, for 100 times cheaper than before.

: "If you decide to go now with today's technology, you're talking
: about the same cost as ground-based solar," Hopkins said, which is
: around 30 cents per kilowatt-hour.

: That's still too high, according to Hopkins, but he thinks costs
: will continue to come down, especially if development dollars start
: coming in. The Pentagon-sponsored report offered a roadmap for how
: to build a 10-megawatt test satellite over the next 10 years for
: $10 billion.

: But where that money will come from is hard to say. According to
: Hopkins, NASA sees this as an energy application and the Department
: of Energy sees this as a space enterprise.

: "There are bureaucratic problems finding a home for this project,"
: he said.

: Japan plans ahead

: The Japanese space agency, JAXA, has been providing steady support
: over the past decade for their Space Solar Power System (SSPS). The
: goal is to launch a geostationary satellite by 2030 that could
: supply 500,000 homes on Earth with a gigawatt of power.

: Currently, JAXA researchers are looking at both microwaves and
: lasers as possible options for beaming the energy down.

: "The technology for microwave transmission is more advanced, since
: it is based on current communication satellites," said Susumu
: Sasaki, a manager at JAXA's Advanced Mission Research Group.

: But to transmit huge amounts of power in a focused beam, the
: transmitting antenna in space needs to be roughly 2 kilometers
: (1.2 miles) wide. A receiving antenna of similar size or bigger
: must be built on Earth.

: The alternative would be a laser. Japanese scientists have been
: working on metal alloy plates that can absorb sunlight and directly
: convert it into an infrared laser beam.

: The advantage is that the transmitting and receiving devices can be
: about 10 times smaller than for microwaves, Sasaki said. Lasers
: also do not carry the risk of interfering with communication
: networks that use microwaves.

: However, lasers cannot go through clouds like microwaves can, so
: about half of the beam energy is lost if lasers are used.

: Another problem is that a laser-beaming satellite sounds like a
: weapon, even though Hopkins thinks there would be ways to ensure
: that it never gets used in such a way.

: In contrast, microwave transmission is too low of intensity to be
: considered dangerous. A person could safely walk across where the
: targeted beam hits the Earth, according to Hopkins.

: "You would feel it as some extra warmth, like on a sunny day," he
: said.

: Sooner than later

: Smith said that both microwaves or lasers were being considered for
: the Air Force project, which was announced earlier this month at
: the International Space Development Conference.

: "Although our architecture is far from decided, we have adopted the
: mantra keep it cheap and simple and deliver it soon," he said.

: They plan to stay under $10 million with a 400-pound (181-kilogram)
: satellite in low Earth orbit. It may be able to piggyback on
: another mission and use inflatable solar arrays. Smith hopes it
: will launch in 2010.

: "We want to get this rolling," he said.

Mark Reiff