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04 Jan 2008 06:00
Some time before 2050, satellites collecting solar power and beaming it back to Earth will become a primary energy source, streaming terawatts of electricity continuously from space.
That’s if you believe a recent report from the Pentagon’s National Security Space Office (NSSO).
It is obvious in some ways: above the atmosphere, a solar cell receives about 40 times more energy a year than an equivalent site on the ground, because of the absence of atmospheric scattering and seasonal or nightly reductions in light.
The NSSO suggests that an orbiting spacecraft with solar panel arrays would be comparable to current ground-based installations spanning hectares.
That energy can be sent to the ground using a giant laser or microwave beam.
The report, Space Based Solar Power as an Opportunity for Strategic Security, suggests optimistically that one application will be the beaming of “energy aid” via satellite into conflict and disaster zones, minimising the human cost of resource wars and catastrophic events caused by global warming.
“The technology has been in development for a while,” says Joseph Rouge, associate director of the space office.
The space office sees energy supply as being of strategic importance as oil supplies dwindle and notes that all remaining oil resources are estimated to contain 250 terawatt-years of energy, but that a one-kilometre wide band in geosynchronous orbit would receive about 212 terawatt-years of energy each year.
The first units to go up will generate enough for a town of 25Â 000 people. If the energy is transmitted by microwave, a surface array one-tenth of a square kilometre in size will be needed to pick it up. Larger beams will require larger collector arrays.
But wouldn’t a microwave beam from space be equivalent to a deadly weapon? Unlike photovoltaic cells, these antenna arrays are practically transparent, so crops could be planted under them.
The US army could also use such a device to deliver electricity to its troops. Military units in forward areas pay $1/kWh, six times the United Kingdom domestic price. They pay a lot more to bring in fuel. Lives could be saved by cutting long and vulnerable logistics chains.
The beam is most powerful near its source and, although at 40Â 000km up it would not pose a risk to astronauts in the International Space Station, it could be turned against communication or observation satellites in geostationary orbit.
Leopold Summerer, head of the advanced concepts team at the European Space Agency, thinks laser beams will be better than microwaves because of their higher transmission frequencies and narrower apertures. His department has been coordinating exploratory discussions between the big European energy suppliers and aerospace companies.
“By the time space solar power is ready, there will already be large-scale terrestrial solar in place,” Summerer says. “The same panels could be used to receive energy from a laser. You could save a lot of money on energy storage by beaming at night and throughout the year.”
The various platforms under consideration will not be competitive until the cost of space flight goes down. Nasa’s budget has shrunk and Japanese agency Jaxa has suffered technical setbacks. The International Space Station barely manages to justify its running costs.
None of the agencies is currently funding a space solar power launch. Rouge says: “This is a commercial venture. The US government could be an initial customer, but they won’t be the ones to build it.”
Solar power beaming could be much more profitable than space tourism. It has the potential to drive down launch costs, thereby making a number of other missions practicable.
Over the past 40 years, microwave and laser power transmission systems have been tested successfully in Europe, the US and Japan. Unmanned aircraft and lunar rovers receiving power from a remote beam are proven applications.
The Japanese have also tested reactions in the ionosphere to microwaves at the frequencies used for space solar power, and the results were positive. The only remaining issue is to test a large-scale system.
Space Island Group is a Californian start-up with an ambitious strategy. Gene Meyers, its chief execuÂtive, says the company has almost completed financing for a test prototype launch costing $200million.
Their main competitors are Mitsubishi and an as-yet unnamed European consortium.
Space Island will use Nasa fuel tanks and launch facilities built in the 1970s.
The Indian government has expressed interest in becoming a customer. Many rural areas are undergoing development but do not have access to the national grid. There are also a large number of island nations paying excessive amounts to distribute electricity.
Summerer says: “I think we’ll use the technology sooner or later. If one nation develops this service, the others will take it seriously. They won’t be able to resist.”—Â
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