Power from the final frontier

Giant collectors in space that beam solar energy back to Earth could soon be a reality. And, as James Bloom reports, it could be a bigger moneyspinner than space tourism
Photo: Malcolm Fife/Corbis

At some point 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, which says confidently that we will see "a basic proof-of-concept within 4-6 years and a substantial power demonstration as early as 2017-2020".

It's obvious in some ways: above the atmosphere, a solar cell receives about 40 times more energy per year than an equivalent site on the ground, due to 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 and, eventually, a few square kilometres. Then that energy can be sent to the ground - using, the Pentagon suggests, 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 truly hard and expensive part is going to be getting it into orbit. We'll need regular launches and on-orbit robotic assembly systems. It's a $10bn [£4.8bn] programme, but by 2050 it could deliver 10% of America's power needs."

The space office sees energy supply as one of strategic importance as oil supplies dwindle; according to a report by Germany's Energy Watch Group published last week, "peak oil" output occurred last year, and will fall by 7% annually to half its present levels by 2030. The space office 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 receives about 212 TW-years of energy each year.

Deadly weapon?

The first units to go up will generate between 10MW and 25MW of continuous power, enough for a town of 25,000 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.

"If a 2.45Ghz beam drifted off its target and ended up over a town, the effect would be negligible," says Lt Col Damphousse of the space office. "By the time the microwave reaches the surface it has spread out considerably. The power density is one-sixth that of the noonday sun."

The US army could also use such a device to deliver electricity to its troops. Military units in forward areas pay $1 per kilowatt hour, six times the UK domestic price. They pay a lot more to bring in fuel. Lives could be saved by cutting long and vulnerable logistics chains - though it would require the large collectors.

The beam is most powerful near its source, and although at 25,000 miles 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. "Space Traffic Control would make sure the satellite is not tampered with before launch," says Damphousse. "They would also ensure the spacecraft do not interfere with each other."

Leopold Summerer, head of the Advanced Concepts Team at the European Space Agency, thinks laser beams will be better than microwaves due to 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 been shrunk and Japanese agency JAXA has suffered technical setbacks. The International Space Station barely manages to justify its running costs. As of today, none of the agencies is 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. In a survey of the US space community's National Space Goals conducted last year, launching solar power satellites came top of the list.

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 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.

Test prototype

Space Island Group is a Californian startup with an ambitious strategy. Gene Meyers, its chief executive, says the company has almost completed financing for a test prototype launch at a total cost of $200m. "We expect to have the prototype in orbit within two years," he says. "It will be a 10-25MW system in low Earth orbit, using a microwave beam to deliver the energy to ground stations, probably located in Europe."

Their main competitors are Mitsubishi and an as-yet unnamed European consortium. "Mitsubishi is more advanced in their satellite design, but are stymied by launch costs," Meyers says. Space Island will use Nasa fuel tanks and launch facilities built in the 1970s. "They are designed to handle a launch every week, so the capacity is there to scale up to a larger system," he says. The plan is to have a 100 gigawatt service in operation by 2025.

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.

Leopold Summerer at the European Space Agency 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."

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