Solar power satellite

Solar space power: may the power be with you

The concept of beaming power to Earth from orbiting satellites dates back to the 1960s so why is there still an energy crisis? E&T investigates.

The late 1960s was a time of infectious optimism in the burgeoning space community and, with men about to set foot on the Moon, almost anything seemed possible. So, in 1968, when aerospace engineer Peter Glaser proposed collecting power from a 'mile-wide' solar array in geostationary orbit and beaming it down to Earth using microwaves, it all seemed perfectly feasible.

But it was an idea ahead of its time: not only were there numerous technical issues to surmount, the driving incentive from the energy market was absent. Oil was cheap and no one had heard of global warming, so why did they need solar power satellites?

Earlier this year, however, the case for Space Solar Power (SSP) seemed to snap into focus when leading space systems manufacturer EADS Astrium revealed a proposal to conduct a demonstration mission. Announcing its belief that space technology was now sufficiently mature to build a satellite capable of delivering 10-20kW of usable power within a five-year timeframe, the company cast its net for partners to invest in its vision.

With Japan planning a similar demonstration for 2020, and President Obama's recent retargeting of Nasa funds towards technology programmes, it seems the time for power from space may be nigh.

Technology Constraints

Almost as soon as the ink was dry on Glaser's patent for a space-based solar power system, the potential 'technology showstoppers' began to take centre stage. They included, among others, the large area of expensive and not-very-efficient solar cells required, the high cost of launching the hardware to geostationary orbit, the unproven technology of wireless power transmission and the safety issues (real or assumed) surrounding the collection of power on the ground.

Ralph Nansen, former solar-power satellite programme manager for Boeing and author of the 2009 book 'Energy Crisis: Solution from Space', has been involved with the concept since the late 1970s when Boeing E F began its study of a solar-power satellite. While recognising that technology has advanced significantly since then, Nansen told E&T that 'the technology available at the time was advanced enough to proceed with development' despite what naysayers believed.

For example, proclaims Nansen, 'the solar cells we selected for the Boeing satellite were single crystal silicon (only 2mm thick), 16.5 per cent efficient, and had a very long potential life in orbit because they were so thin'. Of course, this also made them light. Nansen also asserts that the projected costs for mass-produced cells were 'low enough to make the satellite energy cost-competitive with other sources'.

As for launch costs, he cites a proposal to use a 'two-stage, fully-reusable flyback system' based on Apollo-Saturn rocket stages that could have brought costs down, were it not for a 'misguided' decision to develop the Space Shuttle instead. The Shuttle was 'an unfortunate configuration that has actually inhibited the development of fully reusable launch systems, while creating an image that low-cost space transportation is impossible', says Nansen. Whatever the reason, industry's wish for low-cost access to space remains unfulfilled.

Finally, regarding power transmission, Nansen refers to Glaser's original proposal: 'The transmitter was based on the work of Bill Brown of Raytheon, who demonstrated the first successful wireless power transmission in 1964 when he powered a model helicopter', he says. Moreover, states Nansen, 'there is no real safety problem. The most comprehensive testing has been done by the US military - because they operate high-power radars - and they found no permanent damage to cells as long as the energy level was less than about 1,000W/m2'. Nansen adds that tests on insects, birds and other lifeforms produced no damage with power densities below this heating threshold, and that standards for SSP systems would be the same as for microwave oven leakage. 'It is very clear that any safety issues are assumed and not real,' he insists.

Demonstrator

So why, if SSP is so feasible, and given the current energy crisis, has none of the world's space agencies chosen to fund a technology demonstration mission? John Mankins, former Nasa engineer and now President of the Space Power Association told E&T that SSP represents 'a classic conundrum' in that 'energy agencies don't do space, and space agencies don't do energy'.

Of course, the idea of a demonstrator is to prove the technology works, which is where EADS Astrium's proposal for a demonstration satellite comes in. Based on the AlphaSat platform currently under development by a European consortium, it would provide up to 20kW of DC power from its solar arrays.

According to Astrium's chief technical officer Robert Laine, recent advances in solar cell efficiency and laser technology in Europe have brought the idea much closer to reality. Indeed, Astrium has been working with its subsidiary, Surrey Satellite Technology, 'on converters that would transform the laser signal into energy', meaning that most of the required technology is available 'in-house'.

EADS has made it clear that the demonstration will not go ahead without partners - space agencies, national governments or even power companies - to help fund the project. Nevertheless, foreseeing the need for 'a group of partners from across both the energy and space sectors', Matthew Perren, Astrium's innovation manager, confirmed that 'Astrium has received many expressions of interest from a number of potential partners, both institutional and commercial'.

A proposal for a solar power satellite announced by the Japan Aerospace Exploration Agency (JAXA) in 2008 has a similar goal, with a more powerful 10MW demonstrator planned for 2020, but the agency also hopes to be able to deliver a gigawatt from space by 2030. Although researchers have made progress in demonstrating an 800W optical-fibre laser and mirrors that reflect light efficiently at 1m - a frequency chosen for its ability to pass through the atmosphere with limited attenuation - some other reported numbers make the project look like science fiction. Kilometre-long solar panels, spacecraft masses in the thousands of tonnes, and price tags in the 'tens of billions' make an operational system seem further away than the elusive fusion reactor.

With launches of five-tonne satellites currently costing upwards of $50m, 'the cost of launch is certainly a hurdle', confirms Mankins. 'However, launch costs are driven by markets more than anything else,' he says, and launches are so expensive because there are so few of them per year. In fact, in Mankins's opinion, the emergence of a large new commercial market for launches, such as SSP, 'will bring down the cost dramatically of getting to space'.

Contract

Launch costs haven't discouraged a Californian start-up company, Solaren, from developing a system capable of delivering some 200MW from geostationary orbit by 2016. Solaren's Director of Energy Services Cal Boerman declared that they could install their system with as few as 'only four' launches by using a design that is 'lightweight and innovative'.

Technical details are somewhat thin on the ground, but the interesting aspect of this company's development is a contract it signed with California's biggest energy utility, Pacific Gas and Electric Company, in April 2009. The contract letter (with California Governor Arnold Schwarzenegger's name at its head) and supporting documents are in the public domain and make interesting reading.

'If completed by 2016', it states, 'the project would deliver an average of 850GWh for the first year of the term, and 1,700GWh per year for the remaining term' of the 15-year power purchase agreement. Purchase prices are said to be comparable with other renewable energy sources.

Solaren's CEO, Gary Spirnak, says: 'While a system of this scale and exact configuration has not been built, the underlying technology is very mature and is based on communications satellite technology.'

Ralph Nansen agrees: 'I've had an operational demonstrator functioning 24 hours a day, with no failures or interruptions, for years in my side yard: it is called satellite TV. It receives radio frequency energy from a transmitter in geosynchronous orbit using energy generated by solar cells on the satellite. It maintains its orbit position and attitude. It has all the functions of a solar power satellite except for the energy level.'

In support of SSP's feasibility, Solaren's contract documentation cites a demonstration of wireless power transmission conducted by Nasa's Jet Propulsion Lab in 2008 which transmitted RF energy over a distance of 148km between two Hawaiian islands, achieving 'greater than 90 per cent conversion efficiency of RF energy to electricity'.

It all seems too good to be true, and those weaned on terrestrial power systems remain to be convinced 'but that is what the demonstrators are for. After all, when Arthur C Clarke published his proposal for geostationary broadcast platforms in the October 1945 issue of Wireless World magazine (a prescient magazine title if ever there was one), few believed that communications satellites were possible.

Tipping Point?

Recognising that renewable power sources are the way forward, at least to some degree, world governments are gradually introducing programmes to close the energy gap. But progress with wind and wave power has been relatively slow and the pendulum has already swung back towards nuclear power, despite its detractors.

Time was that nuclear fusion was seen as the solution, but as retired Boeing engineer Gordon Woodcock pointed out at the International Space Development Conference, 'thermonuclear fusion is considered to be 30 years in the future now but it was 30 years in the future 50 years ago!'.

So, do space power proponents think a point will arise when terrestrial power supplies become so inadequate that SSP is a necessity?

According to Nansen, we are seeing the evidence already. 'It is pretty clear, from several regional markets, that the world is at or very near peak oil production', he says. 'This means that the price will continue to climb in spurts and starts, invariably ever higher'. With electricity demand and atmospheric pollution growing in a sort of 'unholy alliance', he expects a 'serious realisation of the problems to sink in within the next 10 to 20 years'.

John Mankins is more forthright: 'If we wait to develop revolutionary new energy sources such as SSP until the existing terrestrial power supply reaches a tipping point, it may already be too late. The time to light the next candle is before the first one goes out - not after you're sitting in the dark!'

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