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Giant leap for space-based solar

24 November 2011 Sarah Blackman

Solar power is entering into a space age thanks to the rocketing speed of technology development. Sarah Blackman explores the technical and economical feasibility of launching satellites capable of securing sunlight into orbit.

It's been a mere 30 years since the first commercial solar plants were built on Earth - a short stint compared to the length of time fossil fuels have been meeting our global electricity needs - yet, the speed of technological development has allowed us to think realistically about orbiting these renewable energy structures in space, in the not too distant future.

The concept of collecting sunlight in space and transmitting it back to Earth is not new. In fact, the first Satellite Solar Power System (SPS) was described by American scientist Peter Glaser in 1968. He was granted a US patent for his method of transmitting power over long distances, from the SPS to the Earth's surface.

Since then, numerous studies have been conducted to test the feasibility of such an engineering project, but the expense of putting the required materials in orbit has, so far, stood in the way of a successful launch.

The emergence of policy goals for reducing CO2 emissions and the ever-increasing demand for limitless supplies of energy, however, could outweigh financial risks and open up the potential for investments.

Power perks

"Whoever takes the first mission to launch clean, renewable energy in space, will be the world leader."

There are many reasons why space solar power (SSP) could be a key contender in meeting our global energy needs. For one, orbiting-satellites can be exposed to a constant degree of solar radiation, while Earth-based solar projects can collect 12 hours of solar radiation a day, at most.

SSP has also been proven to collect a higher rate of sunlight as the transmission of solar energy in space is unaffected by atmospheric gas, plant and wildlife interference.

In addition, space solar power can be 'dispatchable' to various locations on Earth as and when the market requires the power. No other power plant has the ability to do this.

The International Academy of Astronautics (IAA) has reiterated the benefits of SSP in the First International Assessment of Space Solar Power, published in November, and identified principal drivers for the deployment of this energy source.

Firstly, global populations are likely to increase and therefore, the worldwide demand for energy is projected to rise significantly. In addition, there is an urgent need to develop large renewable energy resources to reduce emissions of greenhouse gases. Finally, there is the growing uncertainty in global supplies of existing fossil fuels.

John Mankins, a 25-year Nasa veteran and head of the IAA study, believes there is still a place for fossil fuel sources to contribute to global economies, but they are far from limitless.

He said: "There is a consensus among scientists that greenhouse gas emissions pose a great risk of irreversible global climate change. Hence, during the course of the century, it seems critical that the mix of energy sources must shift away from fossil fuels, even as the overall demand for energy soars.

"Space solar power could make a significant contribution to meeting these global energy needs, once needed engineering development and demonstrations are carried out, perhaps providing - for example - 10% to 20% of total demand."

Out of this world technology

Orbiting satellites capable of collecting solar energy and beaming it to Earth appear technically feasible within a decade or two, based on technologies now in the laboratory, according to the IAA's findings.

Key technologies needed to realise solar power generation from space include light-weight, mass produced space systems, from which the solar power satellite would be constructed, and scalable autonomous space robotics to assemble and maintain the platform in space.

Another vital component for beaming power back to earth is a wireless power transmitter. This involves the use of antennas and rectennas which connect the Earth and power system in space using microwave radio frequency or lasers.

Two additional technologies required for SSP include reusable Earth-to-orbit space launch systems and efficient reusable in-space transportation systems to move the platform components from low Earth orbit.

Lunar solar power

Although the concept of collecting sunlight from satellites has been studied in some detail over the years, there are alternative approaches to solar power.

"The concept of collecting sunlight in space and transmitting it back to Earth is not new."

David Criswell, director of the Institute for Space Systems Operations at the University of Houston has been an advocate for obtaining solar power from the moon for many years and has proposed the large scale construction of solar collectors on the lunar surface.

He explained how this concept would work, if deployed: "Lunar space power bases, augmented by fields of solar collectors just across the edge of the moon, would continually collect solar power over the course of lunar day / night cycle.

"A power base converts the solar electricity, as available, into many beams of microwaves. A given beam is then created by all the power plots within the power base and directed to a field of rectifying antennas on Earth."

A full eclipse of the moon about once a year can cut off solar power for up to three hours, but supplemental solar power can be provided to the LSP bases via solar mirrors in orbit during this period. This eliminates the need for power storage.

Economical feasibility

As of 2010, the fundamental research to achieve technical feasibility for solar power satellites was accomplished, according to the First International Assessment of Space Solar Power, but whether these systems are launched into space depends on the availability of adequate budgets.

The current Nasa Institute of Advanced Concepts solar power programme includes participation from the US, Japan and Europe, with a total scope of more than twice Nasa's investment. Mankins believes in order to mature and demonstrate the technologies needed, an international project team, comprising government agencies, various industrial firms and universities will be required.

He said: "This approach mitigates risks and costs for all participating organisations. As for space launch, once a major demonstration (a pilot plant) is accomplished, the market case for affordable and reusable launch vehicles should be firmly established, and investments to develop such systems should be possible."

Criswell argues the lunar solar power system is projected to be, by far, the least expensive option for providing sufficient electric power to Earth to enable sustainable global prosperity.

"In a well run programme it will break-even at a cost of approximately $500 billion and could do so within 12 to 15 years," he said.

"The working goal is to provide everyone on Earth with 2 kWe/person or ten billion people with a global total of 20 TWe (teraWatts-electric)."

Global space power plans

"There are many reasons why space solar power (SSP) could be a key contender in meeting our global energy needs."

Japan is currently the only country with a focused solar power satellite plan. In fact, space power is one of the nine official goals of the Japanese space programme. The country's space agency is planning to construct a solar power station in space and use it to beam energy down to earth using lasers by 2030.

Other organisations around the world, however, are exploring space solar power concepts, including Astrium, a subsidiary of the European Aeronautic Defence and Space Company.

This firm is vowing to put its own solar demonstration satellite into orbit by the decade's end, according to announcements made in 2010.

Meanwhile, the US and India are making pledges to collaborate on a space-based solar programme, an idea initiated by the Institute of Defense Studies and Analyses. A report prepared by Peter Garretson, a US Air Force lieutenant colonel, called for the governments of India and the US to initiate this project and make the space-based solar energy a commercially viable business venture by 2025.

The Chinese have also committed to the development of SSP this year. Speaking at the China Energy Environment Summit in August, Wang Xiji, a space technology pioneer for the China Academy of Sciences, described a study on space solar power completed a month earlier by the academy.

Another very important point that Xiji made was that whoever takes the first mission to launch clean, renewable energy in space, will be the world leader. The race is on.

Transmitting power from space involves using antennas and rectennas.
John Mankins, a 25-year Nasa veteran.
Artist's concept of a Solar Power Satellite in place.
David Criswell, director of Institute for Space Systems Operations at University of Houston.