Gigantic satellites orbiting the Earth, equipped with solar cells, could collect enough energy from the sun every year to power the world seven times over. Beaming the energy down to Earth in the form of microwaves or a laser, the satellites would provide energy which would be gathered in antennas on the ground and then converted to electricity.

It may sound like a far-fetched idea, but researchers from the National Security Space Office (NSSO) say that the plan is technologically feasible, and could provide more energy than could fossil fuels, wind and nuclear power combined. They have recently presented their findings to the US government, recommending that the government spend $10 billion over the next 10 years to build a test satellite capable of electromagnetically beaming 10 megawatts of electric energy down to Earth.

"A single kilometer-wide band of geosynchronous earth orbit experiences enough solar flux in one year (approximately 212 terawatt-years) to nearly equal the amount of energy contained within all known recoverable conventional oil reserves on Earth today (approximately 250 TW-yrs)," according the report. "This far exceeds the projected 30TW of annual demand in mid-century."

The "space-based space power" (SBSP) construction would consist of kilometer-sized solar panel arrays, which could operate at night and during cloudy conditions.

The report explains that there are a couple ways the apparatus could work. The solar collectors could be places in one of three Earth orbits (geostationary, medium-Earth, or low-Earth) or could even be placed on the moon. These collectors could capture solar energy either by photovoltaic or solar dynamic methods. Finally, the collected energy could be beamed down to Earth by either coherent visible or infrared light.

"In the vicinity of Earth, every square meter of space receives 1.366 kilowatts of solar radiation, but by the time it reaches the ground, it has been reduced by atmospheric absorption and scattering; weather; and summer, winter and day-night cycles to less than an average of 250 watts per square meter. Space-Based Solar Power offers a way to break the tyranny of these day-night, summer-winter and weather cycles, and provide continuous and predictable power to any location on Earth."

The report explains that an area in space receives 8-10 times the energy flux for the annual average compared with an equivalent area on the surface of the Earth, and as much as 30-40 times the energy flux in a given week than the same area located in a favorable place on the ground after considering day/night, summer/winter, and dust/weather cycles.

Even after losses in wireless power transmission, the reduced need for overcapacity and storage to make up for periods of low illumination translates into a much lower land usage vs. terrestrial solar for an equivalent amount of delivered energy.

One of the biggest technical challenges of the plan is in launching the satellite, which would have a mass of about 3,000 tons-more than 10 times that of the International Space Station. Such a feat would require the development of lower-cost space launches. Today the United States initiates less than 15 launches per year. Construction of a single SBSP satellite alone would require in excess of 120 such launches.

"SBSP cannot be constructed without safe, frequent (daily/weekly), cheap, and reliable access to space and ubiquitous in-space operations," the report states. "By lowering the cost to orbit so substantially, and by providing safe and routine access, entirely new industries and possibilities open up." These possibilities may include space tourism, manufacturing, lunar or asteroid resource utilization, and eventually settlement to extend the human race, the report suggests.

The concept of SBSP was actually suggested as early as 1968 by Peter Glaser of a company called Arthur D. Little. However, his design was estimated to cost about $1 trillion to build, and required hundreds of astronauts to construct the solar panels while in space. With advances in photovoltaics, electronics and robotics, which would reduce the cost and eliminate the need for humans to assemble the equipment in space, the idea emerged again about a decade ago.

In 1995, NASA researchers found that, though feasible, SBSP was still not competitive when measured against the $0.05/kWh price of electricity and $15/barrel price of oil prevalent at that time. But in the past few years, especially since 9/11, much as changed, from increased oil costs to wide concern over oil resources and politics, to rising demand and competition from Chinese and Japanese economies.

Over the past three decades, the report details, NASA and the DOE have collectively spent $80 million in sporadic efforts studying this concept (by comparison, they note that the U.S. government has spent approximately $21 billion over the last 50 years continuously pursuing nuclear fusion). In this latest analysis, which took place over the past six months, more than 170 academic, scientific, technical, legal, and business experts around the world contributed, largely through e-mail and online communication.

The NSSO report emphasizes that the scheme would be economically viable, with paybacks as early as one year after implementation (not considering preliminary R&D).

"SBSP could be utilized to split hydrogen from water and the carbon monoxide (syngas) from carbon dioxide which can then be combined to manufacture any desired hydrocarbon fuel, including gasoline, diesel, kerosene and jet fuel," the report said.

"When all indirect and support costs are included, it is estimated that the DoD [Department of Defense] currently spends over $1 per kilowatt hour for electrical power delivered to troops in forward military bases in war regions. The fully burdened average price of fuel for the Army exceeds $5 a gallon. For Operation Iraqi Freedom, the estimated delivered price of fuel in certain areas may approach $20 a gallon."

The report also addresses the impact on Earth of beaming all that energy down. The researchers explain that microwave-receiving rectennas allow more than 90% of ambient light to pass through, but absorb almost all of the beamed energy. This means that the method generates less waste heat than terrestrial solar systems because of greater coupling efficiency, and also that the area underneath the rectenna can continue to be used for agricultural or pastoral purposes. In some cases, if desired, land in colder regions could even use some of the extra energy to maintain crops year-round.

And if you remember that just a year ago, a scientist named Roger Angel had a multi-billion-dollar idea to launch a "solar shade" to protect the Earth from additional sunlight, the NSSO report assures that its design won't have negative effects on global warming.

"While it may seem intuitively obvious that SBSP introduces heat into the biosphere by beaming more energy in, the net effect is quite the opposite," the report says. "Fossil fuel burning emits large amounts of waste heat and greenhouse gases, while terrestrial solar and wind power also emit significant amounts of waste heat via inefficient conversion. Likewise, SBSP also has solar conversion inefficiencies that produce waste heat, but the key difference is that the most of this waste heat creation occurs outside the biosphere to be radiated into space.

"The losses in the atmosphere are very small, on the order of a couple percent for the wavelengths considered. Because SBSP is not a greenhouse gas emitter (with the exception of initial manufacturing and launch fuel emissions), it does not contribute to trapping action and retention of heat in the biosphere."

For now, it seems the two biggest players in the alt-energy "race" would be--as the NSSO report puts it--Manhattan and Apollo.

More info:

Space-Based Solar Power As an Opportunity for Strategic Security

SBSP Blog

New Scientist



Lisa Zyga

Science Blogger

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