Increasing oil prices and environmental conscientiousness have generated a commensurate spike in interest in renewable energy sources. Most technologies, however, are ill-suited to providing large-scale, base-load power. Solar, wind, hydroelectric, and geothermal power all rely on specific environmental or geographic conditions that are intermittent or uncommon in nature. Furthermore, the places where these conditions do occur are often far from the population centers where power is needed most. Of the mature renewable energy systems, solar is the most widely applicable, because the sun, to a greater or lesser extent, shines everywhere. But even photovoltaic solar power systems cannot provide universal base-load power. Subject to the vagaries of weather, season, and the diurnal cycle, photovoltaic systems are typically regarded as a supplementary system, at best.
There is one place, however, where the power of the sun remains unattenuated by the messy conditions on the surface and uninterrupted by the day–night cycle. The Earth's orbit receives a solar flux of approximately 1,400 watts per square meter, and a space-based solar power system would take full advantage of this energy source. By the time the sun's rays reach the planet's surface, the solar flux is reduced, on average, to a quarter of this value.
The centerpiece of a fully developed space solar power system would be a huge satellite, with mirrors or collecting surfaces measured in square kilometers, located in geostationary orbit -- approximately 22,236 miles (or 35,786 kilometers) directly above the equator, where satellites travel at the same speed as the Earth's rotation and thus appear to be motionless. Using photovoltaic panels, this satellite would collect incident solar radiation to generate electricity and then use onboard equipment to convert the power thus generated into an electromagnetic beam. Most proposed architectures call for either an infrared or microwave beam. This beam would be aimed at a receiver on the ground, where it would be converted back into usable electricity and then fed into the grid for consumption. The beam would be dispersed over a large receiving array, so birds and aircraft would be able to safely fly through it.
Not only would power delivered in this way generate no greenhouse gases, but it would be consistent, reliable, and scalable. Most of all, however, such a system would be flexible. A space solar power system with only two or three satellites would be capable of directing gigawatts of power to virtually any point on the globe.
By nature of its basic characteristics, the system has implications that extend far beyond national energy and industrial policy. Its ability, in principle, to deliver strategically significant levels of electrical power almost anywhere in the world has important international security ramifications. There are many ways that space-based solar power could be used in novel security-oriented modes. From supporting friendly troops and providing disaster relief in the field, to propping up rogue regimes, the technology has the potential to offer those nations that develop it a powerful and flexible tool with fundamentally new, even transformative, applications.
An apt example is the recent civil war in Libya. If one or more NATO powers had had an operational space-based power system, they could have delivered sufficient energy for the rebels to maintain a significantly more complex infrastructure, even as the old regime's infrastructure was reduced to rubble by air strikes and general fighting. Despite the powerful new security capabilities that a space solar power system represents, the technology has received little attention in the academic literature outside of scientific and engineering circles.
Three phases of interest. Fantastic as the concept may seem, a space solar power system is not science fiction. In recent years especially, it has gained currency with several governments, notably China and Japan, and a number of new companies in the United States and abroad are dedicated to commercializing the concept. Furthermore, its constituent technologies are, overall, quite mature.
The full contents of this article are available in the January/February issue of the Bulletin of the Atomic Scientists and can be found here.