This January the Planetary Society, in cooperation with Cosmos Studios and Russia's Babakin Space Center in Moscow will launch Cosmos 1, a 3-foot-wide experimental "solar-sail" powered spacecraft. Once it reaches Earth's orbit, inflatable tubes will force the lightweight sail to fan out into its orbital form. The eight blades of the craft's beach umbrella-like sail are programmed to lock into position, and can then be manipulated to allow photons in the solar wind to propel the craft. In a test three years ago, Friedman's group launched a suborbital version of Cosmos 1 that never managed to open its two-bladed sail.
The concept of "sailing" using the sun's rays was first devised nearly 400 years ago by astronomer Johannes Kepler, who noticed that comets' tails are blown by an apparent solar wind. He theorized that the same force could be harnessed to propel space vessels. The solar sail designed by Friedman's group isn't really blown by solar winds; unlike a breeze which pushes the canvas of a traditional sail, light particles generate their force by striking the mirror-like surface of the ultra-thin sail and reflecting off it. This reflection creates a very tiny force (about the force of a postage stamp resting in your palm), but it is constant and, in the vacuum of space, can accelerate over weeks and months to reach velocities faster than any chemically fueled spacecraft to date.
Solar-sails and similar technologies have been fertile ground for science fiction authors for decades (one of the best such pieces is Poul Anderson's Tau Zero, about interstellar travellers on a Bussard ramscoop ship that runs into trouble), so as a science-fiction enthusiast it is very exciting to see this become reality.
NASA researchers at the Jet Propulsion Laboratory in Pasadena have been working on their own space sail concept and had planned to launch a probe that would zip around the outer solar system using the force of solar particles. A flight test of the craft had been scheduled for 2007, but was indefinitely postponed due to a lack of funding, according to JPL's Sarah Gavit.
Other scientists, meanwhile, are investigating a form of space sailing that wouldn't rely on direct energy from the sun. Robert Winglee of the University of Washington in Seattle says his concept could get people to Mars and back in an anstonishing three months, putting the planet well within reach (current technologies would take approximately two-and-a-half years). The shorter trip would also be much less expensive, because everything the astronauts need must be packaged (food, water, air, etc.) and propelled along with them. The new concept would deploy an intermediate space station that would beam a stream of plasma, or magnetized particles. The space station would use solar energy to generate the beam of magnetized particles from a nozzle about 100 feet wide, focusing the solar energy. By capturing these particles in its sail, the spacecraft would be propelled as the particles bounce from its surface. Winglee estimates the system could propel a craft to spectacular speeds of about seven miles per second (25,200 miles per hour). To put it another way, this craft powered by light would be able to travel around the earth's equator (25,050 miles) in less than an hour!
Although a solar-sail might be the fastest and cheapest idea available, it's unlikely to play a role in President Bush's mandate announced last January to send manned missions back to the moon and then on to Mars. Despite the speed and cost advantages, the science, says Friedman, is still far out.