The idea occurred to German astronomer Johannes Kepler in the 17th century when he detected a comet flying across the night sky trailing what looked like a plume of fire.
If space had so much wind, why not build ships to sail the heavens?
Indeed. Last night a US filmmaker, an international association of space buffs and Russian aerospace organisations used a leftover Soviet ballistic missile to put the first "solar sail" into orbit.
This unusual device, which looks like a 6,500 sq-ft flower with eight triangular, mirror-like petals, does not use wind, as Kepler predicted. Instead, it is to show that sunlight's gentle push might one day enable a spacecraft to reach speeds far greater than anything achieved by a mere rocket. Deployed, the petals are about 1½ times the size of a basketball court.
"The design life for this mission is only a month," said Louis Friedman, project director for the venture known as Cosmos 1. "It could go longer, but not much. What we want to do is prove that it works - that we can increase orbit energy and make it fly higher."
Solar sails work on a relatively simple principle - that beams of light bouncing off a reflective surface will transmit a push to the surface, driving it forward. Although the force is tiny, it is also constant and cumulative. And in the vacuum of space, there is no atmospheric friction to slow it down.
Speed rises and eventually will build well beyond the 25,000 mph needed to free an object from Earth's gravity.
If they handle it properly, ground-based engineers can steer a solar sail back and forth in space, Friedman said, "tacking it, like a sailboat - although the physics are different".
Nasa in-space propulsion technology manager, Les Johnson, is overseeing two Nasa solar-sail projects expected to be ready after 2010.
Space visionaries talk about using sails to travel between the stars, but beyond Jupiter, sunshine is not strong enough to provide the impulse, making it necessary to develop some kind of earth or space-based laser or microwave "ray gun" to provide light as the sails move into deep space. This technology is decades away.
In the relatively near term, however, solar sails might offer tremendous advantages over conventional propulsion for satellites orbiting the sun closer in than earth. Friedman said he first began thinking about solar sails in the 1970s as a Nasa mission planner at the jet propulsion laboratory.
He was evaluating a proposal to use a solar sail to rendezvous with Halley's comet, an idea that was "way too audacious at the time", Friedman said, but fascinating enough for him to write a book about it.
In 1980, Friedman joined planetary scientist Bruce Murray and astronomer and author Carl Sagan in founding the Planetary Society, an international advocacy organisation dedicated to space exploration, based in Pasadena, California.
The society is leading the solar-sail project, funded by Ithaca, New York-based Cosmos Studios, a scientific documentary film and entertainment company headed by Sagan's widow, Ann Druyan.
The remaining partners are NPO Lavochkin, the Russian agency that designed the spacecraft, and the Russian Academy of Science's Space Research Institute. - (Los Angeles Times - Washington Post service)