Dreams of Sailing Through Space
The National Aeronautics and Space Administration has announced that the Planetary Society, founded by scientist and author Carl Sagan, is set to build and fly a series of solar-sail spacecraft, dubbed LightSails, first in orbit around Earth and then into deeper space, in the next three years. The beauty of LightSails is that they are powered by sunshine, which carries both energy and momentum; unlike rocket fuel, this gentle force fires continuously.
Over time, a big enough sail, perhaps a mile on each side, could reach speeds of hundreds of thousands of miles an hour, fast enough to traverse the solar system in five years. Riding the beam from a powerful laser, a sail could even make the journey to another star system in 100 years, a human lifespan.
Dr. Louis Friedman, director of the Planetary Society, a worldwide organization of space enthusiasts, says eventual passengers will likely be robots or human genomes encoded on a chip, due to the need to keep the craft light, like a giant cosmic kite. In principle, it could tack like a sailboat. Japan is already testing solar sails deployed from satellites or rockets, although none are traveling anywhere yet.
These are visions for the long haul, advises Freeman Dyson of the Institute for Advanced Study in Princeton, New Jersey. He remarks: “Think centuries or millennia, not decades.”