Many futuristic spaceships rely on variations of rockets for propulsion. But some of the most innovative designs are exploring new space technologies that are not rockets at all but will still allow us to travel through space. One such technology is the solar sail.
The purpose of solar sails is to harness solar energy to power spaceships. A ship would be fitted with a sail made of an extremely thin and reflective material. The sail would then propel the ship by catching photons of light emitted by the Sun. Although the entire force of these photons on a solar sail the size of a football field would only equal the weight of a marble, that tiny push could produce remarkable acceleration because there is no drag and no gravity in space. For its first sixty minutes in space, a solar-sail ship with the Sun at its back would cover only ten miles. But after a day it could travel at two-hundred miles an hour, and after eighteen days it would be hurtling along at a mile a second and still picking up speed.
Solar sails are attractive because they use simple hardware and a free source of energy. The one problem is designing a sail large enough and light enough to catch the enormous quantities of sunlight needed.
Rob Staehle, an engineer at the Jet Propulsion Laboratory in California who founded the World Space Foundation in 1979 in order to put a little adventure back into space exploration, has been focusing on designing such sails. He's had enough success to plan a solar sail race to the Moon.
Because the technology doesn't require billion-dollar budgets for development, it could play an important role in the future exploration of the solar system. Solar-sail ships could be used as supply ferries for a fraction of the cost of chemical or nuclear ships. This "rebel technology" could also potentially make space travel available to large numbers of ordinary people at reasonable cost.
Another non-rocket space technology currently being studied is tethers. Robert Forward, a leading expert on interstellar flight, and Chris Rupp, a scientist at NASA's Marshall Space Center, are two of the people pursuing the idea of space tethers as a replacement for retrorockets. The tether, a twelve-mile long line no thicker than a kite string but made of an extremely strong material called spectra, can hold ten times its weight (a twenty-pound spool can hold a two-hundred-pound load). Tethers offer a new way to drop, or de-orbit, payloads from space stations. They could be another rebel technology making space travel and work not only possible but affordable.
