Special thanks to Dr. Louis Friedman, Executive Director of The Planetary Society, for his technical assistance.
In the 1970s, NASA scientists proposed sending a probe to Halley's comet that would be propelled by the pressure of sunlight against a giant solar sail. Although the proposal was rejected as being too risky and unproven, the idea of solar-sail-propelled spacecraft has endured. Numerous developments and tests of solar-sail materials have been conducted over the years, but no one had designed, successfully launched and sailed such a spacecraft.

In mid-April 2001, The Planetary Society, in collaboration with several Russian space organizations, will test launch the deployment mechanism for the first solar-sail mission, Cosmos-1, in a sub-orbital flight. If the test is successful, they will launch the Cosmos-1 spacecraft into Earth orbit in October 2001.

Photo courtesy The Planetary Society
Solar sails will use the sun's energy to propel spacecraft across the cosmos.

What is a solar sail? How can you use sunlight to move a spacecraft in outer space? In this edition of HowStuffWorks, we'll show you how solar sails work, take an in-depth look at the Cosmos-1 mission and find out what solar-sails mean for future space travel.