Scientists are looking for ways to propel spacecraft with less fuel than a rocket uses. The solar sail intrigues many because it requires no fuel at all.

In the late 1860s the theory of electromagnetism, first described by James Clerk Maxwell, defined light as a packet of energy called a photon. These photons have characteristics both of a wave and a particle, meaning at times they can behave like either, and they have energy and momentum when they move. The Russian space pioneer Konstantin Tsiolkovsky imagined that some day large thin sheets could be spread out in space to capture photons, which would push the reflective sail along as they bounced off it.

The National Aeronautics and Space Administration (NASA) has studied solar sailing. They launched small metal needles into the atmosphere high above the earth and found that sunlight altered their orbit. Using this discovery...