Solar sails pick up speed

Two trials of spacecraft have successfully unfurled their solar sails, and demonstrated that radiation from sunlight can power them through interplanetary space.

Solar sails use photons from the Sun to propel spacecraft at high speeds. On 20 January, the small lightweight spacecraft NanoSail-D deployed a 10-square-metre gleaming sail in low-Earth orbit.

Shortly after, on 26 January, engineers at the Japan Aerospace Exploration Agency (JAXA) announced the extension of their solar-sail mission IKAROS. Launched in May 2010, IKAROS flew past Venus in December last year, and the mission will continue until March 2012.

"Both of these are very good technological advances and help give confidence to solar sailing," says Louis Friedman, executive director of the Planetary Society, a non-profit organization for space-based research based in Pasadena, California, that is hoping to launch its own solar sail by the end of the year.

Unlimited power

Solar sails are driven forwards when photons from the Sun strike their large, thin sheets, imparting a small force. Unlike other propulsion methods, which require a spacecraft to carry fuel, the power source of a solar sail is essentially unlimited. Because they experience no friction in space, solar sails build up a great deal of thrust, and researchers hope that they could eventually be used to reach other planets or even other stars.

In contrast to IKAROS, NanoSail-D was designed to travel closer to home. Launched into low-Earth orbit, it will experience drag on the sail as it skims the planet's upper atmosphere. Within a few months, the spacecraft should slow sufficiently to re-enter and burn up. The technology could one day be attached to decommissioned satellites to slow them down and assist in de-orbiting, says Dean Alhorn, an engineer at NASA's Marshal Spaceflight Center in Huntsville, Alabama, and principal investigator of the NanoSail-D mission.
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