Space-sailing anyone? British author Arthur C. Clarke described the concept of using massive solar sails to propel a spacecraft in the 1964 short story Sunjammer, also known as The Wind from the Sun.
'Hold your hands out to the sun,' says John Merton in the story. 'What do you feel? Heat, of course. But there's pressure too - though you've never noticed it, because it's so tiny.
'Over the area of your hands, it only comes to about a millionth of an ounce. But out in space, even a pressure as small as that can be important - for it's acting all the time, hour after hour, day after day. Unlike rocket fuel, it's free and unlimited. If we want to, we can use it; we can build sails to catch the radiation blowing from the sun.'
When the story was published, the notion of sunbeam-powered spacecraft-propulsion must have seemed as implausible as, well, a global network of personal computers. Solar sails have appeared in other works of fiction, including the novel Planet of the Apes (1963) by French novelist Pierre Boulle; the Japanese animated film Odin: Photon Space Sailer Starlight (1986) and George Lucas' Star Wars Episode II: Attack of the Clones (2002). But the idea was first suggested by German astronomer Johannes Kepler, best known for his laws of planetary motion, in the 17th century. Russian rocket scientist Friedrich Zander again proposed it in the late 1920s.
A United States-based media company, Cosmos Studios, and The Planetary Society, a US non-profit foundation co-founded by author and astronomer Carl Sagan, tried to turn it into reality with the US$4 million Cosmos 1 project. An unmanned solar sail craft, Cosmos 1 was launched in June 2005 from a submarine in the Barents Sea. But the Russian rocket carrying it failed.
But thanks to Nasa, the dream continues. The US space agency foresees the use of solar sail ships for deep-space exploration, with rockets for short-haul travel. There's next to no friction in space so a solar sail could move a ship faster than rocket propulsion, and it could keep travelling forever. Nasa has ploughed about US$2 million into building and launching the NanoSail-D, the first spacecraft to harness solar pressure as a primary means of manoeuvring. It was designed to unfurl four gossamer wings from its pod in space. The kite-shaped plastic-and-aluminium sail would have about 9 sqmetres of sunlight-catching surface.
