NASA?s Marshall Space Flight Center is developing gigantic ?light sails? that could harness the gentle winds of solar radiation and drag an accompanying craft beyond the reaches of our solar system?. ?This will be humankind?s first planned venture outside our solar system,? said Les Johnson, manager of Interstellar Propulsion Research at the Marshall Center,  who thinks that recent advances in materials could see an old science fiction dream become a reality by the end of this decade. ?This is a stretch goal that is among the most audacious things we?ve ever undertaken?Imagine a parachute in reverse and you have the basic concept of a light sail spacecraft. A capsule containing a probe or human beings is tethered to an immense sheet of reflective material spread out towards the desired direction of travel. Solar radiation coming from behind the capsule moves past it and is captured by the sail. The minuscule impact of each photon transfers a tiny amount of kinetic energy to the craft, eventually resulting in forward momentum. Although the acceleration is none too dramatic, once the light sail is up and running, the speeds it can obtain make our current spacecraft look sluggish.

Other plans are in development for similar craft that would be powered by burst of microwaves or laser beams fired from orbiting satellites. Such interstellar probes will be the largest and fastest spacecraft ever built. The maiden interstellar voyage would probably be to our closest neighbouring system, Alpha Centauri. A journey of this distance dwarfs anything humankind has ever considered before. The light sail craft would need to travel tens of billions of kilometers just to get to the outer reaches of our solar system. Even then, its journey would just be beginning. It’s another 4.2 light years to the Centauri stars. Proposed for launch in a 2010 time frame, the stellar sailboat would be forging towards the stars at 93 km (58 miles) per second. That would make the trip from New York to Los Angeles last less than a minute. It?s also more than 10 times faster than the Space Shuttle?s orbital speed. At that rate, the craft would quickly overhaul the tiny Voyager probe, launched in 1977 to explore our solar system?s outer limits. (Voyager’s most recent encounter was with Neptune.) The 2010 light sail craft would need just 8 years to pass its predecessor, going as far in that time as Voyager would have journeyed in 41 years. Some physicists speculate that light-powered craft could eventually reach velocities equal to about 10% of the speed of light.