Nothing this big has ever been deployed in space

Les Johnson

"This will be humankind's first planned venture outside our Solar System," says Les Johnson, manager of Interstellar Propulsion Research at Nasa's Marshall Space Flight Center. "This is a goal that is among the most audacious things we've ever undertaken."

The dream is for an interstellar probe that will travel over 37 billion km (23 billion miles), which is about 250 times the distance between the Earth and the Sun.

This is first step to the stars and has an estimated trip time of 15 years.

To put this into context, if the distance from Earth to the Sun equalled 30 cm (one foot) then the distance to the nearest star would be about 80 km (50 miles).

Outer limits

Optimistically proposed for launch around the year 2010, the interstellar probe or precursor mission, as it has been called, would be the fastest spacecraft ever flown.

Travelling at 93 km per second (58 miles per second), it could cross the US in less than a minute.

That is five times faster than the Voyager spacecraft launched in 1977 to explore our Solar System's outer limits.

If launched in 2010, the probe would overtake Voyager in 2018, going as far in eight years as Voyager will have journeyed in 41 years.

Les Johnson says speed is the crucial issue for any interstellar mission.

Laser beams

"The difficulty is that rockets need so much fuel that they can't push their own weight into interstellar space. The best option appears to be space sails, which require no fuel," he said.

Les Johnson holds carbon fibre that could be used to make a space sail

He envisages ultra-thin, reflective sails that could be propelled through space by sunlight, microwave beams or laser beams just like the wind pushes sailboats on Earth.

Rays of light from the Sun would provide tremendous momentum to a gigantic structure. The sail being planned by Nasa would be 400 metres (1,320 ft) across.

"Nothing this big has ever been deployed in space. We think we know how to do it, but we're in the beginning phases of turning a concept into a real design," Johnson said.

Researchers are optimistic about recent breakthroughs with strong, lightweight composite materials. A leading candidate for sails is a low-density carbon fibre material.