Nasa is set to race back into space today on a 3billion mile journey to the only planet still unvisted – distant Pluto.
The £400million New Horizons mission – shown on the launchpad, right – will be the fastest spacecraft ever launched when it lifts off from Cape Canaveral in Florida.
The unmanned probe, which is the size of a piano, will zip past our Moon’s orbit in just nine hours compared to the three days it took Apollo astronauts more then 30 years ago.
But it will still take nearly ten years to reach the remote planet that is furthest out in the solar system and only discovered in 1930.
Space scientists hope the stunning success of the return of their Stardust capsule to Earth on Sunday will bode well for New Horizons mission.
It aims to find more pieces of the jigsaw that explain the origins of the planets in the few hours it will get to study Pluto as it zips by in 2015.
But Nasa faces anti-nuke protests today outside the space centre because the probe is carrying 24lb of radioactive plutonium to provide electrical power for the its instruments.
Pluto is too far away for solar panels to provide electricity. Light from the sun takes four hours to get there.
Nasa say there is only a one in 350 chance of an accident releasing plutonium on launch.
US Congress ruled out using nuclear-power to propel the spacecraft. Instead it will be launched at 6.24pm UK time using conventional fuel by an Atlas 5 rocket.
One of the boosters had to be replaced after being damaged by Hurricane Wilma in October.
Pluto is less that 1,450 miles wide – only two thirds the diameter of the moon. It has a bizarre atmosphere which freezes and collapses onto the surface when the planet is at its furthest from the sun.
Pluto has three tiny moons of its own. Many believe it is not a proper planet but one of a class of objects forming the Kuiper Belt – a band of icy worlds containing material unchanged since the birth of the solar system 4.5 billion years ago.
If anything delays today’s launch, Nasa will be desperate to launch before the end of the month. Otherwise the probe will miss a rendezvous with Jupiter within a year to send it like a slingshot on to Pluto.
Without that boost, the mission, 17 years in the planning, will take at least three years longer to reach Pluto.
New Horizons finally blasted off on January 19 after a two-day delay, firstly because of high winds at Cape Canaveral, then a day later when storms knocked out the mission control centre near Washington.

© Paul Sutherland. Unauthorised reproduction forbidden.