A spacecraft that could one day take astronauts to Mars will undergo a historic unmanned test flight today.
The Orion craft below), launched into orbit on a Delta IV heavy-lift rocket from Florida, will circle the Earth twice before re-entering the atmosphere at 20,000mph.
It is the first mission since the Apollo moon landings to take a spacecraft built for manned flight into deep space beyond the limit of orbiting satellites.
During the 4.5-hour flight Orion will travel 3,609 miles from Earth, 15 times the distance to the International Space Station.
A key part of the mission will be to see how Orion's heat shield withstands the 2,200C heat of re-entry.
Nasa hopes to use Orion to put astronauts back on the moon by 2020 and take them to Mars in the 2030s. A midway mission to an asteroid is also on the cards.
Mark Geyer, the project manager, said: "We're going to test the riskiest parts of the mission. Ascent, entry and things like fairing separations, Launch Abort System jettison, the parachute, plus navigation and guidance - these things will be tested. We'll fly into deep space and test the radiation effects on those systems."
Orion will splash down in the Pacific off Baja California.