Test flight for possible Mars craft
A spacecraft that could one day take astronauts to Mars will undergo an historic unmanned test flight today.
The Orion craft, launched into orbit on a Delta IV heavy-lift rocket from Florida, will circle the Earth twice before re-entering the atmosphere at 20,000 mph.
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.
Even though the American space agency Nasa's new spacecraft bristles with the latest technology, it bears a strong resemblance to the Apollo command module that carried Neil Armstrong to the moon in 1969.
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.
Programme manager Mark Geyer said: "We're going to test the riskiest parts of the mission. Ascent, entry and thinks like fairing separations, Launch Abort System jettison, the parachute, plus the navigation and guidance - all those things are going to be tested.
"Plus, we'll fly into deep space and test the radiation effects on those systems."
Orion will launch from Cape Canaveral Air Force Station on the end of a Delta IV Heavy, the largest US rocket currently in service.
Three RS-68 engines will produce about two million pounds of thrust at lift-off.
The plan is for Orion to splash down in the Pacific off the coast of Baja California.
Unlike the Apollo module, which carried three astronauts, Orion is designed to carry a crew of four.
Measuring 16.5 feet across, it is larger than Apollo which had a diameter of 12.8 feet.