Cape Canaveral - A Nasa spacecraft designed to one day fly astronauts to Mars rolled out of its processing hangar at the US space agency's Kennedy Space Centre in Florida on Thursday to be prepared for a debut test flight in December.
"This is a pretty historic moment for us," Scott Wilson, Nasa's Orion production operations manager, told reporters as workers prepared to move the capsule to a fuelling depot. "This marks the end of the assembly process for the spacecraft."
An unmanned version of the gumdrop-shaped Orion capsule, which has been under construction for three years, is due to launch aboard a United Launch Alliance Delta 4 Heavy rocket on 4 December from nearby Cape Canaveral Air Force Station.
United Launch Alliance is jointly owned by Lockheed Martin and Boeing.
In December Orion will be flown to an altitude of about 5 800km from Earth, 14 times farther away than the International Space Station.
The capsule will then careen back toward the planet, slamming into the atmosphere at 32 000km/h. At that speed, Orion's thermal protection system should heat up to about 2 200°C, proving the shield can protect astronauts returning from the moon and other deep-space destinations.
Orion is part of Nasa's follow-up programme to the now-retired space shuttles that will allow astronauts to travel beyond the International Space Station, which flies about 418km above Earth.
A test flight with crew aboard is set for 2021. Nasa intends to use the rocket and Orion to fly astronauts to an asteroid that has been robotically relocated into a high orbit around the moon. Eventually, the US space agency wants to fly a four-member crew to Mars.
Nasa has been out of the human space launch business since the shuttle program ended in 2011.
The agency currently buys rides for space station crew members aboard Russian Soyuz capsules.
A heated three-way competition to build a US-based commercial space taxi is also under way. The contenders are privately owned Space Exploration Technologies, also known as SpaceX, privately owned Sierra Nevada and Boeing.
Work on the Orion deep-space capsule, built by Lockheed Martin, began more than a decade ago under Nasa's defunct Constellation moon programme. Nasa has already spent about $9bn developing Orion.