"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 fueling 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 Dec. 4 from nearby Cape Canaveral Air Force Station.
United Launch Alliance is jointly owned by Lockheed Martin Corp and Boeing Co.
In December Orion will be flown to an altitude of about 3,600 miles (5,800 km) 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 20,000 mph (32,000 kph). At that speed, Orion's thermal protection system should heat up to about 4,000 degrees Fahrenheit (2,200 degrees Celsius), proving the shield can protect astronauts returning from the moon and other deep-space destinations.
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 U.S. 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 U.S.-based commercial space taxi is also under way. The contenders are privately owned Space Exploration Technologies, also known as SpaceX, privately owned Sierra Nevada Corp 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 program. NASA has already spent about $9 billion developing Orion.