No astronauts will be on board the capsule when it launches aboard the United States' largest rocket, the Delta IV Heavy made by United Launch Alliance, but engineers will be keenly watching to see how it performs during the four-and-a-half hour flight.
The launch marks the first of a US spacecraft meant to carry people into deep space since the Apollo missions that brought men to the Moon in the 1960s and 1970s.
With no American vehicle to send humans to space since the space shuttle was retired in 2011, some at NASA said the Orion launch has re-energized the US space program, long constrained by government belt-tightening and forced to rely on costly rides aboard Russian Soyuz spacecraft to reach the International Space Station in low-Earth orbit.
"We haven't had this feeling in awhile, since the end of the shuttle program, (of) launching an American spacecraft from America's soil and beginning something new," said Mike Sarafin, lead flight director at NASA's Johnson Space Center in Houston.
Tourists and space enthusiasts lined the area known as Florida's Space Coast to see the powerful rocket blast off at sunrise, and 27,000 guests were at Kennedy Space Center for a close up look at the rocket, NASA spokesman Mike Curie said.
Potential future missions for Orion, which is designed to fit four people at a time, include a trip to lasso an asteroid and a journey to Mars by the 2030s.
"Thursday is the beginning of that journey, testing key systems - the riskiest systems I would say for Orion – before we have any people on board," said Mark Geyer, program manager for Orion.
The launch at 7:05 am (1735 IST) from Cape Canaveral, Florida, aims to propel 739,000 kilograms of spacecraft, rocket and fuel straight to space, where the capsule will make two laps around the Earth before splashing down in the Pacific Ocean.
The first orbit will be about as high as the International Space Station, which circles at an altitude of about 430 kilometers, but the second will soar 15 times higher, to an apogee of 5,800 kilometers above the Earth.
The chief contractor of the Orion capsule is Lockheed Martin. The spacecraft was first designed to take humans to the Moon as part of NASA's Constellation program, which was cancelled by President Barack Obama in 2010, in favor or seeking new destinations in deep space.

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