Dec. 3, 2014: The NASA Orion space capsule is seen atop a Delta IV rocket ready for a test launch at the Cape Canaveral Air Force Station.(AP)

CAPE CANAVERAL, Fla. With the imminent debut of its Orion spacecraft, NASA is on a high not felt since the space shuttle days.

Shuttle veterans, in fact, are leading the charge in Thursday morning's two-orbit, 4-hour test flight, meant to shake out the capsule before astronauts climb aboard eventually, perhaps, to visit Mars.

"We haven't had this feeling in a while, since the end of the shuttle program," said Mike Sarafin, the lead flight director stationed at Mission Control in Houston. "Launching an American spacecraft from American soil and beginning something new, in this case exploring deep space."

Orion is set to fly farther than any human-rated spacecraft since the Apollo moon program, aiming for a distance of 3,600 miles, more than 14 times higher than the International Space Station.

That peak altitude will provide the necessary momentum for a 20,000-mph, 4,000-degree entry over the Pacific. Those 11 short minutes to splashdown is what NASA calls the "trial by fire," arguably the most critical part of the entire test flight. The heat shield at Orion's base, at 16.5 feet across, is the largest of its kind ever built.

Navy ships were stationed near the recovery zone off the Mexican Baja coast.

"It's an exciting time," Jeff Angermeier, ground support mission manager, said from Florida's Kennedy Space Center. "You can feel the buzz."

An estimated 26,000 guests were expected to jam Kennedy for the sunrise launch, as well as 650 journalists. (Actually, the unmanned rocket will blast off from the adjoining Cape Canaveral Air Force Station.) The space center press site was packed Wednesday with out-of-town reporters not seen here since the last shuttle flight in 2011.

NASA's Orion program manager, Mark Geyer, puts the capsule's inaugural run on a par with the formative steps of Apollo and the space shuttles.

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NASA set to launch much anticipated Orion spacecraft