Story highlights New spaceship Orion is "go" for test flight

Launch is set for 7 a.m. ET Thursday

Orion will orbit Earth twice and will splash down in the Pacific

It's the biggest countdown for NASA since the shuttle era ended in 2011. The space agency's new Orion spacecraft is scheduled to lift off on an uncrewed test flight at 7:05 a.m. ET Thursday from Space Launch Complex 37 at Cape Canaveral, Florida.

"We haven't had this feeling in awhile, since the end of the shuttle program," Mike Sarafin, Orion flight director at Johnson Space Center, said in a preflight briefing on Wednesday. He said it's the beginning of something new: exploring deep space.

Orion looks like a throwback to the Apollo era, but it is roomier and designed to go far beyond the moon : to an asteroid and eventually to Mars.

"It is, I think, consistent with those -- the beginning of shuttle and beginning of Apollo," said Mark Geyer, NASA Orion program manager. "I think it's in the same category."

When it becomes fully operational, Orion's crew module will be able to carry four people on a 21-day mission into deep space or six astronauts for shorter missions. By comparison, the Apollo crew modules held three astronauts and were in space for six to 12 days. Orion's crew module is 16.5 feet in diameter and Apollo was 12.8 feet in diameter, NASA said.

Photos: Photos: Orion -- NASA's next giant leap Photos: Photos: Orion -- NASA's next giant leap Orion -- NASA's next giant leap – NASA's Orion spacecraft, atop a Delta 4-Heavy rocket, lifts off on its first unmanned orbital test flight from Cape Canaveral, Florida, on Friday, December 5. NASA hopes Orion will usher in a new era: eventual human exploration of deep space. Hide Caption 1 of 9 Photos: Photos: Orion -- NASA's next giant leap Orion -- NASA's next giant leap – Orion sits on top of a Delta IV Heavy rocket on the launchpad at Cape Canaveral on Wednesday, December 3, waiting for its first test flight. Orion is designed to take humans to an asteroid and on to Mars, but its first flight will not carry a crew. Hide Caption 2 of 9 Photos: Photos: Orion -- NASA's next giant leap Orion -- NASA's next giant leap – NASA's first completed Orion crew module sits atop its service module at Kennedy Space Center before being wrapped in protective panels and stacked on a Delta IV Heavy rocket for its first test flight. Hide Caption 3 of 9 Photos: Photos: Orion -- NASA's next giant leap Orion -- NASA's next giant leap – Workers finish wrapping Orion in protective panels for its first flight. The panels protect the crew module from sound and vibration during launch. Hide Caption 4 of 9 Photos: Photos: Orion -- NASA's next giant leap Orion -- NASA's next giant leap – Workers check Orion after its last major assembly operations are completed -- the installation of protective panels around the spacecraft just below the Launch Abort System tower. Hide Caption 5 of 9 Photos: Photos: Orion -- NASA's next giant leap Orion -- NASA's next giant leap – Orion is wheeled past the iconic Vehicle Assembly Building at NASA's Kennedy Space Center on November 11, 2014, on its way to Launch Complex 37 at Cape Canaveral Air Force Station. Hide Caption 6 of 9 Photos: Photos: Orion -- NASA's next giant leap Orion -- NASA's next giant leap – Orion is mated with a United Launch Alliance Delta IV Heavy rocket, the rocket that will carry it into space on its first test flight. Hide Caption 7 of 9 Photos: Photos: Orion -- NASA's next giant leap Orion -- NASA's next giant leap – Orion sits on the launchpad at Cape Canaveral after being stacked on the rocket. Orion will take crews farther from Earth than any spacecraft since Apollo. Hide Caption 8 of 9 Photos: Photos: Orion -- NASA's next giant leap Orion -- NASA's next giant leap – Orion will be the first U.S. spacecraft since the Apollo-era to splash down in the ocean. In this photo, crew members on the USNS Salvor pull a test version of the spacecraft out of the ocean using a crane. Hide Caption 9 of 9

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Orion is expected to take up its first crew in 2021.

During this test flight, Orion will climb to an altitude of 3,600 miles (15 times higher than the International Space Station) and will orbit Earth twice. Four and half hours later, it will splash down in the Pacific Ocean about 600 miles off the coast of Baja California. Two U.S. Navy ships, the amphibious transport dock ship USS Anchorage and the Military Sealift Command rescue and salvage ship USNS Salvor, will help NASA recover the capsule.

NASA said there haven't been any major issues with the countdown. The vehicle is "extremely clean" and "we're ready to go," said Geyer.

The weather forecast for liftoff also is good, with a 70% chance of acceptable launch conditions, according to Kathy Winters, a U.S. Air Force weather officer. "It looks pretty promising weather-wise for launch," she said.

Winters said there may be some scattered clouds, but because the launch window will be open for two hours and 39 minutes, mission managers have some wiggle room if rain moves in. The temperature at launch time should be around 72 degrees Fahrenheit.

With mostly clear skies in the forecast, residents along Florida's east coast should be able to see the contrail from the huge Delta IV Heavy rocket that will carry Orion into orbit. The rocket is provided by United Launch Alliance, one of the private partners helping NASA with this launch. Eventually, NASA will use its own Space Launch System, which is under construction.

Once in orbit, Orion should send back some amazing pictures of Earth, NASA said. If the weather cooperates, NASA said a drone will provide a live video feed of the splashdown.

Though Orion's first flight won't have people on it, it won't go up empty. It will carry the names of more than a million people packed on a dime-sized microchip.

"Sesame Street" is sending up some mementos to inspire students about spaceflight, including Cookie Monster's cookie and Ernie's rubber ducky.

Also going up: an oxygen hose from an Apollo 11 lunar spacesuit and a small sample of lunar soil. A Tyrannosaurus rex fossil from the Denver Science Museum will be on board and lockers will be filled with flags, coins, patches, poetry and music.

In one more throwback to the Apollo-era, NASA veteran Gene Kranz will be a VIP in Mission Control at Johnson Space Center in Houston when Orion is launched. Kranz was flight director for Apollo 11 during the first landing on the moon and he was flight director for the return of the Apollo 13 crew.

"I look forward very much to having him watch the team in action," Serafin said.