WASHINGTON (Reuters) - NASA gave visitors to the National Mall in Washington a peek at a full-size mock-up of the spacecraft designed to carry U.S. astronauts back to the moon and then on to Mars one day.

A full-size mockup of the crew module for the Orion Crew exploration vehicle is displayed on the National Mall near the Capitol (background) in Washington March 30, 2009. The Orion will become America's primary vehicle for human space exploration, replacing the space shuttle after it is retired in 2010. REUTERS/Kevin Lamarque

The U.S. Navy-built Orion crew exploration vehicle will replace the space shuttle NASA plans to retire in 2010, and become the cornerstone of the agency’s Constellation Program to explore the moon, Mars and beyond.

“We’re just very proud to build this, do some testing and demonstrate to America that we’re moving beyond the space shuttle onto another generation of spacecraft,” said Don Pearson, project manager for the Post-Landing Orion Recovery Test or PORT.

NASA plans to use Orion to carry astronauts to the International Space Station by 2015. The capsule will rotate the crew at the station every six months “to work out the kinks” before heading to the moon and Mars, Pearson said.

Trips to the moon are scheduled for 2020, while a journey to Mars is believed possible by the mid-2030s.

The design of Orion was based on the Apollo spacecraft, which first took Americans to the moon. Although similar in shape, Orion is larger, able to carry six crew members rather than three, and builds on 1960s technology to make it safer.

‘WE WANT TO GO TO MARS’

Orion is named for a bright constellation that got its designation from a hunter in ancient Greek mythology.

“The reason we’re doing all of this is because we want to go to Mars,” Pearson said.

But a round trip to the red planet would require three years -- six to nine months to get there and much of the rest of the time waiting for the planets to realign to allow for entry back to Earth.

“We’re not confident in our technology yet to be able to last for three years without things breaking that are unrepairable,” Pearson said.

So NASA plans to first take several trips to the moon, a journey of just three days. Each visit will last six months while astronauts set up a campsite and practice the things they want to do on Mars.

“That’s really the goal -- to put humans on Mars, and going to the moon is our testing ground in order to do it,” Pearson explained.

The $2 million PORT project will make sure that crew members can be rescued from the choppy waters of the Atlantic in case of an emergency requiring an aborted launch, using the full-scale, 18,000-pound (8,000 kg) model of Orion.

On April 6, the capsule will be dumped into the Atlantic Ocean off the coast of Florida, using one of the ships that usually recovers rocket boosters from shuttle launches. Instruments within the capsule will measure the acceleration and tilting astronauts would experience upon landing in waves.

Contractors for the project include Lockheed Martin Space Systems Corporation of Denver and Orbital Sciences Corp of Dulles, Virginia.

Over the summer, flight doctors will analyze the data to ensure it does not make astronauts too queasy.

Crew seats will be installed in the model this summer as well to allow astronauts to practice getting out of the capsule on their own while bouncing in big waves.