WASHINGTON — As the last man to walk on the moon prepared to fly back to Earth in 1972, astronaut Eugene Cernan echoed the words of the first, pledging with Neil-Armstrong-like grandiosity that “we shall return, with peace and hope for all mankind.” He later predicted that humans would reach Mars by the end of the 20th century.

Now Cernan admits: “I was a little off on my timing.”

Forty-two years after Cernan’s Apollo 17 mission touched down, not a single person has walked on the moon. A Mars landing is surely decades away, at best. And not a single spaceship designed to carry astronauts has left low Earth orbit.

But Thursday morning, NASA is scheduled to take what it calls a huge step toward advancing the nation’s human space flight program, with the much-anticipated first test flight of the Orion spacecraft.

A SHORT, UNMANNED FLIGHT

If all goes according to plan, the uncrewed Orion, manufactured by Bethesda, Maryland-based Lockheed Martin, would blast off at 7:05 a.m. EST from Cape Canaveral, Florida., orbit the Earth twice, hitting an altitude of about 3,600 miles above the surface of the planet. That’s farther than any spacecraft designed for humans has gone in more than 40 years.

Even though it is expected to last just 4.5 hours and won’t have people on board, the test flight “is a big deal,” NASA Administrator Charlie Bolden has said.

William Hill, a top NASA official, recently told reporters that the test flight is “absolutely the biggest thing that this agency is going to do this year.”

Unlike the capsules being developed by SpaceX and Boeing that would ferry astronauts and cargo to the International Space Station, Orion is designed to go deep into space, “farther than humans have ever traveled,” according to NASA. The test flight alone would go 15 times farther than the space station.

But NASA and Lockheed have grander plans for the Orion, which resembles prior capsules such as the Apollo, but which officials say is vastly more advanced.

Sometime in the 2020s, NASA plans to capture an asteroid with a robotic spacecraft, then drag it to the moon’s orbit where it would connect with the Orion. Astronauts would then be able to take samples from the asteroid.

The big target, however, remains Mars. And Thursday’s test flight will help “put Mars within the reach of astronauts in the 2030s,” NASA says.

MARS A PRIORITY

But the asteroid mission has been derided as a stunt. “That’s a dumb idea to start with. It’s nothing but talk,” Cernan said. The program for Mars has been fitful, and is to many a fantasy, especially considering that since the retirement of the space shuttle three years ago, the U.S. has not been able to send its astronauts to space from American soil.

“Forty-two years ago I walked on the moon,” Cernan said. “And today we can’t even put an American in space on American hardware. That’s heartbreaking. It’s disappointing. I cannot believe or imagine that we allowed this happen. . . . I anticipated we’d be well on our way, by golly, by now to Mars and there’s no reason we couldn’t have been.”

Orion originally grew out of a George W. Bush administration program, called Constellation, to return to the moon by 2020. The Obama administration killed Constellation and made Mars the priority over a return to the moon because, as President Barack Obama said at the time, “We’ve been there before.”

In the nearly 10 years since it first awarded Lockheed to contract to build Orion, NASA has spent more than $9 billion on the program.

Thursday’s mission will use a Delta IV heavy rocket.