Speaking at a White House event honoring Apollo 11, Buzz Aldrin, the second man to walk on the Moon, said he's "disappointed" with the progress America's space program has made over the past 50 years.

"[I'm] disappointed in the progress in the past 50 years," Aldrin said at the event held in the Oval Office. "We had a rocket, the Saturn 5. We have the [number one] rocket and spacecraft and they can’t get into lunar orbit. That’s a great disappointment to me."

NASA's Administrator Jim Bridenstine, who was also at the event, said the space agency is "working on it."

APOLLO 11'S MICHAEL COLLINS REFLECTS ON HISTORIC MOON LANDING: 'WE WERE JUST REGULAR ASTRONAUTS'

During the event, President Trump said that the Moon landing was "one of the greatest achievements ever," before adding America would eventually go to Mars, noting that, "From a defense standpoint, it's very important."

Trump asked whether astronauts could go straight to Mars without first going to the Moon, to which Bridenstine said no, that a gateway is needed to eventually journey to the Red Planet.

President Trump welcomed Aldrin, fellow Apollo 11 astronaut Michael Collins and family members of Apollo 11 Mission Commander Neil Armstrong to the White House on Friday to commemorate the 50th anniversary of the Moon landing on July 20.

As part of the celebrations, a stunning image of the Saturn V rocket that carried Armstrong, Aldrin and Collins into space is being projected onto the Washington Monument this week.

Only 12 men, all Americans, have ever walked on the Moon.

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Be sure to catch the America’s News HQ Apollo 11 50th anniversary special on Fox News on Saturday, July 20 at 12 PM EDT.

Fox News' James Rogers and Matt Leach contributed to this story.

This story is developing...