President Trump has formally told NASA to send U.S. astronauts back to the moon.
"The directive I'm signing today will refocus America's space program on human exploration and discovery," he said.
Standing at the president's side as he signed "Space Policy Directive 1" on Monday was Apollo 17 astronaut Harrison Schmitt, one of the last two humans to ever walk on the moon, in a mission that took place 45 years ago this week.
Since that time, no human has ventured out beyond low-Earth orbit. NASA doesn't even have its own space vehicle, having retired the space shuttles in 2011. Americans currently ride up to the International Space Station in Russian capsules, though private space taxis are expected to start ferrying them up as soon as next year.
For now, the ultimate goal for human exploration in space remains Mars.
"This time, we will not only plant our flag and leave our footprint, we will establish a foundation for an eventual mission to Mars and, perhaps someday, to many worlds beyond," Trump said.
Exactly how to get to Mars, however, is subject to debate within the space community.
Many see the moon as the best stepping stone, including Rep. Jim Bridenstine, R-Okla., who is Trump's pick to head NASA.
The general moon-first approach being taken by the Trump administration was clearly articulated by Vice President Pence at a meeting of the National Space Council in October.
That's why John Logsdon, a space historian at The George Washington University, says Monday's announcement is not a surprise. "Now the question is whether the White House will propose and the Congress appropriate the funds needed to turn the words into reality," Logsdon says.
Indeed, actually getting the funding to achieve presidents' ambitious space goals is a perennial problem for NASA.
Returning astronauts to the moon had been the plan under President George W. Bush, who called for building a moon base and establishing an extended human presence there. But when a blue-ribbon committee reviewed human spaceflight in 2009, it said there was a mismatch between the scope of the program and the money available to support it: that exploring beyond low-Earth orbit wasn't going to be viable without billions of dollars more in funding.