The moment is etched in the collective memory of an entire generation—the blurry black-and-white image of Neil Armstrong descending the stairs of the Apollo 11 lunar module on July 20, 1969 to become the first human being to step foot on the moon. “That’s one small step for man, one giant leap for mankind.”

But this first was not the last for NASA. The United States would go on to complete six crewed missions to the moon that landed a total of 12 astronauts (all men) from 1969 to 1972 in a series of Apollo missions numbering up to Apollo 17. The only mission that failed to reach the moon’s surface was Apollo 13, which suffered a critical power and oxygen failure mid-flight, and was forced to make a heroic emergency reentry.

Rod Pyle, author of First on the Moon: The Apollo 11 50th Anniversary Experience, says that the cultural and technological significance of Apollo 11 can’t be overstated, but that the ensuing Apollo missions also deserve more attention.

For example, Apollo 12, which reached the moon almost exactly four months after Apollo 11, pulled off the space program’s first pinpoint landing. The Apollo 11 lunar module narrowly avoided being smashed to pieces on moon boulders thanks to Armstrong’s last-minute manual adjustments, but the result was an off-target arrival.

Apollo 12 commander Charles “Pete” Conrad and mission control really wanted to nail the second moon landing, which was programmed right next to the Surveyor 3 module, an unmanned NASA landing craft that had been on the moon since 1967.

“And they did it,” says Pyle. “He came right down next to Surveyor 3. It was an astonishing achievement that we don’t hear much about.”

The American public’s initial fascination with landing a man on the moon quickly faded, says Pyle. The Apollo 13 disaster grabbed TV ratings, because American astronauts’ lives hung in the balance. But by Apollo 14, less than two years after 600 million people watched the first moon landing, the prevailing attitude was, “The moon? Been there, done that.”

“I remember watching Apollo 14 as a kid, and there are these two men struggling up the side of a crater with this little wheeled equipment carrier,” says Pyle. “They’re doing the incredible work of exploration and discovery, and then the networks cut away to soap operas. Suddenly I’m watching ‘General Hospital.’ That’s the way it was through Apollo 17, and yet each of these missions did something increasingly daring and fascinating.”

Among the highlights of the later missions was the debut of the “moon buggy,” the first lunar rover. The lightweight unit folded up under the lunar landing module, ran on electric power and boasted its own onboard navigation system that communicated directly with mission control on Earth. Apollo 15 astronauts drove 17 miles across the lunar surface collecting rocks from different geological formations.

The chief mission of the Apollo program, beyond the astounding achievement of landing men on the moon and bringing them home safely, was to carry out an extensive scientific examination of the Earth’s closest celestial body. The Apollo astronauts brought home hundreds of pounds of moon rock, drilled core samples, measured seismic activity (“moonquakes”), collected atmospheric data of the near-vacuum lunar environment, and measured the precise distance from the Earth to the moon.

Leonard David, author of Moon Rush: The New Space Race, sees the Apollo astronauts’ scientific work as unfinished, but critical to understanding not only the moon’s origins, but also that of our own planet and potential Earth-like exoplanets.

“The moon is a witness plate for a lot of solar system history going back billions of years,” says David.

One of the Apollo 15 astronauts brought home an ancient hunk of anorthosite that was later determined to be 4.5 billion years old. They nicknamed it the “Genesis Rock.”

Apollo 15 signaled the beginning of longer and more extensive scientific inquiry on the moon during Apollo 16 and 17. The Apollo 15 astronauts worked for a total of 18 hours and 37 minutes on the surface compared to just over two hours logged by the crew of Apollo 11. By Apollo 17, the biggest news was the inclusion of the first bona fide scientist in space.

Harrison “Jack” Schmitt earned a PhD in geology before signing up for a NASA recruitment program. Pyle says that Schmitt brought a whole new level of expertise to the rock collecting activities, because he was able to intuitively “see the patterns and stories in the rocks around him.” Schmitt is credited with spotting the tiny orange beads that geologists believe are definitive proof of past volcanic activity on the moon.

NASA had built hardware and had plans for increasingly ambitious missions all the way up to Apollo 20, and there was talk of manned flyby missions to Mars and even Venus. But the political winds shifted as quickly as public interest faded.

The Vietnam War raged on, there were riots on American streets, and Congress couldn’t justify spending even more on a space program that had already cost $30 billion. So the last NASA astronauts lifted off from the moon on December 14, 1972, and they’ve never been back since.

Pyle says that higher-ups in NASA flight control were in fact relieved when the order came to shut down Apollo. They understood perhaps better than anyone how lucky they were that no Apollo crew was lost on the way to or from the moon. (Tragically, the Apollo 1 crew died in a pre-launch fire.) Legendary Mission Control pioneer Christopher Kraft was one of them.

“Kraft knew that this magnificent hardware decades ahead of its time was operating in many cases right at the edge of its capabilities,” says Pyle. “He was really afraid that we would lose a crew out there, which would have been a horrible ending to this brilliant program.”

Instead, Apollo morphed into SKYLAB in the mid-1970s, which set the stage for the International Space Station and the Shuttle program. Every so often, an American president toys with the idea of returning NASA astronauts to the moon. President Donald Trump called for increased NASA funding to send men (and women) back to the moon by 2024. He later argued that NASA should forgo a return trip to the moon and instead focus on Mars.

As part of the Artemis program, NASA plans to launch an unmanned rocket to the moon—with the goal of eventually sending the first woman and first person of color to the moon.