A sunrise view of the Artemis I Space Launch System (SLS) and Orion spacecraft at Launch Pad 39B at NASA’s Kennedy Space Center in Florida.
NASA—Ben Smegelsky
July 22, 2022 4:04 PM EDT

You could go your entire life without thinking about a collet. Indeed, you could go your entire life without even knowing what a collet is, and if we stopped right here you’d be no worse off. For the record, though, a collet is a small ring of metal, about the size of a fist, and, as NASA announced at a July 20 press conference, at the moment, it’s the biggest thing standing in the way of the U.S. having humans back on the surface of the moon sometime in the middle of this decade.

The collet in question is attached to the hydrogen fuel line of the main stage of NASA’s new mega-moon rocket, the Space Launch System (SLS), a 97 m (318 ft) beast of a machine, capable of producing 4 million kg (8.8 million lbs) of thrust. NASA hopes to launch the SLS on an uncrewed shakedown cruise around the moon and back, a mission known as Artemis 1, sometime in late August or early September—a flight that would be followed by an identical crewed mission in 2024.

But before Artemis 1 can fly, NASA had to go through a so-called wet dress rehearsal, during which the rocket would be rolled out to the launch pad, loaded with 2.8 million liters (740,000 gal) of liquid hydrogen and oxygen fuel and run through a simulated countdown. Four times NASA attempted the wet dress rehearsal and three of those times it failed for one technical glitch or another.

At last, in late June it largely succeeded, with the only problem being the cursed collet, which turned out to be loose. During a real launch that would have prevented the hydrogen fuel line from separating from the rocket properly. So now, the SLS is back in its hangar, with engineers working on that final problem—and confident they can fix it.

If they can, the moon mission is on—marking the first time the U.S. will have sent a crew-rated (but not actually crewed) spacecraft on a lunar journey since Apollo 17 in December 1972. The exact timing of the mission depends on the relative positions of the Earth and the moon, and means that there are three dates on which Artemis 1 could launch in the immediate future: Aug. 29, Sept. 2, and Sept. 9. If the space agency misses those launch windows, the mission would slip to late September or early October.

The profile of the mission, which will last about 40 days, involves the SLS flying an Orion crew vehicle first into Earth orbit and then on a long looping trajectory that will see it fly around the moon at altitudes ranging from just 100 km (62 mi.) to 70,000 km (43,000 mi.). The Orion capsule will then return to Earth, slamming into the atmosphere at about 32,000 km/hr (20,000 mph) and sustaining temperatures of up to 2,700ºC (nearly 5,000ºF) on its heat shield, before splashing down in the Pacific off the San Diego coast.

When the Orion capsule is pulled from the water, there will be nobody inside to greet and congratulate. But the next time the SLS flies, four astronauts will be aboard. Nearly half a century ago, the U.S. abandoned the moon. In as little as six weeks, we could begin to reclaim it.

This story originally appeared in TIME Space, our weekly newsletter covering all things space. You can sign up here.

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Write to Jeffrey Kluger at jeffrey.kluger@time.com.

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