The United States is , and took a monumental step towards that giant leap back into space by rolling out the Artemis I rocket to the launch pad Tuesday night. To get there, it took a ride on the back of one of NASA’s Crawler-Transporters — the largest vehicles on Earth.

The four-mile trip from Kennedy’s Vehicle Assembly Building to Launch Complex 39 started Tuesday night and took 12 hours to complete, finally ending at a launch pad at the Kennedy Space Center on Merritt Island, Florida 12 hours later Wednesday morning. NASA set a launch window for August 29, with backup dates in early September. This first phase of the Artemis mission is an unmanned fly by of the moon, complete with the , which will eventually carry astronauts for a manned fly-by of the moon in 2024. Artemis III will see American boots — or really, any boots — on the lunar surface for the first time since 1972. A moon basecamp is the goal of these missions.

At 131 feet long and 114 feet wide the crawler-transporters are undeniably large, but with a top speed of one mile an hour loaded (and a blistering two miles an hour unloaded) they are definitely cumbersome giants. Burning a gallon of fuel for every 32 feet traveled, the Crawler-Transporters might also be some of the least efficient vehicles ever, require a 5,000-gallon tank to get going. Despite the ponderous speed limit and thirsty 16 diesel-electric locomotive engines, Crawler-Transporters have traveled 5,000 miles in their 50 years of service.

The Crawler-Transporters have been a part of NASA’s space exploration mission since 1965, when the behemoths moved Saturn V rockets around Cape Canaveral. A platform the size of a baseball diamond sit atop the crawler, which is capable of moving 18 million pounds of weight. Even that incredible load isn’t enough for Artemis however. This Crawler had to be reinforced to carry the even heavier rocket-launch tower combo you see in the video.

The U.S. to the lunar surface. China’s will launch in 2024 and as a possible spot for an international moon base.

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