In 2018, Musk said, an unmanned Falcon Heavy rocket will fly to Mars carrying a Dragon capsule—a version of the vehicle SpaceX has delivered to the International Space Station. The flight would be primarily intended to test and gather data about the trip, though it will also carry experiments.

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Starting in 2020, SpaceX hopes to launch multiple Falcon Heavy rockets during each biannual launch window, again packed with experiments from third parties—presumably an important element in at least partially funding the missions.

“It’s a regular cargo route. You can count on it,” Musk told the Post. “It’s going to happen every 26 months. Like a train leaving the station.”

In 2022, the Mars Train will include the Mars Colonial Transporter, or MCT, a rocket carrying the first key infrastructure for a permanent city on Mars. The rocket will be even bigger than the Falcon Heavy, with lift capability of about 100 tons to Falcon Heavy’s 54. A version of that rocket has been referred to by SpaceX developers as the Falcon XX.

What’s remarkable about this timeline is that even the Falcon Heavy will not be tested until later this year. The Raptor engine designed for the even-bigger Mars Colonial Transporter rocket has been under development for years, but there is still very little concrete information, even as Musk says it will fly by 2022.

For more on SpaceX and Mars, watch our video:

The following launch, in 2024, would carry humans. Musk emphasized to the Post that the timeline requires that SpaceX “get lucky and things go according to plan,” and that the first human mission would entail “great risk” for those on board.

“It’s dangerous and probably people will die—and they’ll know that,” said Musk, emphasizing that early Mars explorers will be willing to face risk, in exchange for being part of a bold new chapter in human history.