SpaceX CEO and founder Elon Musk tweeted Sunday that SpaceX is accelerating the development of Starship, a rocket that is designed to go to Mars.

He also said that people can start reserving places to Mars after it returns from orbit around Earth.

Musk previously said that Starship has a 60% chance of launching into orbit by 2020.

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SpaceX CEO and founder Elon Musk tweeted Sunday that people can start reserving seats to Mars as soon as Starship, the next big rocket that SpaceX is building, returns from its first orbit around Earth.

Musk tweeted that the development of Starship is being accelerated to build the "Martian Technocracy." When another user asked if people can start reserving places, Musk said, "After Starship returns from orbit."

Starship is a multibillion-dollar, 180-foot-tall rocket that SpaceX says could one day take people to the moon and Mars, as well as launch satellites into orbit. It's part of SpaceX's fully reusable Big Falcon Rocket system, which includes a booster called "Super Heavy." Currently, SpaceX is testing the concepts and engines behind Starship in south Texas.

Musk previously said that Starship has a 60% chance of launching into orbit by 2020. He said he wants to launch a cargo mission toward Mars by 2022 and a crewed mission there in 2024.

In December, Musk tweeted images of the construction of a prototype spaceship at SpaceX's facility in Boca Chica, Texas.