SpaceX chief executive Elon Musk on Tuesday outlined an ambition to send humans to Mars with methane-fueled reusable spaceships and the largest rocket ever built, an effort he said will likely require government support and initially cost billions of dollars to develop and test.

Musk’s rollout of his Mars colonization vision, a glitzy reveal years in the making, included a description of an architecture that could eventually ferry more than 100 people to the red planet on each expedition, and perhaps thousands if SpaceX and its partners could muster support to build a fleet of boosters and airliner-sized spaceships.

“What I want to do is make Mars seem possible, to make it seem as if it’s something we can do in our lifetimes, and that you can go,” Musk said.

SpaceX plans to launch its first mission to Mars, a robotic test flight with a modified Dragon capsule, as soon as May 2018. After that “Red Dragon” flight, Musk said SpaceX’s goal is to send at least one spacecraft to Mars during every interplanetary launch opportunity, which come every 26 months or so