The SpaceX founder’s lifelong dream of Mars exploration has obstacles to overcome. Lots of them.

Humans have placed robots on the surface of the red planet and flown satellites around it, providing high-resolution analysis of its surface and a sense of its geology. But it’ll take more than a decent map to find our way. Despite the phenomenal resources and record Musk brings to the enterprise, there remain a few planet-size holes in his plan.

In short, a lot of things need to be invented before mankind can even make it to Mars—never mind establish a colony.

The most basic component of the complicated mission is the one Musk is in the best position to provide: a heavy-lift rocket. The billionaire’s vision calls for a vehicle capable of launching more than 100 people at a time. SpaceX’s utterly massive Interplanetary Transport System (ITS), unveiled in concept earlier this week, would measure 400 feet nose-to-tail when fully loaded and be powered by 42 of the company’s newly tested Raptor engines.

Read more at Bloomberg