This is Part 3 of a four-part series on Elon Musk’s companies. For an explanation of why this series is happening and how Musk is involved, start with Part 1.

Pre-Post Note: I started working on this post ten weeks ago. When I started, I never intended for it to become such an ordeal. But like the Tesla post, I decided as I researched that this was A) a supremely important topic that will only become more important in the years to come, and B) something most people don’t know nearly enough about. My weeks of research and discussions with Musk and others built me an in-depth, tree-trunk understanding of what’s happening in what I’m calling The Story of Humans and Space—one that has totally reframed my mental picture of the future (yet again). And as I planned out what to include in the post, I wanted to make sure every Wait But Why reader ended up with the same foundation moving forward—because with everything that’s coming, we’re gonna need it. So like the Tesla post, this post became a full situation. Even the progress updates leading up to its publication became a full situation.

Thanks for your patience. I know you’d prefer this not to be a site that updates every two months, and I would too. The Tesla and SpaceX posts were special cases, and you can expect a return to more normal-length WBW posts now that they’re done.

About the post itself: There are three main parts. Part 1 provides the context and background, Part 2 explores the “Why” part of colonizing Mars, and Part 3 digs into the “How.” To make reading this post as accessible as possible, it’s broken into five pages, each about the length of a normal WBW post, and you can jump to any part of the post easily by clicking the links in the Table of Contents below.