Let’s say you’ve picked the perfect spot for building a settlement on Mars. This means that any Martian settlement will have to rely almost entirely on natural resources, something called in-situ resource utilization. So we have to be very clever with what we build, where we build, and how we build. But to really build out a settlement you need to build, which means you need a lot of raw materials. In 2006 a researcher named Bruce Mackenzie with the Mars Foundation developed the Homestead plan, which reasonably approximates the steps a future Mars settlement would have to perform to become self-sustaining, and what they can safely assume and not assume given another few decades of technological development.