Elon Musk is proposing a ton of audacious things to get to Mars before the 2020s are over. But perhaps the most striking feature of his plan is the simplest. He’s not just sending people to Mars; he’s planning on bringing them back.

At this point, every journey to Mars has been a one-way trip. NASA is only just now planning a rover for a 2020 launch that will gather samples for return to Earth—how we’re going to get the small collection of samples back hasn’t yet been specified. By contrast, Musk intends to return everything: the people, the ship, and presumably any souvenirs that clear customs. That intention is going to require radically rethinking the approach.

One of the key things that will have to change is what our hardware does once it gets there. So far, all our equipment has been designed to sample the chemistry that’s present (though that will change on the 2020 rover—we’ll have more on that in an upcoming story). Musk’s plan envisions creating a chemical factory on the red planet, one that makes all the fuel needed to get back off the surface and return a ship to Earth.