I know Elon, we're very like minded in many ways. We're not conceptual twins. One thing I want us to do is go to Mars, but for me it's one thing. He's singularly focused on that. I think motivation wise, for me I don't find that Plan B idea motivating. I don't want a plan B for Earth, I want Plan B to make sure Plan A works.

Your probability of dying on Mars is much higher than earth. Really, the ad for going to Mars would be like Shackleton's ad for going to the Antarctic: "It's gonna be hard. There's a good chance of death, going in a little can through deep space. You might land successfully. Once you land successfully, you'll be working nonstop to build the base."

Land on Mars, a round-trip ticket - half a million dollars. It can be done.

The revolutionary breakthrough will come with rockets that are fully and rapidly reusable. We will never conquer Mars unless we do that. It'll be too expensive. The American colonies would never have been pioneered if the ships that crossed the ocean hadn't been reusable.

If humanity doesn't land on Mars in my lifetime, I would be very disappointed.

We're working to lower the cost of spaceflight so that many people can afford to go and so that we humans can better continue exploring the solar system. Accomplishing this mission will take time, and we're working on it methodically.