"My vision is for a fully reusable rocket transport system between Earth and Mars that is able to re-fuel on Mars - this is very important - so you don’t have to carry the return fuel when you go there. The whole system [must be] reusable - nothing is thrown away. That’s very important because then you’re just down to the cost of the propellant. We will probably unveil the overall strategy later this year in a little more detail, but I’m quite confident that it could work and that ultimately we could offer a round trip to Mars that the average person could afford - let’s say the average person after they’ve made some savings."