Aeon Magazine has a new essay written by Ross Andersen about Elon Musk, the well-known tech entrepreneur behind companies like Paypal, Tesla Motors and SpaceX. The essay made news this week because in it Musk says that any future human colony on Mars will 'need a million people' in order to be self-sustaining. As Andersen says, 'Musk is a revivalist, for those of us who still buy into cosmic manifest destiny.' But he does have a history of both making bold claims and backing them up. The essay is worth reading in full but here is an extract on how Musk intends to do it: 

Great migrations are often a matter of timing, of waiting for a strait to freeze, a sea to part, or a planet to draw near. The distance between Earth and Mars fluctuates widely as the two worlds whirl around in their orbits. At its furthest, Mars is a thousand times further than the Moon. But every 26 months they align, when the faster moving Earth swings into position between Mars and the Sun. When this alignment occurs where their orbits are tightest, Mars can come within 36 million miles, only 150 times further than the Moon. The next such window is only four years away, too soon to send a crewed ship. But in the mid-2030s, Mars will once again burn bright and orange in our sky, and by then Musk might be ready to send his first flurry of missions, to seed a citylike colony that he expects to be up and running by 2040.

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Musk told me all this could happen within a century. He is rumoured to have a design in mind for this giant spaceship, a concept vehicle he calls the Mars Colonial Transporter. But designing the ship is the easy part. The real challenge will be driving costs down far enough to launch whole fleets of them. Musk has an answer for that, too. He says he is working on a reusable rocket, one that can descend smoothly back to Earth after launch, and be ready to lift off again in an hour.