A step-by-step guide to Elon Musk's vision for interplanetary travel

It's no secret that Elon Musk wants to save humanity.
For years the tech billionaire and founder of SpaceX has said that he wants to make sure the human race is safe from an extinction-level event (like an asteroid strike) on Earth by establishing a city on Mars. But until this week, details about just how he plans to that were scant. 
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On Tuesday, however, that changed when Musk presented his vision for a future society o