Over the moon, and how we'll get there

SpaceX "Dragon" vehicle with cargo from Earth berthed at International
Space Station. Photo: NASA
Often when we meet, Harry manages to put in a plug for the colonization of Mars. I used to kick myself for telling him that I was writing another book about the solar system, causing him to assume that I am a Mars fellow traveller. “I can’t imagine why, after our success with Project Apollo, we just didn’t follow it up with a manned mission to Mars,” he says, shaking his head unhappily. “...