If the human settlement of space is to be made a reality, then the plans for it need to be more measured and realistic.<p>First, it needs to be recognized that we don't know how human biology is going to cope with the radiation and gravity environment encountered in space. More precisely, we know that our biology copes poorly, and we don't know how to fix that from a biological perspective. The only solutions we have in our grasp are one, bring the gravity up to 1G with a rotating habitat, and two, shield humans from the radiation experienced in space with magnets and mass. Any reasonable plan to "settle" space must <i>begin</i> by addressing these.<p>Second, Mars is just not the place to start, because it's too far away. People are fond of pointing out that Mars's atmosphere makes landing there less costly than landing on the Moon, but this ignores the fact that you have to bring life support and food along for the 4- to 6-month long trip. (The atmosphere is also very little help, for example, for Musk's plan.) It is more accurate to say that it is slightly less costly to land on Mars <i>for a day</i> than it is to <i>land an entire Lunar base and live on the Moon for 6 months.</i> Add to this the return trip time to Earth for emergencies (or the time it takes to send emergency supplies and crew), and the Moon wins, hands down. (Indeed, a better place to work out how to survive on Mars would be if you could find places on the Moon where we couldn't land and had to rely on weeks of overland travel from a landing site to get there.)<p>Third, the absolute first step should be an experimental, shielded, rotating habitat (probably built from Lunar materials) in orbit either outside of Earth's van Allen belts or around the Moon. This habitat should be of sufficient size to address the effects of, at least, Moon-like (1/6) and Mars-like (1/3) gravity on human subjects for multiple years. It needs to either be able to spin up and down to these values, have separate sections for Mars and Moon gravity, or we need to have a separate base on the Moon. We already know that space kills us in many, many ways. Until we have characterized <i>how we're even going to survive</i> there, there is absolutely no sense in talking about <i>settling</i> there.<p>Any announcement that doesn't address these directly is just PR.