Neil Armstrong's death on Saturday has spurred the usual reminders of how drawn-back our collective ambitions are for space exploration. There are lots of reasons for why we don't have moon-bases, some having to do with lack of ambition or lack of money. I'm increasingly inclined to the view that the problem of space travel is simply intractable, for three main reasons:First and most obvious is the problem of speed and distance. Space is too big, and we travel too slowly, to get anywhere beyond this suburban cul de sac of a solar system, in this already unfashionable arm of the milky way.
The second is lack of gravity. Spending months and even years in zero G is far too tough on the human body. The effects on bone density, muscle mass, and eyesight are big problems, and any plausible interplanetary spaceship needs to find a solution.
Finally, there is the problem of our ecological niche. This is the least-understood of the problems with space travel, but probably the most serious. We don't just need food and oxygen -- things that are easy enough to bring into space. We need, for long-term space travel, an entire ecosystem, from intestinal flora on up.
The upshot is that the human body isn't a sort of computer module, a plug-and-play device that can be severed from its connection to the entire ecology of planet earth and sent on its way to the stars. Any possibility for human space travel will require, I think, that we find some way of bringing earth with us. That is, any reasonable space ship will allow us to survive over millennia, and provide us with a sustainable ecosystem that we carry with us. It will also have to have some sort of gravitational field generator that will exert something close to 1-G of pull on our crappy little monkey spines.
Which is just another way of pointing out that we are already traveling through space, on the only plausible spaceship we can imagine. It's called Earth, and it is carrying us slowing through the cosmos, to wherever and whenever, only heaven knows.