But the question is, do I agree with it when it's 1-in-100, when it's 1-in-50, if it's 1-in-20. That is a policy question. At what probability do you begin to spend hundreds of millions or billions of dollars in order to do something?

We're sitting in a shooting gallery, with hundreds of thousands of these things whizzing around in the inner solar system. So it's just a matter of time.

We were at one point.

The frontier in space, embodied in the space colony, is one in which the interactions between humans and their environment is so much more sensitive and interactive and less tolerant of irresponsibility than it is on the whole surface of the Earth.

It would take an extremely large spacecraft to deflect a large asteroid that would be headed directly for the Earth.

As a former Apollo astronaut, I think it's safe to say that SpaceX and the other commercial developers embody the 21st century version of the Apollo frontier spirit.