There were about six years when there was not one American who went into space. We shouldn't do that again.

There's no guarantee that the United States will be around 200 years from now.

At the core of the risk-free society is a self-indulgent failure of nerve.

If you want poets in space, you'll have to wait.

Exploration is wired into our brains. If we can see the horizon, we want to know what's beyond.

In my mind, public space travel will precede efforts toward exploration -- be it returning to the moon, going to Mars, visiting asteroids, or whatever seems appropriate. We've got millions and millions of people who want to go into space, who are willing to pay. When you figure in the payload potential of customers, everything changes.

One of the major problems with long-term deep space human flight is the requirement for radiation shielding.