We have the ability, at such high fidelity, to simulate the physical world through computers. But when the spiritual world or human behavior comes into play, we don't have a very good model for that at all.

We can't start over and develop a Saturn 5-type vehicle from scratch.

I think I need to continue to think and plan and marry all of the different things that we could do that make transportation in space from the earth to the space station, from the earth to the moon to space stations around the moon to visiting an asteroid.

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

NASA needs to focus on the things that are really important and that we do not know how to do. The agency is a pioneering force, and that is where its competitive advantage lies.

The way I see it, what is going to come out of the moon activities is a respect for U.S. leadership.

If you want to say that the sky is black, and if I'm there, even if I fall back down again, I will be weightless for a period of time - maybe that's the definition of space.