Sending a couple of guys to the Moon and bringing them back safely? That's a stunt! That's not historic.

There's a tremendously satisfying freedom associated with weightlessness. It's challenging in the absence of traction or leverage, and it requires thoughtful readjustment. I found the experience of weightlessness to be one of the most fun and enjoyable, challenging and rewarding, experiences of spaceflight. Returning to Earth brings with it a great sense of heaviness, and a need for careful movement. In some ways it's not too different from returning from a rocking ocean ship.

I think both the space shuttle program and the International Space Station program have not really lived up to their expectations.

Sending a couple of guys to the Moon and bringing them back safely? That's a stunt! That's not historic.

Computers allow us to squeeze the most out of everything, whether it's Google looking up things, so I guess that tends to make us a little lazy about reading books and doing things the hard way to understand how those things work.

Going to Mars would evolve humankind into a two-planet species.

Every couple of years, we could dispatch people from Earth to Mars.