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

I've been to the Titanic in a yellow submarine and the North Pole in a Russian nuclear ice breaker.

Exploring Mars is a far different venture from Apollo expeditions to the moon; it necessitates leaving our home planet on lengthy missions with a constrained return capability.

I expected the unexpected and went [on the Moon] with an open mind. I think the visual scene was described by my words on first landing - "magnificent desolation." Magnificent for the achievement of being there, and desolate for the eons of lifelessness.

My Sunday mornings are spent in a recovery meeting in Pacific Palisades.

Mars is the symbolic and totally stimulating next objective that could so dominate the next century's exploration efforts. From Mars, the resources of all the asteroids will become readily available.

There are always door openings. And gradually, it accumulates. The opportunities open up in front of you.