I want to keep on the move, keep stimulated and challenged.

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.

Mars has been flown by, orbited, smacked into, radar examined, and rocketed onto, as well as bounced upon, rolled over, shoveled, drilled into, baked and even blasted. Still to come: Mars being stepped on.

I was saddened to learn of the passing of Leonard Nimoy, a fellow space traveler because he helped make the journey into the final frontier accessible to us all.... Indeed, there are strange new worlds to explore -- to seek out new life and start new civilizations. It is time to boldly go where no man -- or woman -- has gone before. Thanks to Leonard Nimoy and his beloved Mr. Spock, the bar has been set high for us to continue humanity's quest to probe outward in the universe.

The society of life on Mars, or the challenge of making Mars more livable, will have significant benefits on our attempts to modify and change in some ways the environment here on Earth.

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

A hybrid human-robot mission to investigate an asteroid affords a realistic opportunity to demonstrate new technological capabilities for future deep-space travel and to test spacecraft for long-duration spaceflight.