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.

Don't waste your time on beaming people up or down. Instead, consider gravity waves as advanced physics of the universe that could be used to travel interstellar distances.

When we get there, if we don't find any life on Mars, from that point on there will be life on Mars because we'll bring it there, whether it's germs and leftover urine bags, whatever it is.

Standing on the Moon looking back at Earth - this lovely place you just came from - you see all the colours, and you know what they represent. Having left the water planet, with all that water brings to Earth in terms of colour and abudance life, the absence of water and atmosphere on the desolate surface of the Moon gives rise to a stark contrast.

A space program that truly goes somewhere! With his deeds, not only words, President Obama has revitalized our struggling space program.

There's a historical milestone in the fact that our Apollo 11 landing on the moon took place a mere 66 years after the Wright Brothers' first flight.

Like actors and writers who are on and off again in terms of employment, I had a very unstructured life.