Unless we are able to commit to a permanent growing settlement [on Mars], then I don't think just going there with humans and coming back is worth doing. The expense of planning to come back is like the people who left Europe to come to America and then to turn around and go back to Europe, it really doesn't make any sense at all.

The first human beings to land on Mars should not come back to Earth. They should be the beginning of a build-up of a colony/settlement, I call it a 'permanence'.

As we begin to have landings on the moon, we can alternate those with vertical launch of similar crew modules on similar launch vehicles for vertical-launch tourism in space, if you want to call it that adventure travel.

Dwelling on an engine failure for a pilot as he rolls down the runway is NOT what he should be thinking about - it's obtaining a smooth liftoff! But in the back of his mind, he knows exactly what to do (or pretty much) and in many cases, if he's alone in the fighter aircraft, he has to leave that aircraft in an ejection seat in a big hurry!

I'm in favor of changing the destination of humans. There are a lot of manned missions that can be done, but not in the direction of the moon.

To send humans back to the moon would not be advancing. It would be more than 50 years after the first moon landing when we got there, and we'd probably be welcomed by the Chinese. But we should return to the moon without astronauts and build, with robots, an international lunar base, so that we know how to build a base on Mars robotically.

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.