"For some time, I thought Apollo 13 was a failure. I was disappointed I didn't get to land on the moo..." — Jim Lovell

Mars is a long ways away. The moon is only 240,000 miles, but Mars is in the millions. It's too risky without spending more time going to the moon.

In space-flight terms, six landings on the moon back in the Sixties and Seventies doesn't mean much.

My view is that we should go back to the moon, build up the infrastructure to make flights there commonplace - be comfortable with it - then use that infrastructure to expand and go to Mars.

I was a naval officer and aviator. I tested airplanes and got selected to be an astronaut later on.