I had done everything I could do as an astronaut, and we have a long line of inexperienced astronauts waiting for their first missions, and so my role really should be to step aside and help them prepare for their missions, rather than to try to get another mission.

In a big picture sense, it's more national prestige that we're risking. You know, we are proud of our space program, but as we were talking earlier, the average American doesn't think that much about it right now. So, it may seem like something we could just give up and not really worry about it, but I think it starts creeping into the national psyche. If American astronauts have to hitch rides with the Russians or other nations in the future.

The Americans are still the leaders in human space flight. I feel we have a danger here of kind of stagnating. We're kind of resting on our laurels and there's a danger going forward if we don't take bold steps to really support human space flight in this country that we could fall behind. After the space shuttle is retired, we're going to have a big gap, five to seven years, at least where we're not going to have the ability to send our own astronauts into space, we'll have to buy rides on the Russian Soyuz, and so that will be a pretty big step down for us.

I actually had four space flights altogether, three times on shuttles. My second flight was really unique for me because I was going back into space, first of all. The first one was like an appetizer at a nice dinner. You know, you want to go up and you want more. So, the second time I got into space, it was neat because I got to actually do two space walks.

Space is very unforgiving business

One of the biggest concerns about going out beyond lower Earth orbit is the radiation. We find that exercise seems to counteract a lot of the negative effects of space flight, like bone loss and muscle atrophy and cardiovascular systems issues. We exercise two hours a day on the station, which is a huge hit out of your day. It's great for staying in shape, but you know, it cuts into the productivity of the crew and if you look at how expensive it is to get a crew into space, if we can keep them healthy and have them exercise, but spend less time doing it, we can get more done.

I'm Chinese-American, of course, and so it's very interesting to see China actually launch their own astronauts, becoming the third nation, following the United States and Russia, to do so.