Today, Hickam and Simberg debate genetic solutions to the challenges of long-term space travel. Previously they discussed the grudge match between private space entrepreneurs and the federal space agency, examined the moon and Mars for signs of human life and assessed national space ambitions and NASA's role in achieving them.

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So here we are at the end of our Dust-Up, Rand. I've enjoyed our civil and cordial discussion, recognizing that we both want what is best for our country and for the exploration of space.

I'm going to get to today's provocative questions, but first I'd like to reflect a little on some of the commentary we've received during the week. Some of the folks who have written come across to me as essentially pessimistic and reflexively negative, not only about the space program but about life in general. This bothers me, especially because I believe that Americans should always be optimistic, considering who and what we are and the freedoms we have. I have always found the best way to live is to be optimistic and energetic and willing to work hard for my dreams as well as the dreams of others.

Negative attitudes, in contrast, are terribly self-destructive. I wrote a book called "We Are Not Afraid" that maybe could help some of these folks, who I'm sure really don't like being so miserable. I'm not trying to sell a book here — it came out in 2002 and already had a great run — But I do urge folks who think life is a little slice of hell, and nobody is good, and nothing wonderful is ever going to happen to them to maybe go to their local library and take a peek at it. I want all those sour, gloomy folks out there who seem to have trouble grabbing the spark of a good life to rethink the way they think. Remember, it isn't the dreamers who have good lives, it's the doers. Remember also what I call the three Ps of success: passion, planning and perseverance. First, look inward and figure out what your passion in life is. Then, get yourself a plan to attain it, which almost always means more education. Of course, the most important of the Ps is perseverance. Persevere with a plan to reach your passion and life will be good. This I promise. Of course, Rand, you know all this. You have a good productive life because you knew instinctively the three Ps.

Now, to the question of the day. Rand, I doubt seriously that genetic engineering and modifying human beings is ever going to play a role in space exploration. The moral and philosophical ramifications of such an idea are breathtaking to the extreme. And from a practical viewpoint, why bother? We already have robots to explore space, and we can design them even better in the future. Even genetically tweaked flesh and blood is never going to be as strong and durable as steel titanium, and aluminum. Of course, if the world got taken over by some neo-Nazi outfit in the future, I guess anything is possible, but otherwise, it isn't likely to happen.

The second question on whether humans in their present form can survive long trips into deep space is a really good one. The answer is, it depends on the ship, how fast it can go, the destination and the humans going. Because we don't have any starships, nor will we for some time, I'm going to focus on a tangible mission, humans to Mars. This much we know for certain. The space between Earth and Mars is a very harsh place. It has temperature extremes from super-hot to super-cold, and it is filled with deadly radiation.

Mars is also a very, very long way and, using our present technology, i.e. chemical rockets, it would take many months to get there. One thing we've learned about space is that the human body starts to fall apart after relatively short exposures to microgravity (weightlessness). Our bones atrophy, our muscles go soft and our hearts get weaker. Of course, artificial gravity would help that situation, but so far the only idea anyone has come up with is to put space humans in a big centrifuge. The problem with that is no one has ever tried it and we're not sure how the human inner ear will take it. It just may be that if we landed a human on Mars after being spun for some months, he would stagger around like a drunk congressman. Even when his head stopped spinning, likely our poor human would glow in the dark from all the radiation received on the way.

So all this is my way of saying that I sincerely doubt humans are ever going to Mars on chemical rockets. It's just too long a trip for mere mortals, even ones who love to be cooped up for months and don't mind getting cancer, damaged hearts or early osteoporosis.

So what's a Mars ship designer to do? The answer is he must design a ship that gets through space just as fast as possible, one that can zip through all that radiation and maybe provide a little gravity along the way. In other words, what is needed to go to Mars are nuclear ships, big boomers that once lighted, stay lighted to accelerate halfway to Mars, then turn around to decelerate, thus providing a form of straightforward gravity. Nukes could get humans to Mars in a matter of weeks, not months, meaning their human cargo would be in pretty good shape to land and go to work. So you "Let's go to Mars" folks, start pressing for big, bad nuclear rockets if you're really serious. To consider this idea further, you might want to take a look at an interview on big space boomers I gave to Nuclear News a couple of years ago.

So as Forrest Gump said, that's all I've got to say about that. Thank you, dear readers, for sticking with us. I hope we've said some things you haven't considered and will now give some thought. And thank you, Rand, for a most interesting discussion. I hope you've enjoyed it as much as I have!

Homer Hickam is an engineer, former NASA designer and astronaut trainer, a veteran of the 4th Infantry Division in the Vietnam War and the author of nine bestselling books, including the acclaimed memoir "Rocket Boys," which was made into the film "October Sky."

Don't count the mutants out just yet

Well, Homer, I agree with you about the pessimists. I'm fundamentally optimistic about our future, here on Earth and in space, though it sometimes seems as though the folks in Washington are doing everything they can to peg my gloom meter. But I think that you yourself are too pessimistic about what advances we'll be making in biotechnology and other related areas in the future, perhaps even the near future.

I have nothing against nuclear rockets, and am in fact all in favor of them. But I don't think that they're a panacea for the challenges of the extraterrestrial environment to human physiology. Fortunately, people are already working on techniques — some of which derive from existing natural ones that we're born with but which our bodies forget how to do as we age, and some artificial ones that use molecular-level devices for doing body repair at a cellular level. The even better news is that they are doing so for reasons having nothing to do with spaceflight, which means that their continued funding will be more secure.