On the subject of cheesiness... Life is what you make it, and simulated Mars missions are no exception. It's possible on the one hand to treat this whole exercise as a joke -- grown men and women dressing up and playacting. On the other extreme, some participants have been known to get really, really serious about the simulation, making unnecessary problems for themselves and others. But there's a middle road where common sense prevails, where hard work and serious intentions combine with a playful sense of discovery.

To make an imperfect analogy, flight simulators are not "fake flying." They're not real flying either, and as such they're neither pointless nor joyless. What they are is a training tool, which millions of people have used to familiarize themselves with the mechanics of flight. Microsoft Flight Simulator won't make a pilot out of you, but if you try it out and (a) don't like it, or (b) can't handle it, then this is a clue that you're not really cut out to be a pilot. Conversely, if you master the sim and find its little details thrilling rather than tedious, then you probably do have the Right Stuff, and can expect a better-than-average time at a real flight school somewhere.

So. The way I saw it, this expedition was not so much a fake Mars mission as a genuine training exercise. Most of us there at the hab would probably never go to Mars for real, but that didn't make the training any less valid. Like many of the "useless" classes we took in school, the experience helps shape our viewpoint and our understanding of the wider universe. It enriches us as people. After just four days in this desert, I'd added dozens of useful skills to my self-reliance tool kit, and we hadn't even started the sim!

Our commander, Alejandro Diaz, is a Boeing engineer who works closely with the astronauts on the Space Shuttle and Space Station programs. And following his lead, we were shaping up to be a cautious and methodical crew. On day 4 there was still no full-dress "extravehicular activity," or EVA. Instead, we worked our way toward it with a sort of "practice sim" or "simulated sim," where we went out without space suits. There's nothing cheesy about this, either; real astronauts don't go to space until they've rehearsed their mission in water tanks, and they don't enter the tanks until they've walked through the steps in a dry mockup, and they don't even do that until they've been thoroughly trained and briefed on the missions equipment and objectives.

Step by step, we inched our way toward realism, starting with a test of the base's long-range radio repeaters - which weren't working and would clearly need to be serviced. We also mucked around with battery chargers and microphone headsets, and cleaned things up in the GreenHab, which is connected to the habitat structure and processes our wastewater through trickling filters and 5 different baths of algae and bacteria.

Later on in the afternoon, we did several hours of navigation exercises with maps, compasses, and GPS. Arguably, the compass is not a realistic piece of simulation hardware, since Mars doesn't have a planetary magnetic field like Earth's. However, there are several strong regional fields generated by magnetic materials in the planet's crust, and any future Mars astronauts would be silly not to use them as nav aids. Believe it or not, the GPS is realistic, since the Mars Global Surveyor and several other satellites in orbit around the planet have been equipped with GPS-like clocks and radio transmitters. Accuracy is not great right now, but as more and more spacecraft arrive at the planet, the system can only improve. By the time we start landing astronauts there, they should have little trouble finding their way.

Anyway, by some strange coincidence three members of our six-person crew were born in New Jersey and now live in Colorado. PhD aerospace engineering student Jim Russell and jack-of-many-trades Bill Foltyn are both hardcore backpackers, and as a Colorado near-native and former boy scout I've spent a bit of time in the wilderness myself. Alex Diaz, who moved from Peru to Los Angeles at the age of 10, had limited hiking experience, and our British colleagues had none at all. But with a few hours of training and appropriate team assignments, there was little doubt they'd do well.

The exercise was another practice EVA: a two-hour hike, sans spacesuits, where we deliberately got ourselves mildly lost and asked the trainees to navigate us back to the hab. Not only was the exercise successful, but it took us through some of the most striking terrain I've ever seen. Not all of it looks exactly like Mars, but it all certainly appears to be an alien world of some sort. We made several weird discoveries along the way; natural caves and odd spiral-shaped imprints in the rock. The hills are covered in rubble on their northern faces, while on the south they're just stripey mounds of bare dirt. We did a lot of speculation about this, and Bill (our geologist, among other things) was in hog heaven, dashing from rock to rock in great excitement, or else plopping himself down on the ground to stare at one spot for minutes at a time.

In an environment like this, it's hard not to be a scientist. Why does it look like that? How did it get that way? Obviously, this area had been studied by geologists before and is probably well understood. We're not really adding to the sum total of human knowledge. But we're learning the art of exploration, and more importantly, the art of making that exploration meaningful.