ALL THESE VISIONS are well and good if we only hope to venture to Mars for limited scientific expeditions. But what about the next step; the next giant leap for humankind? What if we want to embark on a longer-term colonisation effort?
To achieve this we'll need to start sending more than just a handful of astronauts every couple of years. This will require either lots of trips at each launch window, or the use of a much bigger ship: more like a spaceliner than a runabout.
One concept for a Mars hauler is the Aldrin Cycler, proposed two decades ago by Apollo astronaut Buzz Aldrin. The Cycler takes advantage of Aldrin's discovery that it's possible to put a spaceship – or even something more substantial, such as an asteroid – into an orbit around the Sun that strategically swings past both Mars and the Earth on a regular basis, keeping on course via carefully adjusted gravity slingshots around each planet. The result is a ship that can be as big as you like because it requires virtually no fuel and never has to land. Instead, crews rendezvous or descend from the Cycler each time it passes one of the planets.
One fly in the ointment is that the best Cycler orbits for outbound trips zip past Mars fast enough to make it hard for shuttles carrying home-bound astronauts to chase them down. (Mars-bound astronauts can simply jump off and use the Martian atmosphere for braking.) Also, the Cycler's return journey may take considerably longer than its outbound one. The solution may be two (or more) Cyclers – one for the trip out, and another, on a different orbit, for the return journey.
The Cycler can also be extended over the course of time as depleted boosters or other components are added to it, making it ever larger and more luxurious. It could be spun for gravity, provided with good radiation shielding, and stocked with the latest in entertainment for the long journey ahead.
Meanwhile, Mars bases would continue to expand. And so too would their demand for resources. Yet this is one of the things that makes Mars such an attractive destination for manned missions. As Zubrin puts it, "precisely the same features that make Mars interesting can make it attainable". This is because Mars has abundant natural resources just waiting for an enterprising colony to tap into them.
For example, water comes from ice melted out of the subsoil or 'regolith'. With solar or nuclear power, the water can be broken into hydrogen and oxygen. More complex chemicals, including rover fuel, come from those plus the atmosphere's carbon dioxide and nitrogen.
Meanwhile, McKay says, it would be nice to find out if we can grow plants in Martian soil. That might be easy, or it might be difficult if the soil proves too salty or otherwise toxic. Recent studies led by Sushil Atreya, at the University of Michigan in Ann Arbor, and Gregory Delory, at the University of California, Berkeley, have found that static electricity from Martian dust devils might be generating hydrogen peroxide snow from the atmosphere that accumulates in the soil at bleach-like levels. If this is the case, it may be necessary to purge toxins from the soil before attempting to grow anything.
What won't be needed is a totally closed ecology, like that tried in the early 1990s in a project called Biosphere 2 (Earth itself was considered to be Biosphere 1). That project, carried out near Tucson, Arizona, involved an attempt by eight 'bionauts' to live for two whole years in a 1.3 hectare sealed habitat, like a giant terrarium. They survived, but their habitat's ecology teetered, hunger reigned, and the experience wasn't exactly what you'd want on an alien planet where you couldn't escape simply by opening the doors and walking home.
The bionauts saw themselves as practising for space. But it wasn't a realistic experiment, says Robinson. True Mars colonies would undoubtedly make heavy use of recycling, but they wouldn't have to recycle everything. "You would do the best you could, then supplement as needed," he says. In fact, that's the whole point of looking for water and finding out how to make useful chemicals from the Martian atmosphere. Still, greenhouses will obviously play a role, even if just for farming. "I think they'd get into the grooviest little greenhouse lives you can imagine," Robinson says.
But there's still one major problem: the Martian surface is a dangerous place, not just because you might asphyxiate if your habitat blew a seal, but because the atmosphere is too thin to block the lethal bombardment of cosmic radiation. Unfortunately, Robinson says, the cancer risk from radiation coming through the thin transparent roof means that you're not going to want to spend a lot of time in that greenhouse. This is not such a problem for the more radiation-resistant plants, but you wouldn't want to idle away too many hours gardening in there without wearing a lead hat.
And there's the rub. Living in one of Zubrin's tuna cans for 18 months might not be any worse than a lifetime of smoking cigarettes. But for permanent colonists? Somebody had better come up with either an easy cure for cancer or some extraordinarily effective – and easily manufactured – radiation shielding. Otherwise, colonists are going to have to live underground – not quite as glamorous as jaunting across Martian hills gazing on red sunsets.
The result is that true long-term colonisation is unlikely in the absence of some kind of terraforming (see "Turning the Red Planet green", p62). Instead, most experts believe the set-up will be more like Antarctica, where scientists go to pursue specific lines of research, revel in the unearthly beauty, and then return home (and have a nice, cleansing hot bath): a once-in-a-lifetime trip they will remember forever, but few would care to repeat. Mixed in with that might be tourists and wealthy retirees willing to accept the radiation danger in exchange for spending their golden years in a truly unique environment.
Still, the dreamers want to go. Some offer utilitarian reasons: each dollar invested will potentially spur many more in technological spin-offs; it's an opportunity for nations to work together peacefully for the benefit of all humankind; if the U.S. and Europe don't do it, the Chinese will; and the more we learn about Mars, the better we'll understand the Earth.
All of these are valid, but ultimately, it's a bit like Edmund Hillary trying to explain Everest: you either get it, or you don't. "It's a symbolic act," says Robinson. "It suggests that a whole civilisation agrees to do something just for the beauty of it. It's like building a cathedral was for the Europeans. It unifies people and gives them a symbol."
It's a symbol that – until we finally go there – will beckon in the night-time sky, like a distant, dusky lantern. It's a symbol that conjures fantasies of dust-red deserts, rock-rimmed craters, and taking the ultimate bushwalk.
Richard A. Lovett is a regular contributor to Cosmos based in the U.S. city of Portland, Oregon.
Read the boxes that go along with this article here in Six things you didn't know about human missions to Mars
