Robert Walker, a self described inventor and programmer, recently published a piece in Science 2.0 presenting the case for not colonizing Mars. His position will surely draw some dissent, especially from Mars settlement activists.
Walker’s objections to Mars colonies include environmental reasons (too cold, too much radiation, low gravity, too much dust, and so on) as well as technical reasons (hard to get spare parts, for example, though he seems to discount the immediate promise of nanotechnology and 3D printing.)
The case against Mars is certainly debatable, but Walker believes that he has a solution. Build an colony orbiting Mars and explore and develop the place by tele-operated robots. While Walker may not go as far as using the robots to prepare for a Mars colony, it is an idea worth considering. The concept is similar to one devised by Paul Spudis and Tony Lavoie to use robots to build a lunar base, prospecting for resources, in advance of a human return to the moon.
In the expansion of Walker’s idea, the tele-operated robots would not just explore here, but would gather resources and build infrastructure to prepare the way for humans. They could even start the long process of terraforming the Red Planet, recreating what Mars is thought to have been billions of years ago, green, lush, with surface water and a thick atmosphere.
On terraforming, while most scenarios for terraforming Mars involved thousands of years with known technology, though advances in nanotechnology and genetically engineered flora could advance that time. One rather radical idea would be to simply bombard Mars with water and ammonia rich asteroids which would create greenhouse gasses and flood ancient sea and river beds with water, bringing a temperate climate to Mars within just 50 years. That would delay human habitation of Mars, except for relatively brief visits, but the Mars that would be settled around 2100 would be like a second Earth.