Sarevok wrote:
It's quite the opposite. Asteroids are cheaper and provide experience before taking on uber projects like Mars.
You're ignoring some key things with your asteroids are cheaper evaluation. For instance you have to spin something BIG to avoid nausea being a huge issue for your colonists. (Its a matter of the spin being slow enough, which requires something huge to provide enough gravity.)
Another gaping issue with a long term asteroid colony is the threat from radiation. On Mars you already have an atmosphere and could very well send out genetically engineered algae along with a couple other measures to work on thickening the atmosphere a bit more to block more radiation prior to humans actually landing on the new colony base. (The point is we could probably send out the genetically engineered algae pretty soon if we wanted to, while we figure out other details involved with actually having a base on Mars and work on establishing the necessary infrastructure for human in advance. If necessary, you could also potentially drill fairly deep into Mars to provide more radiation protection with only the "gardens" where the plants are grown needing to be on the surface.)
The other important difference, at least given what we appear to have learned about the soil so far, is the Mars soil is in fact highly suitable to growing a variety of plants. (I've learned crops that grow in alkaline soil also include Kale, Cabbage, Broccoli, Cauliflower, Collard Greens, Watercress, and Tatsoi among others.) This means you're going to have to mostly bring along nitrates for the crops, while you already have a huge amount of soil and water readily available on Mars. By contrast you're definitely going to have to bring along all your soil for growing crops to your asteroid colony, and water is also going to be a complicating factor you're going to have to at a minimum find. Another related issue is on an asteroid colony providing light for your plants without dangerously exposing your colony to radiation or breaches caused by space debris due to "gardens" being right next to the outside of the asteroid with a transparent bubble for protection is another complication. (You can solve this by having large numbers of powerful lights provide what the plants need, but a large amount of energy will need to be dedicated to this specific task, and you're also going to have to bring up all those lights to the asteroid colony in the first place.)
Another basic point to consider is due to the thread of radiation its going to be easier to have robots do the actual mining of assorted asteroids rather than arranging for building a sufficient radiation protection system and elements of a life support system among other things with each one. Of course if robots are pretty much doing all the actual mining that brings up the question of whether its actually necessary to have humans in an asteroid colony in the first place for asteroid mining in this solar system.