Mars is the planet most like Earth in our Solar System. Aside from its lack of air and generally chilly temperatures, it isn’t too unfriendly a place for life. In fact, it may even have had life of its own three to four billion years ago, when it was a warmer and wetter place. It’s also not too far away—the second nearest planet, after Venus—coming to within 55 million kilometers of Earth on occasions.
For these reasons and more, Mars is the most logical place, after and possibly including the Moon, to build a permanently-occupied base. Back in the 1960s, amid the excitement of Apollo, Mars seemed like a natural next step and there was talk of humans landing there within another decade. Since then the public and political will to push on with manned space exploration beyond low-Earth orbit has dwindled. Yet Mars still beckons and it may be that commercial space vehicles will be the first to ferry people there and help establish a permanent outpost.
Getting to the Red Planet, however, is a vast step beyond the Moon. On average, it’s about a hundred times further away, so that the journey time, instead of a mere three days to the Moon in the case of Apollo, would be more like eight months at a minimum, depending on the trajectory chosen to get there. Allowing for some time on the surface for establishing a beach-head to be used by future missions, the whole return trip could hardly occupy less than about a year a half.
Setting aside the technical problems of getting a crewed, and therefore large, spacecraft to Mars and back safely, the physiological and psychological human factors involved are formidable. No one has travelled that far from home, for so long, in such close confinement, without any possibility of rescue if something goes wrong, so there will be uncertainties about the mental well-being of the crew. More worryingly, long-duration stays aboard space stations have revealed serious consequences of many months spent in microgravity, including bone demineralization loss of muscle mass, and cardiovascular deconditioning. Added to these is the risk of radiation exposure if a large solar flare occurs en route. A shielded radiation shelter and, possibly, a rotating section of the spacecraft to generate artificial gravity, may be essential requirements to ensure the health and survival of the crew. All of which will add greatly to the mass of the habitable part of the spacecraft and therefore of propulsion demands.
NASA has no firm plans for a crewed mission to Mars, and would certainly be in no position to attempt one before the 2030s. Other nations, most notably China, may arrive there first. But the most likely scenario at present is that humans will begin to establish a presence on the fourth planet from the Sun courtesy of private enterprise. SpaceX founder Elon Musk has already expressed his desire to retire on Mars and to ferry others there, at $500,000 per ticket, using a massive fully-reusable launch vehicle. The key to ultimate success of a Mars colony will be self-sufficiency, using local materials and resources, and a regular affordable transit system between the two planets.