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The International Space Station flies well within the Earth's magnetic field and the occupants are resupplied with water and food on a regular basis. Also, the length of time any of them are aboard is a maximum of about one year, after which they return to Earth with significant loss of bone density and other effects of sustained zero gravity living. Flying between planets is in another league. The Apollo fights lasted around one week. To Mars and back will, with present technology, take years.

I'm not saying the problems are unsolvable, but it's not really clear how they're going to be solved without a radical jump in technology to maybe, for example, supply the power necessary to create an electromagnetic field around the spacecraft that performs the same function as our planet's. Or develop a water and food recycling system that will sustain the crew. Drinking and eating what used to be urine and feces, without Earth's gradual recycling through soil and sun that allows us to not have to think about it, is something the astronauts might have to learn to stomach. Bottom line, getting the astronauts there is one thing. Getting them there and back alive is something else.

Stay tuned... Musk is going to reveal some of his ideas tomorrow at a conference in Guadalajara.

http://www.theverge.com/2016/9/21/12891322/elon-musk-spacex-mars-colonization-mission-rocket