"I'm convinced that the first person to step foot on Mars will arrive there riding on a Boeing rocket," said Boeing CEO Dennis Muilenburg in a confident manner. "While in the long run, it doesn't really matter whose logo arrives first, competition will be key to establishing ourselves as a multi-planetary species. It got us to the moon, after all."
With the two companies both more interested in making the craft that will get people there, other scientific quarters are more concerned at how the people will survive in such extreme conditions.
The biggest concern is a study food supply. The journey to Mars will likely take around 24 months. This is a terribly long time, and tube food will not be sufficient. Carrying food, even for one person that would last two years would probably fill the whole craft. The only viable option is by growing the food which by itself is incredibly difficult.
John Phillips stayed on a space station for ten months, and after leaving earth with 20/20 vision came back with 20/100. NASA explained that the gravitational force led to his eyeball changing shape. At the moment the only way to equalize pressure to avoid change of the eyeball shape is by drilling the skull.
Radiation is also an obvious problem they will face. Scientists estimate that the amount of radiation received over the journey alone would accumulate to the same level of radiation you would be exposed to if you were exposed to 24 CAT scans.