Scientists are aware of the problems and danger of going on a long trip to Mars and what it can do to the human body. The most concern problems in the space travel are exposure to the solar radiation, bone loss, and muscle loss.  

It will take about 7-9 months to travel to mars and land. Some other problems on the Mars travel will be, technology, a closed life of support system, 1/3 of gravity after micro gravity, communtication lag, psychological issus,(such as boredom,depression,loneliness,etc.) and growing their own food.