I agree with Sam and Hari. Doing an orbital mission to Mars is a waste of 4 years and has risk enough to redo that mission before landing. To significantly reduce risk, it is much better to focus on using the Moon for a landing mission. Treat the Moon as a little 'Mars'. Repeat several times to perfect a landing and a 'first base' mission. Then set out for Mars. The landing can always be changed to orbit only, if problems arise. Adjustments would be made to account for no atmosphere on the Moon and smaller gravity. Mars can be done by 2033 with lower total cost and much less risk - IMO.