If they are free to walk out at any time, why is the capsule locked? (No, seriously.) The other thing that jumps out at me is the duration of the trips but the relatively short amount of time (two days) spent on 'Mars'. Surely a mission to Mars would include more time on the planet? The time spent on the planet would be more intellectually stimulating than the spaceflight (one presumes) and might offer relief/reward from the journey to Mars and better prepare the crew psychologically for the return mission. I wonder why that wasn't factored in. The difficulty of simulating the on-planet experience perhaps?
Bonus question: Would an actual mission to Mars pay astronauts more than $70,000 per year?