Soon the day will come. The technology is making the mission more cost efficient. The plan is to have the mission last for 18 months. Gravity Gravity is a major problem facing the mars mission. The zero gravity of space can make muscles deteriorate slowly, and that will make them useless.
Exercise is very important to help prevent that.
Treadmills will probably be the main piece of exercise equipment on board, a vacuum will imitate gravity so the person exercising will get the whole benefit. They would have to exercise two times a day. This will also help to coop with boredom. Food Food is another problem since we can't take enough food to last 18 months. The mass would be too tremendous.