Poynter said the Biosphere 2 crew created music using the sounds from the animals and machinery in the biosphere. Music-making or reading would be options on the Mars journey, too, she said.

Eventually, presumably, Mars would come into view.

"To look down on Mars and be the first people to see, potentially, our future home planet --" Poynter interrupted herself to let out a high-pitched "Oooo!" -- "gives me chills just thinking about it."

... And other health issues

Besides mental factors, gravity differences in space present a slew of physiological challenges that aren't easily simulated on Earth over long periods of time. There's evidence that the visual system can be impaired, and the weakening of bones and muscle may occur, Kring said.

How the two people aboard the space capsule would deal with these sorts of issues, on top of mental stress, remains to be seen -- as does whether the mission will actually launch as envisioned in January 2018.

"I'm all for supporting this, and I certainly am a big proponent of human spaceflight, but I wonder if all of this can be figured out in five years," Kring said.