That works out well for space travel, given that older people have less time left in their lives for space radiation to potentially cause cancer, Kring said.

CNN: 501 days in space with your spouse: Could you handle it?

Friends who have known each other for decades, or siblings who get along well and are comfortable spending long periods of time with one another, would also be suitable for this sort of situation, said Jason Kring, assistant professor at Embry-Riddle Aeronautical University, who is not involved with the mission.

CNN: 501 days in space with your spouse: Could you handle it?