"With the prospect of a very long-term mission, it's hard to ignore the question of sexuality," says Lawrence Palinkas, a medical anthropologist at the University of Southern California in Los Angeles, an author of the report.

Palinkas says long-term space missions may be similar to extended periods in the isolated and confined environments of Antarctic research stations. He says crews in those stations often pair up in "bachelor marriages" that last the length of their stay – or less. "If there are instances of sexual conflict or infidelity, that may lead to a breakdown in crew functioning.

Sexual harassment may also endanger a mission. In an 8-month space station simulation on Earth in 2000, a Russian man twice tried to kiss a Canadian woman researcher just after two other Russians had gotten into a bloody brawl. As a result, locks were installed between the Russian and international crews' compartments.