(Rimshot!)

Not to worry, man (and woman) will find a way. There’s not much else to do on a really long mission.

But seriously, there are all sorts of problems here. Sex is much more than a physical release or a reproductive function. It also serves an important human bonding element. There is a vital emotional component.

Can healthy, attractive, capable young people be cooped together for long periods of time and avoid sexual relationships? Sexual bonding is a positive thing, but what about relationships breaking up, jealousy, infidelity, promiscuity, and a host of other issues, both social and psychological. And all in a cramped, isolated environment where everyone depends on each other to survive. Human culture on earth has developed elaborate structures to deal with these problems, and not too successfully, I might add. Enforced celibacy will impose a whole different set of tensions.

The starship crew may resemble the small hunter-gatherer band, so that form of primate sexual politics (as described by anthropologists) would probably work very well in space. After all, we are probably evolutionarily wired for precisely that arrangement. But culture had to dismantle all that when we settled down on farms and cities, causing all sorts of dysfunction. Unfortunately, the crews would not have been socialized in small tribal groups, they grew up in modern civilizations. They may not want to or be able to adapt to a neolithic sexual organization.

Lots of potential problems here.