A NASA document on crew health shows how the agency is pondering some of the ethical questions raised by deep space exploration. I was again reminded of Heinlein's Stranger In A Strange Land as I read that sex would be dealt with separately: the book opens with, oddly enough, a look at a manned mission to Mars and the associated, seemingly-thorough screening process to select the crew. The mission ends in tragedy because of... you guessed it: sex.
I'm not suggesting that NASA will overlook this - the article suggests that sex will be considered under the category of behavioural issues. This is just one of those top-of-the-head posts.