Can't find the link now, but I did see Canadian Chris Hadley make a similar (less explicit) comment in his Reddit ama: https://www.reddit.com/r/IAmA/comments/1s4l7v/i_am_col_chris...
And while I'm sure people would like to think that the military have sex with each other all the time -- I'm pretty sure people manage to avoid having sex aboard submarines and other environments that are similar to a space expedition: dangerous and with long days filled with taxing work in the form of various experiments, exercises and routine tasks.