Pierre Kohler, a respected French scientific writer, says in [his book] The Final Mission: Mir, The Human Adventure that the subject is taboo both at NASA and at Mission Control in Moscow, but that cosmic couplings have taken place.
...He cites a confidential NASA report on a space shuttle mission in 1996. A project codenamed STS-XX was to explore sexual positions possible in a weightless atmosphere.
(Geez, couldn't it've been STS-XXX? Hi, I'm juvenile.)