I read it in the 1980s. I'm pretty sure it was from an annual science fiction short story anthology compilation, probably from sometime in the mid 50s to mid 60s. It was written in English and nothing about the story read as though it was translated from another language.
The story was about a group of astronauts and/or possibly various types of scientists (male and female) on a spaceship with a special engine that they didn't know how to activate. Mission Control wouldn't tell them, either. The voyage was going to take a very long time. Finally, after some time several of the crew paired off and had sex and they noticed the ship seemed to travel faster when they did, taking years off their expected travel time.
Mission Control hadn't wanted to tell them that that was how to trigger the engine because they didn't want to make the astronauts uncomfortable or feel obligated to have sex or something like that. They all got very busy after that and the voyage went by very quickly.