Espionage in the Space Race

During the space race (let's say 1956 to 1969, US and USSR), were there any advances in space exploration technology that were stolen by the other side?I've read a lot about espionage in military and diplomatic areas, but I've never found anything about non-military space-related espionage. It seems that, in such a prestige-awarding contest, both countries would be eager to spy on what the other was doing....Read more