This pin is about the Vostok Space Program flights 5 and 6. The Vostok Space Program was a Soviet human spaceflight project to put the first Soviet citizens into low earth orbit and return them safely to earth.
They succeded because the first Vostok flight (Vostok 1) put the first human in space in 1961. That man was Yuri Gagarin.
In total the Vostok project made 6 space flights and this pin is about flights 5 and 6. Flights 5 and 6 were in space at the same time and they orbited very close to eachother establishing radio contact. Flight 6 put the first woman in space. She was called Valentina Tereshkova.