Soyuz-9 on the 1971 USSR commemorative stamp "424 hours On Earth's Orbit"
Commander Andrian Nikolayev and flight-engineer Vitaly Sevastyanov spent eighteen days in space conducting various physiological and biomedical experiments on themselves, but also investigating the social implications of prolonged spaceflight. The cosmonauts spent time in two-way TV links with their families, watched the World Cup football game, played chess (including this chess game with the crew as white; it was the first chess game played across space) with ground control, and voted in a Soviet election. The mission set a new space endurance record and marked a shift in emphasis away from spacefarers merely being able to exist in space for the duration of a long mission (such as the Apollo flights to the moon) and being able to live in space.
On their return to Earth, the crew was found to have weakened considerably, and it took some ten days for them to regain their strength. In orbit, they had sacrificed some of their exercise time for the sake of carrying out their scientific work, and their bodies' reactions to the prolonged weightlessness emphasised the importance of maintaining regular exercise.