Zond 4, part of the Soviet Zond program and an uncrewed version of Soyuz 7K-L1 crewed Moon-flyby spacecraft, was one of the first Soviet experiments towards crewed circumlunar spaceflight. It was launched to test the spaceworthiness of the new capsule and to gather data about flights in circumterrestrial space. It was the first Soviet spacecraft to possess a computer, the 34 kg Argon 11.