Cosmonaut Andriyan Nikolayev orbited the Earth 64 times in Vostok 3 over nearly four days in space, August 11–15, 1962, a feat which would not be matched by NASA until the Gemini program (1965–1966).

The flight was terminated early after a misunderstanding by ground control, who believed that Popovich had given them a codeword asking to be brought back ahead of schedule.

This condition was unknown at the time, leading Soviet scientists to devote efforts to study the effect of spaceflight on the human body.

Plans for a three-day mission only went forward when the approval of Soviet Premier Nikita Khrushchev was obtained; in the end, Vostok 3 would last nearly four days.

The close orbits of the two spacecraft would keep the number of variables to a minimum, allowing the measurement of individual differences in adaptation to spaceflight.

[12] Informed by Titov's experience in Vostok 2, Nikolayev and Popovich thoroughly rehearsed their spacecraft maneuvers and other planned activities in a simulator.

[8] The Vostok 3/4 flights were originally scheduled for November 1961, which would have had the propaganda value of the Soviet program having flown four men in space along with a dual mission in the same calendar year when the United States had yet to orbit a single man, but Korolev's plans were frustrated by the Zenit photo reconnaissance satellite program which needed to use the R-7 pads at Baikonur.

[9] By mid-July, the pad had been restored to use, but another delay occurred when the United States carried out a high-altitude nuclear test on 9 July known as Starfish Prime.

The former adjusted his spacecraft's orientation to watch the launch, but failed to see anything despite reporting considerable details on the ground as he had passed over Turkey.

Both Nikolayev and Popovich spent time out of their seats each day, conducting a series of tests to determine their ability to maneuver and work in conditions of weightlessness.

The results of the tests were deemed positive, evidence of the ability of humans to function and work over longer periods in microgravity.

[12] Nikolayev also spoke with Soviet Premier Nikita Khrushchev over the radio, but interference was so bad that he couldn't hear most of the conversation.