Vostok 4 (Russian: Восток-4, Orient 4 or East 4) was a mission in the Soviet space program. It was launched a day after Vostok 3 with cosmonaut Pavel Popovich on board—the first time that more than one manned spacecraft were in orbit at the same time. The two Vostok capsules came within 6.5 km (4.0 mi) of one another and ship-to-ship radio contact was established.
The cosmonauts of Vostok 3 and 4 did not attempt rendezvous. At one point the craft came within a few kilometers of each other and Popovich later reported at a news conference that he saw the other craft from orbit. Popovich is quoted as saying, "I saw it at once," referring to seeing Vostok 3 in orbit. "It looked like a very small moon in the distance."
The Vostok 3 and 4 spacecraft landed about 200 km apart, south of Karaganda, Kazakhstan.
The mission went largely as planned, despite a malfunction with the Vostok's life-support systems that meant that cabin temperature dropped down to 10 °C (50 °F). 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.
The re-entry capsule is now on display at the NPO Zvezda Museum in Moscow, but it has been modified to represent the Voskhod 2 capsule.