Soyuz 4 (Russian: Союз 4, Union 4) was launched on 14 January 1969, carrying cosmonaut Vladimir Shatalov on his first flight. The mission successfully docked with Soyuz 5, marking the first docking of two crewed spacecraft. The craft received two crew members from Soyuz 5 via spacewalk, and returned to Earth. Three months prior, Kosmos 186 and Kosmos 188 achieved the first uncrewed docking of two Soyuz craft. The previous Soyuz flight (Soyuz 3) was also a docking attempt but failed for various reasons. The spacewalk was the only use of the Yastreb space suits. As well as mechnical docking, the crafts' electrical circuits were connected, and TASS announced the mission as the "world's first experimental cosmic station". The radio call sign of the crew was Amur, while Soyuz 5 was Baikal. This referred to the trans-Siberian railway project called the Baikal-Amur Mainline, which was in development at the time. The spacewalk crew transfer technique was intended to be repeated in the Soviet crewed lunar programs, to board the LK lunar lander design from the Soyuz 7K-LOK. The US similarly completed its first docking of two crewed spacecraft with Apollo 9 two months later.
Crew
Backup Crew
Reserve Crew
Mission parameters Mass: 6,625 kg (14,606 lb) Perigee: 205.0 km (127.4 mi) Apogee: 223.0 km (138.6 mi) Inclination: 51.73° Period: 88.72 minutes
Space walk Yeliseyev and Khrunov – EVA 1 EVA 1 start: 16 January 1969, 12:43:00 GMT EVA 1 end: 16 January 1969, 13:15:00 GMT Duration: 32 minutes
Preparations and planning
After the docking failure of Soyuz 2 and Soyuz 3 in October 1968, efforts were made to revise and improve docking procedures for Soyuz 4 and 5, including their being performed in daylight and over Soviet territory where communication with the ground was possible. The launch dates were tentatively scheduled for January 12–13, 1969. The Soyuz spacecraft for the mission were shipped to the Baikonur launch center during the fall months of 1968. Mid-winter in Kazakhstan brought about frigid conditions despite the moderate latitude of 45N and personnel accommodations at the launch center were poorly heated and insulated. Temperatures dropped to as low as -25C (-13F) and cases of influenza and frostbite were not infrequent. Several military servicemen, including four officers, died of hypothermia during a hunting trip. However, the cosmodrome was busy this January. Aside from Soyuz 4–5, two Venera probes were launched to Venus and one Zenit reconnaissance satellite during the month, an unsuccessful Proton launch of a Zond spacecraft, and preparations for the first N-1 moon rocket were under way. As soon as Venera 6 launched successfully from LC-1 on January 10, Soyuz 4's booster was rolled out to the pad. On January 13, the cosmonaut was strapped inside Soyuz 4 and readied for launch. During the countdown, ground crews discovered that the booster had a non-functional roll rate gyro. The launch was called off and the cosmonauts got out and had to wait for the problem to be fixed—it had been only two years since the disastrous on-pad explosion of a Soyuz booster from a gyroscope issue and the memory of that was still fresh. The exact problem with the gyroscope was unclear and could not be reproduced during ground tests, but may have been due to ice formation on a pad umbilical inhibiting electrical contact. However, just to be safe it was decided to replace the entire gyroscope package. Investigation of the gyroscope issue concluded that it was probably a malfunction of the ground support equipment at the cosmodrome, most of which had been in use since the Vostok program began nine years ago and was badly worn and in need of replacement. There was momentary concern that the launch escape system would not function properly due to the extreme cold as its solid rocket motor was certified to work down to -15C (5F). However, the escape tower had an insulating blanket placed over it and this would probably keep it warm enough. The motor was estimated to lose about 5% of its thrust from the low temperatures but this was still in an acceptable margin should a launch abort be necessary. On January 14, Soyuz 4 launched at 10:30 AM local time and everything worked perfectly during ascent.
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