Soyuz 21
Mission typeDocking with Salyut 5
OperatorSoviet space program
COSPAR ID1976-064A
SATCAT no.08934
Mission duration49 days 6 hours 23 minutes 32 seconds
~60 days (planned)
Orbits completed790
Spacecraft properties
SpacecraftSoyuz 7K-T No.9
Spacecraft typeSoyuz 7K-T/A9
ManufacturerNPO Energia
Launch mass6750 kg [1]
Landing mass1200 kg
Crew size2
MembersBoris Volynov
Vitaly Zholobov
CallsignБайкал (Baikal - "Lake Baikal")
Start of mission
Launch date6 July 1976, 12:08:45 UTC
Launch siteBaikonur Site 1/5[2]
End of mission
Landing date24 August 1976, 18:32:17 UTC
Landing site200 km at the southwest of Kokshetau, Kazakhstan
Orbital parameters
Reference systemGeocentric orbit[3]
RegimeLow Earth orbit
Perigee altitude193.0 km
Apogee altitude253.0 km
Period88.7 minutes
Docking with Salyut 5
Docking date7 July 1976
Undocking date24 August 1976
Time docked48 days

Vimpel Diamond patch  

Soyuz 21 (Russian: Союз 21, Union 21) was a 1976 Soviet crewed mission to the Salyut 5 space station, the first of three flights to the station.[4] The mission's objectives were mainly military in scope, but included other scientific work. The mission ended abruptly with cosmonauts Boris Volynov and Vitaly Zholobov returning to Earth after 49 days in orbit. The precise reason for the early end of the mission was the subject of much speculation, but was reported to be an emergency evacuation after the Salyut atmosphere developed an acrid odor.


Position Cosmonaut
Commander Soviet Union Boris Volynov
Second and final spaceflight
Flight Engineer Soviet Union Vitaly Zholobov
Only spaceflight

Backup crew

Position Cosmonaut
Commander Soviet Union Vyacheslav Zudov
Flight Engineer Soviet Union Valery Rozhdestvensky

Reserve crew

Position Cosmonaut
Commander Soviet Union Viktor Gorbatko
Flight Engineer Soviet Union Yury Glazkov

Mission parameters

Mission highlights

Salyut 5, the last dedicated military space station in the Soviet space program,[5] was launched 22 June 1976. Its first crew was launched 14 days later on 6 July 1976, with Commander Volynov and Flight Engineer Zholobov aboard Soyuz 21. Based on landing opportunities, observers estimated the mission was intended to last 54 to 66 days.[5] They docked with the station the next day, and gave a televised tour 8 July 1976.[5]

Their stay coincided with the start of the Siber military exercise in Siberia, which they observed as part of an assessment of the station's military surveillance capabilities. They conducted only a few scientific experiments, including the first use of the Kristall furnace for crystal growth. Engineering experiments included propellant transfer system tests with implications for future operation of the freight-carrying Progress spacecraft.

Experiments conducted during the mission were mainly of a military nature as part of the Almaz program. Various purely scientific tasks were also carried out, including solar observations and biological observations of an aquarium of fish carried into orbit.[5] A television link-up with school children on 17 August 1976 was also undertaken.[5]

On 24 August 1976, it was announced the mission was to end in only 10 hours, a development which caught even the reporters of Radio Moscow by surprise.[5] The reason for the sudden termination of the mission was reported at the time to have been an acrid odor that developed in the environmental control system. The problem was said to have begun as early as 17 August 1976.[5] The Soviets made no comments at the time, but the next crew to board the station wore breathing masks.[6] Later reports indicate that the mission may have ended owing to a deterioration in the health of Zholobov. The mission was to last two months but was cut short by a gradually worsening illness of Zholobov.[1]

The cosmonauts boarded Soyuz 21 but as Volynov tried to undock from the station, the docking latches failed to release properly. As he fired the jets to move the spacecraft away, the docking mechanism jammed, resulting in the Soyuz being undocked but still linked to Salyut. As the two spacecraft moved out of range of ground communications, the cosmonauts received only the first set of emergency procedures. Volynov tried a second time to undock but only managed slightly to loosen the latches. The situation persisted for an entire orbit, 90 minutes, when the final set of emergency procedures were received and the crew finally disengaged the latches.

Because Soyuz 21 was returning early, it was outside the normal recovery window. It then encountered strong winds as it descended, which caused uneven firing of the retrorockets. It made a hard landing around midnight 200 km (120 mi) at the southwest of Kokchetav, Kazakhstan.[1]

Zholobov's illness was apparently caused by nitric acid fumes leaking from the Salyut's propellant tanks; other reports, however, indicate that the crew failed to follow their physical exercise program and suffered from lack of sleep.[7] Sources at NASA have reported that psychologists with the Russian Aviation and Space Agency cited Soyuz 21 as ending prematurely due to unspecified "interpersonal issues" with the crew.[8] The next mission to successfully dock with the station, Soyuz 24, would vent Salyut 5's air to space and replace it due to concerns the air had become toxic.


  1. ^ a b c d "Display: Soyuz 21 1976-064A". NASA. 14 May 2020. Retrieved 14 October 2020. Public Domain This article incorporates text from this source, which is in the public domain.
  2. ^ "Baikonur LC1". Encyclopedia Astronautica. Archived from the original on 15 April 2009. Retrieved 4 March 2009.
  3. ^ a b "Trajectory: Soyuz 21 1976-064A". NASA. 14 May 2020. Retrieved 14 October 2020. Public Domain This article incorporates text from this source, which is in the public domain.
  4. ^ The mission report is available here:
  5. ^ a b c d e f g Newkirk, Dennis (1990). Almanac of Soviet Manned Space Flight. Houston, Texas: Gulf Publishing Company. ISBN 0-87201-848-2.
  6. ^ Clark, Phillip (1988). The Soviet Manned Space Program. New York: Orion Books, a division of Crown Publishers, Inc. ISBN 0-517-56954-X.
  7. ^ Hall, Rex; David Shayler (2003). Soyuz: A Universal Spacecraft. Springer. pp. 195–196. ISBN 1-85233-657-9.
  8. ^ Burrough, Bryan (1998), Dragonfly: NASA and the Crisis Aboard Mir, HarperCollins, p. 185, ISBN 0-88730-783-3