NASA Logo, National Aeronautics and Space Administration
NASA Space Science Data Coordinated Archive Header

Cosmos 21



This mission has been tentatively identified as a technology test of the Venera series space probes. It may have been an attempted Venus flyby, presumably similar to the later Cosmos 27 mission, or it may have been intended from the beginning to remain in geocentric orbit. In any case, the spacecraft never left Earth orbit after insertion by the SL-6/A-2-e launcher. The orbit decayed on 14 November, three days after launch.

Spacecraft and Subsystems

Cosmos 21 used the Soviet 3MV-1 design, for Venus impact missions, but this was designated 3MV-1A, indicating a technology test in which the probe would go into deep space and return. The main bus was 3.6 meters tall and 1.1 meter in diameter. It comprised two sealed compartments. Total mass was about 800 kg.

The spacecraft was propelled by a S5.45 main engine, capable of two firings, and had a KDU-414 engine for mid-course corrections. The spacecraft carried UDMH and nitric acid fuel for the mid-course correction engine. Power was supplied by 4 meter long solar panels charging a 14 volt, 112 amp-hour battery. It had 32 cm transmitters and 1 m receivers, with a 2 meter diameter high gain antenna. Earth, Sun, and start trackers were used for navigation. Two tape recorders were on-board for storage and retransmission of data.

Cosmos 21 carried a number of scientific instruments and technology tests, including a radiation detector, charged particle detector, magnetometer, piezoelectric detector, LA-2 atomic hydrogen detector, Kassiopeya radio telescope, RSK-2M ultraviolet and Roentgen solar radiation experiment, VIKT-2 vapor friction technology test, and plasma engines.

Mission Profile

After launch on 11 November 1963 at 6:28 UT and insertion into Earth orbit, telemetry from the Blok L upper stage was lost at about 6:45:44 UT. It is thought the main engine turbopump exploded upon ignition, destroying the spacecraft. The mission was designated Cosmos 21 after failing to leave Earth orbit. This was the first time the Soviet Union used the "Cosmos" designation for a mission that failed and remained stranded in Earth orbit.

Beginning in 1963, the name Cosmos was given to Soviet spacecraft which remained in Earth orbit, regardless of whether that was their intended final destination. The designation of this mission as an intended planetary probe is based on evidence from Soviet and non-Soviet sources and historical documents. Typically Soviet planetary missions were initially put into an Earth parking orbit as a launch platform with a rocket engine and attached probe. The probes were then launched toward their targets with an engine burn with a duration of roughly 4 minutes. If the engine misfired or the burn was not completed, the probes would be left in Earth orbit and given a Cosmos designation.

Alternate Names

  • 00687
  • Cosmos21
  • Kosmos 21

Facts in Brief

Launch Date: 1963-11-11
Launch Vehicle: Molniya
Launch Site: Tyuratam (Baikonur Cosmodrome), U.S.S.R
Mass: 890 kg

Funding Agency

  • Unknown (U.S.S.R)


  • Planetary Science

Additional Information

Questions and comments about this spacecraft can be directed to: Dr. David R. Williams



NameRoleOriginal AffiliationE-mail

Selected References

  • Shelton, W., Soviet space exploration - the first decade, Arthur Barker Ltd., Unnumbered, London, England, 1969.
  • Harvey, B., The new Russian space programme from competition to collaboration, John Wiley and Sons, Chichester, England, 1996.
[] NASA Logo -