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Sputnik 21



Sputnik 21 was an attempted Venus flyby mission. Launch took place on 12 September at 1:40 UT. The third stage liquid oxygen valve failed to close, and 531 seconds after launch the SL-6/A-2-e third stage exploded and broke into seven pieces. It still put the craft into Earth orbit, but the engine pump failed when the burn started to head for Venus, and Sputnik 21 was left in low Earth orbit and reentered.

This spacecraft was originally designated Sputnik 25 in the U.S. Naval Space Command Satellite Situation Summary.

Alternate Names

  • 00389
  • Alpha Pi 1
  • Sputnik 25 (USNSC)
  • Sputnik21

Facts in Brief

Launch Date: 1962-09-12
Launch Vehicle: Modified SS-6 (Sapwood) with 2nd Generation Upper Stage + Escape Stage
Launch Site: Tyuratam (Baikonur Cosmodrome), U.S.S.R
Mass: 6500 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.
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