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Mission record

Sputnik 21

Also known as Alpha Pi 1, Sputnik 25 (USNSC), Sputnik21

U.S.S.R · Launched

Explore trajectory

Failed · Failure

An attempted Venus flyby. NSSDCA records that the third stage liquid oxygen valve failed to close and that 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.

Destinations
Launch vehicle
Modified SS-6 (Sapwood) with 2nd Generation Upper Stage + Escape Stage
Launch site
Tyuratam (Baikonur Cosmodrome), U.S.S.R
Countries
Soviet Union
Mission types
Flyby

Chronology

Mission timeline

  1. Launch

    Launched into Earth orbit after the third stage exploded

    The master catalog records that launch took place on 12 September at 1:40 UT and the launch/orbital information page gives 1962-09-12T01:40:00Z, recorded at minute precision because both print a whole minute. The two catalogues disagree on which piece this object is and it is recorded rather than resolved: the master catalog lists Alpha Pi 1 among the alternate names, while GCAT gives 1962 A PI 1 to Sputnik 19 as S00371 and gives this spacecraft S00389, piece 1962 A PHI 1. Source review: NSSDCA launch 01:40 UTC conflicts with the NASA history's 00:59:13 UT on September 12. The orbit page ends coverage at midnight before its own launch timestamp. Those fields are not a valid flight interval. Third-stage destruction is reported over T+530.95–531.03 seconds, not as a complete position or impulse measurement.

    Earth

  2. Mission end

    Reentered from low Earth orbit

    The launch/orbital information page gives a decay date of 1962-09-14 and the master catalog records that Sputnik 21 was left in low Earth orbit and reentered. That page disagrees with itself and the disagreement is recorded rather than resolved: its Earth-orbit row ends the epoch at 1962-09-12 00:00:00, which is both two days before the decay date printed at the head of the same page and one hour and forty minutes before the epoch start beside it.

    Earth

Mission architecture

Vehicles

  • Sputnik 21 · Spacecraft

    Destinations: Venus

Trajectory record

Trajectory dataset not yet available

Known dates and encounters do not uniquely determine a flight path. This mission’s sourced timeline is available above; no verified trajectory is currently published here.

What is needed to reconstruct this path?
  • A frame-qualified position and vector velocity at an epoch, or equivalent complete orbital elements.
  • Finer event-time constraints where required by an orbital reconstruction; the stored day/month/year precision is retained.
  • The actual failed-flight state history. Intended destinations are not evidence that the spacecraft reached them.

Provenance

Sources

Each source is listed once and labeled with the mission, event, trajectory, or destination/body context it supports.

Data verified through September 14, 2026