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Mission record

Cosmos 21

Also known as Cosmos21, Kosmos 21

U.S.S.R · Launched

Explore trajectory

Failed · Failure

3MV-1A was a deep-space return technology experiment. Its planned route extended 12–16 million km from Earth, outside the ecliptic, before returning after roughly six months. The actual spacecraft remained in Earth orbit after Blok L failed and reentered on November 14, 1963.

Destinations
Launch vehicle
Molniya
Launch site
Tyuratam (Baikonur Cosmodrome), U.S.S.R
Countries
Soviet Union
Mission types
Technology demonstrator, Flyby

Chronology

Mission timeline

  1. Loss of contact

    Telemetry from the Blok L upper stage lost

    The master catalog records that after launch and insertion into Earth orbit, telemetry from the Blok L upper stage was lost at about 6:45:44 UT, and that it is thought the main engine turbopump exploded upon ignition, destroying the spacecraft. Recorded at day precision because the page hedges the time itself with the word about.

    Earth

  2. Launch

    Launched into Earth orbit on a Molniya

    NSSDCA's launch/orbital information page gives the launch date and time as 1963-11-11T06:28:00Z, recorded at minute precision because the page prints a whole minute with zero seconds, and an Earth orbit with a periapsis of 182.00 km, an apoapsis of 216.00 km, a period of 88.50 minutes and an inclination of 64.800°. The master catalog prints the same time as 6:28 UT on 11 November 1963. Source review: The NSSDCA introduction is uncertain about a Venus flyby versus Earth-orbit test; its technical description and NASA history identify a deep-space return experiment. The planned route did not occur. NSSDCA launch 06:28 UTC conflicts with 06:23:34 UT in the history. Blok L telemetry loss at about 06:45:44 UT is approximate and does not resolve liftoff.

    Earth

  3. Mission end

    Orbit decayed three days after launch

    The master catalog records that the orbit decayed on 14 November, three days after launch, and the launch/orbital information page gives a decay date of 1963-11-14.

    Earth

Mission architecture

Vehicles

  • Cosmos 21 · Spacecraft

    Destinations: Venus

    • 3MV-1 No. 1 SA · Other

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.
  • Separate state histories and release epochs for the listed vehicles; a parent mission trajectory cannot be assigned to every component.
  • 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