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Mission record

Cosmos 21

Also known as Cosmos21, Kosmos 21

U.S.S.R · Launched

Explore trajectory

Failed · Failure

A flight NSSDCA has tentatively identified as a technology test of the Venera series space probes, which may have been an attempted Venus flyby presumably similar to the later Cosmos 27 mission, or may have been intended from the beginning to remain in geocentric orbit. In either case the spacecraft never left Earth orbit after insertion by the SL-6/A-2-e launcher: telemetry from the Blok L upper stage was lost at about 6:45:44 UT, and it is thought the main engine turbopump exploded upon ignition. NSSDCA records this as the first time the Soviet Union used the Cosmos designation for a mission that failed and remained stranded in Earth orbit.

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.

    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

No verified trajectory dataset is committed for this mission, so Mission Atlas renders no path.

Provenance

Sources

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

Data verified through September 3, 2026