[4] Due to a problem with the rocket which launched it, it failed to leave low Earth orbit, and reentered the atmosphere a few days later.
[3] Venera 2MV-2 No.1 was launched at 00:59:13 UTC on 12 September 1962, atop a Molniya 8K78 carrier rocket flying from Site 1/5 at the Baikonur Cosmodrome.
[2] The rocket performed nominally until cutoff of the Blok I stage, following injection into a low Earth orbit.
Following cutoff, one of the oxidiser valves failed to close, and liquid oxygen was allowed to flow into the combustion chamber of one of the vernier thrusters.
[7] The designations Sputnik 25, and later Sputnik 21, were used by the United States Naval Space Command to identify the spacecraft in its Satellite Situation Summary documents, since the Soviet Union did not release the internal designations of its spacecraft at that time, and had not assigned it an official name due to its failure to depart geocentric orbit.