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Venera 2MV-2 No.1, also known as Sputnik 21 in the West, was a Soviet spacecraft, which was launched in 1962 as part of the Venera programme, and was intended to make a flyby of Venus. 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. It was the second Venera 2MV-2 spacecraft, both of which failed to leave Earth orbit.
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. The rocket performed nominally up 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. The vernier thruster exploded, causing the rocket to tumble out of control. This led to the formation of bubbles in the upper stage oxidiser pump, which caused the upper stage engine to fail less than a second after ignition. It reentered the atmosphere on 14 September 1962, two days after it had been launched.
Payloads are separated by bullets ( · ), launches by pipes ( | ). Manned flights are indicated in bold text. Uncatalogued launch failures are listed in italics. Payloads deployed from other spacecraft are denoted in brackets.