Zond 3MV-1 No.2 (or Zond 3MV-1A No. 4A ), also known as Venera 1964A in the West, was a Soviet spacecraft, which was launched in 1964 as part of the Zond program. Due to a problem with its carrier rocket third stage, it failed to reach low Earth orbit. Zond 3MV-1 No.2 was launched at 05:47:40 UTC on 19 February 1964, atop a Molniya 8K78M carrier rocket flying from Site 1/5 at the Baikonur Cosmodrome. The launch started nominally, however, the third stage failed. A subsequent investigation concluded that an unpressurised valve (B4311-O) allowed LOX (liquid oxygen) to leak and come in contact with the RP-1 propellant while the rocket was still on the launchpad.

Wikipedia: https://en.wikipedia.org/wiki/Venera_1964A. Original timeline Wikipedia link: https://en.wikipedia.org/wiki/Venera_program. Related NASA reference: https://nssdc.gsfc.nasa.gov/planetary/tent_launch.html#venera1964a. Description adapted from Wikipedia contributors (CC BY-SA 4.0; https://creativecommons.org/licenses/by-sa/4.0/).