Kosmos 419, also known as 3MS No.170 was a failed Soviet spacecraft intended to visit Mars. The spacecraft was launched on 10 May 1971, but due to an upper stage malfunction, it failed to depart low Earth orbit. In 1971, Mars was at its closest to Earth since 1956, and in May of that year, both the Soviet Union and the United States made new attempts to reach the Red Planet. Kosmos 419 was intended to overtake the United States probes, Mariner 8 and Mariner 9, with the aim of becoming the first Mars orbiter. As it was, Mariner 8 was lost in a launch failure two days before Kosmos 419 was launched, and Mariner 9 went on to become the first spacecraft to orbit Mars.

Wikipedia: https://en.wikipedia.org/wiki/Kosmos_419. Original timeline Wikipedia link: https://en.wikipedia.org/wiki/Cosmos_program. Related NASA reference: https://nssdc.gsfc.nasa.gov/planetary/chronology.html#1971. Description adapted from Wikipedia contributors (CC BY-SA 4.0; https://creativecommons.org/licenses/by-sa/4.0/).