A last-moment sensor malfunction doomed this Soviet Moon landing attempt.

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The first attempt to launch this vehicle took place at 07:05:36 UT on Sept. 4, 1965, but the launch was aborted due to a problem in a sensor that measured relative velocity on the rocket.

The subsequent launch a month later went off successfully and the Blok L upper stage sent Luna 7 on its way to the Moon. Unlike its predecessors, Luna 7 successfully carried out its mid-course correction on Oct. 5, 1965 on the way to the Moon in anticipation of a soft-landing two days later (at the time planned for 2208 UT on Oct. 7, 1965).

Unfortunately, immediately prior to a planned retro-fire during the approach to the lunar surface, the spacecraft suddenly lost attitude control and failed to regain it. One of its attitude control sensors the one designed to lock onto Earth stopped functioning, preventing it from reaching the desired orientation for firing its retro-engine.

Automatic programmed systems then prevented the main engine from firing. As controllers observed helplessly, Luna 7 plummeted to the lunar surface at a very high speed, crashing at 22:08:24 UT on Oct. 7, 1965 west of the Kepler crater, relatively near to the actual intended target.

Impact coordinates were 9 degrees north latitude and 49 degrees west latitude. Later investigation indicated that the optical sensor of the Yupiter-M astronavigation system had been set at the wrong angle and had lost sight of Earth during the critical attitude control maneuver. It was the tenth consecutive failure in the Ye-6 program.

Source

Siddiqi, Asif A. Beyond Earth: A Chronicle of Deep Space Exploration, 1958-2016. NASA History Program Office, 2018.

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