On August 19, 2023, the Russian Luna 25 lander crashed into the moon whilst attempting to land at the lunar south pole. What went wrong and why did this happen?
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1$\begingroup$ Well, it did land, didn't it? $\endgroup$– Jon CusterCommented Aug 7 at 18:27
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2$\begingroup$ @JonCuster it did! It just failed to stay in one piece $\endgroup$– The Rocket fanCommented Aug 7 at 18:41
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$\begingroup$ @JonCuster By that logic, so did Hakuto, Vikram, and a seemingly countless number of other failures. But hey, space is hard. $\endgroup$– Deko RevinioCommented Aug 7 at 19:54
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3$\begingroup$ More like the ground is hard. $\endgroup$– Darth PseudonymCommented Aug 7 at 23:31
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$\begingroup$ It is true that nothing walked away from the landing, so it wasn’t a ‘good’ landing. $\endgroup$– Jon CusterCommented Aug 8 at 1:16
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1 Answer
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This was caused by an onboard control unit not receiving the needed data from one of the lander's accelerometers. According to ROSCOSMOS on Telegram:
"This did not allow, when issuing a corrective pulse, to record the moment the required speed was reached and to timely turn off the spacecraft propulsion system, as a result of which its shutdown occurred according to a temporary setting,"
In other words, it was unable to detect when it reached the correct speed. This caused a burn that should have taken 84 seconds to take 127 seconds which had the effect of sending the lander on a crash trajectory. (source)