Luna 25 crash most likely caused by abnormal functioning of onboard control system - Roscosmos

MOSCOW. Oct 3 (Interfax) - The crash of Russia's Luna 25 moon-landing mission was most likely caused by the abnormal functioning of its onboard control system after the accelerometer block failed to switch on, thus preventing the timely shutdown of the spacecraft's engines, Roscosmos said.

"It was established that the most likely reason behind the Luna 25 disaster was the abnormal functioning of the onboard control system after the accelerometer block in the BIUS-L [angular velocity measurement block] failed to switch on because of a possible input of commands with various priorities in the same data array," the Roscosmos press service said on Tuesday, commenting on the preliminary results of the investigation into the Luna 25 crash.

Distribution of commands in data arrays is "probabilistic", it said.

"The onboard control system received zero signals from the BIUS-L accelerometers. This did not allow to record the moment of gaining the required speed when inputting the corrective pulse and to timely switch off the spacecraft's engines, which resulted in their shutdown according to the timed settings," Roscosmos said.

Luna 25, the first lunar landing mission in Russia's post-Soviet history, lifted off aboard a Soyuz-2.1b launch vehicle with a Fregat upper stage from Vostochny Cosmodrome on August 11.

The spacecraft's soft landing on the Moon's South Pole was supposed to take place on August 21, but the lander was lost on August 19 after crashing into the lunar surface.

On August 21, Borisov said that the Luna 25 engine's failure to shut down properly for the lander's crash. "Instead of the planned 84 seconds, it worked for 127 seconds. This was the main cause of the lander's crash", he said.

On August 25, Borisov said that Russia was considering making another attempt to land at the lunar South Pole in 2025-2026 despite the Luna 25 crash.

Russia should not interrupt its lunar program and should remain in the lunar race in order to achieve technological sovereignty, he said.

On August 11, Borisov said that Roscosmos plans to launch the Luna 26 mission in 2027, Luna 27 in 2028, and Luna 28 by 2030 or later.