Russia’s state space corporation Roscosmos has concluded that Luna-25 failed because the onboard control system did not receive required data from the accelerometer to trigger an engine shutdown at the correct time. Russia’s first lunar probe in almost 50 years, Luna-25 was trying to lower its orbit around the Moon in preparation for landing two days later, but instead crashed into the surface.

Launched on August 10 EDT (August 11 Moscow Time), Luna-25 successfully traversed cislunar space and entered orbit around the Moon on August 16, with landing scheduled for August 21.

The Luna-25 spacecraft before launch. Credit: Roscosmos

On August 19 at 2:10 pm Moscow Time, the spacecraft’s thrusters fired to move into a lower elliptical orbit, but instead of shutting off after 84 seconds they continued for 127 seconds. Communications were lost at 2:57 pm Moscow Time and Russian space officials concluded it had crashed.

NASA’s Lunar Reconnaissance Orbiter, which has been orbiting the Moon since 2009, detected a new crater on the Moon that imagery analysts believe is the crash site.

During the descent to the surface, the Russian spacecraft Luna 25 experienced an anomaly that caused it to impact into the southwest rim of Pontécoulant G crater on Aug. 19, 2023, at 7:58 a.m. EDT (11:58 a.m. UTC). This image is 1,100 meters wide, and lunar north is up. (LROC NAC frame No. M1447547309R) Photo and caption credits: NASA’s Goddard Space Flight Center/Arizona State University

On October 3, Russia’s news agency TASS reported that Roscosmos traced the problem to “the abnormal operation” of Luna-25’s “onboard control system resulting from a failure of the accelerometer unit in the BIUS-L device” that provides data on angular velocity and “the onboard control system received zero signals from accelerometers.”

Roscosmos posted a statement on the Telegram social media network (as translated by Google):

“Luna-25”: preliminary results of work to determine the reasons for the abnormal functioning of the station

On August 19, when issuing a correction pulse to transfer the spacecraft from a circular lunar orbit to an elliptical pre-landing orbit, the Luna-25 propulsion system operated for 127 seconds instead of the planned 84 seconds. As a result, the station switched to an undesigned open orbit and collided with the lunar surface.

It was established that the most likely cause of the accident was the abnormal functioning of the on-board control complex, associated with the failure to turn on the accelerometer unit in the BIUS-L device (angular velocity measurement unit) due to the possible entry into one data array of commands with different priorities for their execution by the device. In this case, the distribution of commands in data arrays is random (probabilistic) in nature.

In this regard, the on-board control complex received zero signals from the accelerometers of the BIUS-L device. 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.

Recommendations for additional activities for subsequent lunar missions have been formed.

#Moon25 #MissionMoon25

The crash was a bitter blow for Russian scientists who fought for years to get the necessary funding. Although they were never able to send people to the Moon, the Soviet Union had an impressive track record with robotic flybys, orbiters, landers and rovers in the first two decades of the Space Age, including three that returned small samples to Earth. Their last lunar probe, Luna-24 in 1976, was one of them.

In addition, two years ago Russia and China announced an International Lunar Research Station (ILRS) partnership with robotic missions in the 2020s and early-2030s leading to human exploration in the mid-2030s. Luna-25 was the first of at least four Russian probes to support ILRS. Roscosmos Director General Yuriy Borisov is vowing to proceed with the others, perhaps even accelerate their launch dates which were 2027 (Luna-26), 2028 (Luna-27) and 2030 (Luna 29).  How realistic that is considering the state of Russia’s economy because of its invasion of Ukraine remains to be seen.

China is moving ahead with ILRS and held a dedicated session on ILRS at the International Astronautical Congress this week in Baku, Azerbaijan. No one from Russia was on the panel.

Chinese officials said they’ve created an ILRS Cooperation Organisation (ILRSCO) headquartered in Hefei, China to jointly develop and manage the project. China and Venezuela recently signed an agreement for cooperation on ILRS and Space News reports that Pakistan, the UAE, the Asia-Pacific Space Cooperation Organization (which China leads), and South Africa also have agreements. The President of Turkey’s space agency was scheduled to be on the ILRS panel at the IAC, but did not attend.

Last Updated: Oct 06, 2023 6:21 pm ET