Leonard David's INSIDE OUTER SPACE

Credit: NPO Lavochkin

That failed Russian Luna-25 robotic lunar lander was likely taken out by out-of-whack accelerometer hardware, part of the BIUS-L component that provides angular velocity measurements.

Russia’s rekindling of its lunar program following the former Soviet Union’s pioneering Moon exploration initiatives that ended in 1976 will move forward, according to Roscosmos chief, Yuri Borisov.

During preparations for descent to the surface, Russia’s Luna-25 Moon lander 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).
Image credits: NASA’s Goddard Space Flight Center/Arizona State University

In a look into the Luna-25 mishap, the craft’s propulsion system on August 19 operated for 127 seconds instead of a planned 84 seconds – an incorrect propulsive maneuver that sent the lander onto a crashing finish on the Moon.

On August 19 that impulse was meant to form the probe’s pre-landing elliptical orbit. However, communication with the automatic station was interrupted. A subsequent search for Luna-25 did not produce results.

Post-crash photo shows Roscosmos chief, Yuri Borisov inspecting Luna-25 test facility. Image credit: Roscosmos

Abnormal functioning

According to a Roscosmos posting, the culprit 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.”

Image credit: Roscosmos/Lavochkiin/IKI

The on-board control complex received zero signals from the accelerometers of the BIUS-L device. Reportedly, this hardware had not been previously flown under actual space conditions.

“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,” the Roscosmos Telegram communiqué adds.

Russian mishap group dug into why Luna-25 mission failed.
Image credit: Roscosmos

Moving forward

Recommendations to avoid a similar issue on subsequent lunar missions have been formulated.

At the now-underway International Astronautical Congress meeting in Baku, Yuri Borisov also reported that the interdepartmental commission to determine the reasons for the abnormal functioning of the Luna-25 automatic station had completed its work and that a report was being prepared to the Government of the Russian Federation.

Luna-26
Image credit: Roscosmos/IKI/Inside Outer Space archives

Roscosmos is considering the option of carrying out flights of the Luna-26 and Luna-27 missions at an earlier date.

Luna-27
Image credit: Roscosmos/IKI/Inside Outer Space archives

“No one is going to fold their arms, and we are determined to continue the lunar program. Moreover, we are considering the possibility of shifting the Luna-26 and Luna-27 missions to the left in order to get the results we need as quickly as possible,” Borisov said.