The Luna-25 station failure stemmed from an abnormal performance of its onboard control system, the BCU. This finding was issued by an interdepartmental commission and published on Roscosmos’s official site.
Investigations showed that the BIUS-L device’s accelerometer unit, which measures angular velocity, failed to activate. The fault likely arose from how command data with differing priority levels were handled, introducing randomness into the distribution of commands across data arrays. In this scenario, the onboard control complex received no signal from the accelerometer, preventing a proper corrective pulse from being recorded and timing the spacecraft propulsion shutdown accurately. As a result, the shutdown occurred based on an interim setting rather than a precise speed milestone, according to the Roscosmos message.
During the transfer from a circular lunar orbit to the elliptical pre-landing propulsion phase, the vehicle operated for 127 seconds instead of the planned 84 seconds.
Consequently, the station shifted into an open orbit beyond its design parameters and eventually collided with the lunar surface, Roscosmos reported.
To prevent a repeat in the next month’s mission, the commission issued recommendations for additional activities.
Sixteen versions examined for the disaster
Earlier, Roscosmos chief Yuri Borisov attributed the accident to the accelerometer remaining off. The agency noted that a total of 16 potential scenarios were considered, with 11 already reviewed at a September press conference.
In late August, Borisov indicated that after the Luna-25 incident Russia was evaluating another attempt to land an automatic station at the Moon’s south pole during 2025–2026. Russian designers and researchers reportedly remain enthusiastic about continuing the Moon project.
Borisov emphasized that halting the lunar program would be a grave mistake and that it would not be an option to pause the efforts. Follow-up timelines were given for the Luna-26 mission in 2027, Luna-27 in 2028, and Luna-28 in 2030 or later.
First lunar mission since 1976
The modern era of Russian lunar exploration began with Luna-25, following the last successful Soviet mission Luna-24 in 1976. The Luna-25 launch took place at the Vostochny cosmodrome in the Amur region, using the Soyuz-2.1b rocket with a Fregat upper stage.
Early objectives included soil analysis of the Moon and sustained scientific investigations. These encompassed the southern polar region’s surface, the solar wind’s influence on the body, and the study of the lunar exosphere, the outermost layer of the Moon’s atmosphere.
The spacecraft entered lunar orbit and returned initial images, including a record of a micrometeorite impact on the lunar surface. The planned landing was initially scheduled for August 21, with a note that it would occur on August 19; however, the lander collapsed upon approaching the surface.