Russia’s Luna-25 Crash Traced To Onboard Control Issue

BAKU, Azerbaijan—Russia’s attempt to land a spacecraft on the Moon in August—its first lunar mission in nearly 50 years—failed due to a mistimed thruster burn that lasted 127 sec. instead of 84 sec. caused by a malfunctioning onboard control system.

The Luna-25 thruster failed to switch off when the spacecraft reached the planned speed because an onboard computer received no data from the accelerometer unit in the BIUS-L angular velocity measurement block, Russian State Space Corp. Roscosmos said Oct. 3.

“The accelerometer failed to activate due to the possibility of conflicting data commands with different execution priorities. The thrusters worked 127 sec. instead of the planned 84 sec.,” Roscosmos added.

The 1,750-kg (3,860-lb.) Luna-25 had been targeted to touch down around the Boguslawsky crater near the Moon’s south pole. But instead it crashed into the southwest rim of the Pontecolaunt G crater on Aug. 19 after failing to reach a prelanding elliptical orbit, ending the 10 billion ruble ($101 million) mission.

As a result of the accident, Russia is rescheduling follow-on missions.

Russia has planned three more missions: Luna-26, 27 and 28, initially slated for 2027, 2028 and 2030. A fourth mission, Luna-29, is expected after 2030.

The Luna-26 orbiter will be delayed for a year for additional checks of ground and spacecraft computer interfaces, Lev Zeleny, academic advisor with Russia’s Space Research Institute, said Oct. 3 at the International Astronautical Congress here.

The Luna-25 thruster issue resulted from a malfunction in the interface between the primary ground computer and the spacecraft’s computer, Zeleny noted.

The primary goal of the Luna-26 mission will be to survey possible landing sites for the Luna-27 and 28 missions.

The Luna-27 lander will take into account all lessons from the failed Luna-25 mission, Zeleny said. “We think about making two copies of the spacecraft for redundancy like in the Soviet times,”  he added.

Soviet-era lunar spacecraft were dispatched in pairs in case one failed.

The Space Research Institute has already begun scouting potential landing zones on the Moon’s south pole for Luna-27, which will explore water deposits in the lunar soil at depths of 1-1.5 m (3.3-5 ft.) with cryogenic drilling.

Luna-27 will use the Luna-26 orbiter as a relay satellite. “I think we can also use Chinese lunar orbiters for relay services,” Zeleny added.

 Russia and China signed an agreement on joint lunar exploration in 2021. China plans to deploy the Queqiao-2 relay satellite in lunar orbit in 2024 to support its upcoming Chang’e 6, 7 and 8 missions.

Additional cryogenic drilling will continue with Russia’s Luna-28 mission, which will also test high-precision landing techniques and sample-return capability.