The Soyuz-FG booster incident occurred after a sensor that signals the separation of the first and second stages was deformed during the rocket’s assembly at the Baikonur Cosmodrome, Head of the Emergency Commission, Deputy Director of the Central Research Institute of Machine-Building (TsNIImash) Oleg Skorobogatov said on Thursday.

"The nozzle lid of the oxidizer tank in the block D did not open as a sensor of the stages’ separation was deformed (a 6-degree bend) during the assembly of the ‘package’ at the Baikonur Cosmodrome, which was the cause of the off-nominal separation," Skorobogatov said.

According to the commission head, "this has been proven and confirmed documentarily that this occurred due to the faulty sensor and this could occur only during the assembly of the ‘package’ at the Baikonur Cosmodrome.’"

A Soyuz-FG carrier rocket with a manned Soyuz MS-10 spacecraft blasted off from Kazakhstan’s Baikonur Cosmodrome to the International Space Station (ISS) on October 11. On board the spacecraft were Russian cosmonaut Alexei Ovchinin (the commander of the Soyuz MS-10) and NASA astronaut Nick Hague.

Following a smooth liftoff, the Soyuz’s booster malfunctioned between the first and second stages of separating, whereupon the crew was forced to abort the flight and switch to ballistic descent. The manned Soyuz MS-10 spacecraft ended up landing in the Kazakh steppe.

The press office of Russia’s Central Military District reported that rescuers recovered the crew from the descent capsule. Later, the crewmembers were examined and found to be in good condition. After their medical check-up in the town of Baikonur, the astronauts were transported to Moscow.

This is the first emergency landing with this type of carrier rocket over the past 35 years.

NASA astronaut Nick Hague, who returned to Moscow from the Baikonur spaceport on October 12 after the Soyuz booster’s failure, flew to the United States on October 13.