Russian engineers have pinpointed the “most probable cause” for a dangerous malfunction of the Soyuz capsule.

The last couple of Soyuz coming back from the International Space Station have had rocky re-entries. Engineers fingered a faulty pyrotechnic bolt that was meant to separate the crew capsule from its service module. In July, the station’s crew undertook a space walk to remove the bolts.

According to Aviation Week, it appears that charged particles whizzing around the station may have been degrading an igniter wire in one of the explosive bolts. The Russian’s are planning to replace the bolt on future capsules and use a different re-entry profile that may alleviate the phenomenon.

Image: NASA TV