In the Soyuz program, quite a few accidents have been caused by malfunctions of the explosive bolts:

  • Soyuz 11: Explosive bolts designed to fire sequentially fired simultaneously instead, causing a fatal malfunction of a valve.
  • Soyuz 7K-T No.39: Second and third stages of the booster did not separate properly.
  • Soyuz 5, TMA-10, and TMA-11: The service module did not separate from the reentry module

Most other Soyuz accidents seem to have been one time occurrences, but problems with the explosive bolts misfiring seem to be recurring. One would think that explosive bolts are a quite simple and robust technique, so this is a bit unexpected.

Is there an explanation for these frequent issues with explosive bolts?


1 Answer 1


This is a suggestion, I'm not sure this was the end of the story, but...

In 2008, a problem of arcing near the Pyro bolts was proposed as an explanation by the Russians.

A Pyro bolt was later retrieved from a docked Soyuz (TMA-12 -- Also here), and returned to earth for examination.

enter image description here
(source: ibid)

TMA-12 undocked with the remaining Pyro bolts and returned normally on Earth. The returned Pyro bolt examination was not conclusive, but other data existed.

According to Nasa Spaceflight Russians engineers stated:

Following the investigation, the Commission found that the most likely cause of the failure to open the latch located at “Plane I” of the interface, “was a failure of the 8 X 55 explosive bolt, caused by combined long-term exposure, under space flight conditions, to electrical discharges resulting from the difference in potential between the station hull and the surrounding plasma, which increased in magnitude after the electrical power capacity of the ISS was augmented.”

The findings relating to the long-term exposure to electromagnetic emissions on-orbit, and their potential to cause issues with the pyro bolts, came after an extensive investigation that included the removal and return of one pyro bolt from Soyuz TMA-12.

NASA confirmed somehow the assessment:

Our independent analysis agreed well with Russian provided data. Pyrotechnic and environments experts believe the stated most probable cause is possible, however unlikely in our experience.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.