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Comment by azernik | Hacker News Reader

The LES is the only way the capsule can separate from a malfunctioning booster. That activation happened to be on the ground, so the ballistic trajectory was rather short and dominated by the velocity the LES itself imparted; but activate it for an in-flight failure like this one and you will be off on a more substantial suborbital trajectory.

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This is false. LES tower jettison was prior to the failure today.

https://www.youtube.com/watch?v=bIxkVAXPYPc&t=134

I'm not sure about that - the NASA commentator says the LES tower was jettisoned pretty much at the time the booster appears to have failed. From her later comment, she doesn't seem to have seen that a failure happened until some time afterwards, even though the Russian's are clearly saying a failure happened, so I think she's reading from a script of what should be happening at that moment. So I would not treat her saying the LES tower jettison occurred as being certain.

I agree with your interpretation of the tape audio, but the 'ballistic trajectory' statements from Roscosmos/NASA tell us that it was not rocket-powered. Indications are that the anomaly happened at booster sep, which is a few seconds after LES jettison.

http://www.russianspaceweb.com/soyuz_launch.html

That page says LES can be jettisoned on either side of separation depending on flight profile.

The tower is not the only component of the Soyuz LES - after the extra thrust is needed, the tower is jettisoned and the LES relies on the engines in a "shroud" around the capsules.

See the first segment in this video for an explanation of the system: https://www.youtube.com/watch?v=QMUJ004Dr8Q

It sounds like you are right.

To add to the other poster, while the LES was jettisoned, in this case it seems that the booster failed to ignite, which allowed normal staging separation.

That's not right. The stage sep was the Soyuz strap-on boosters separating from the sustainer stage. It was already ignited.

Just the tower, not the whole LES. See this video for an illustration of this rather exotic system: https://www.youtube.com/watch?v=QMUJ004Dr8Q

There is no ignition on Soyuz, because they couldn't find a reliable way to ignite the engine when it was designed so second stage works from the start, it is the central part of the rocket, and 4 boosters around it.

Second stage was shut down because of the problems with a booster separation.

The other way (which is what happened here) is simply detaching from the booster using the normal mechanism.

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