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I just watched the live feed of the Soyuz capsule landing in Kazakhstan. All the way down the narrator was describing the expected sequence of parachutes and how retro-rockets would fire approximately 3 seconds before touchdown to soften the landing.

If these rockets fired it was not visible from the long range camera footage (posted here on Twitter). If anything there is a <0.2sec window in the clip where they might have fired right at touchdown. 1 frame is in the air, 2 have a blast ring/glow, and the next is on the ground in what seems like a pretty hard touchdown.

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No mention of this is being made in the rest of the broadcast. (Edit: A narrator just described the replay about 20 minutes later saying the "there we see the soft landing engines firing just a second or two before landing", but this is neither the 3 seconds that was expected nor is it accurate as what is visible happens only a fraction of a second before touchdown.)

Was there a problem with the altitude detection or timing of the soft landing rockets firing? Would this have been visible if they had fired earlier? Or might they have fired and we just couldn't see them from this camera show? Is there other footage to compare how this sequence looks?

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  • $\begingroup$ This aerial view makes it pretty clear the rockets did fire, but the question about timing remains? Was that when they were supposed to fire and was it as soft a landing as it could have been? $\endgroup$
    – Caleb
    Commented Apr 10, 2017 at 13:07
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    $\begingroup$ The conventional wisdom is that Soyuz landings aren't as rough as they look. The landing rockets throw up alot of dust from the dry Kazakh desert. This blast indeed looks very late, but the crew seems to be okay. Cosmonauts have been through worse Soyuz 7K-ST "Upon being greeted by recovery crews, they immediately asked for cigarettes to steady their nerves. The cosmonauts were then given shots of vodka to help them relax." $\endgroup$
    – LocalFluff
    Commented Apr 10, 2017 at 13:35
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    $\begingroup$ @LocalFluff I suspect a quick release mechanism would just be one more thing that could fail during deploy. After the reentry and landing a little tip and drag is probably no sweat for anybody and not worth introducing risk to avoid. $\endgroup$
    – Caleb
    Commented Apr 10, 2017 at 14:30
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    $\begingroup$ @LocalFluff: the ESA training video I posted in my answer explains that parachute detachment is initiated manually by the commander. Maybe he lost his pointing stick thingy in the landing and it took him a couple of moments to find it again. $\endgroup$
    – Jörg W Mittag
    Commented Apr 10, 2017 at 16:26
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    $\begingroup$ @SF. Per the current answers, that's also wrong. If you have more accurate information please post an answer. $\endgroup$
    – Caleb
    Commented Apr 11, 2017 at 19:43

4 Answers 4

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ESA has a nice 3-part video series on YouTube that explains on a high-level ascent, rendezvous, and re-entry. These are actual training videos that are shown to ESA astronauts during their training.

The narrator in the video gives the height at which the retro-rockets fire as "70 cm":

70 cm above the ground, the six retro-rockets fire to further reduce the capsule's speed to approximately 5 km/h.

You can see in the video (at about 18:07) that the rockets really do fire very late and very short. It actually looks more like a small explosion underneath the capsule than sustained thrust from a rocket:

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    $\begingroup$ Does that mean the puff of smoke we saw was from the soft-landing rockets rather than from a shallow crater that formed on Soyuz impact? That would make more sense than what I thought happened. $\endgroup$
    – John Dvorak
    Commented Apr 10, 2017 at 19:23
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The "three second" item is incorrect. In general (and this can be confirmed by watching multiple landings), the rockets fire approximately half a second before landing. Maybe they meant to say "three feet"?

As an aside, astronauts who have ridden the Soyuz home invariably describe it as a fairly wild ride. Terms I've personally heard include "car accident" and "going over Niagara Falls in a barrel.... that's on fire."

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    $\begingroup$ How have the the space tourists described it? $\endgroup$
    – LocalFluff
    Commented Apr 10, 2017 at 14:08
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    $\begingroup$ 3 meters maybe? That's a possible slip up I guess although feet would be pretty small. It would be nice to read some documentation on this issue even though this circumstantial evidence makes sense. $\endgroup$
    – Caleb
    Commented Apr 10, 2017 at 14:26
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    $\begingroup$ @LocalFluff I've never met one. $\endgroup$
    – Tristan
    Commented Apr 10, 2017 at 15:57
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    $\begingroup$ @Caleb 3 meters seems awfully high to only be half a second before impact. That would be quite the jolt indeed. $\endgroup$
    – Tristan
    Commented Apr 10, 2017 at 16:00
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    $\begingroup$ @Tristan Did you watch the footage? The gap to the ground is closing pretty fast. 6m/s seems low for eyeballing the speed. If it peels off momentum it's in the final fractions of a second. Otherwise it really does look like quite a jolt. $\endgroup$
    – Caleb
    Commented Apr 10, 2017 at 16:04
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I found a book about solid fuel engine design (in Russian)

According to this book, the soft landing rockets are ignited when the Soyuz capsule is about 1 meter from the ground and they work only a fraction of the second, reducing speed from 7-8 m/s to 0.

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They always fire off only a couple of feet from the ground.

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    $\begingroup$ Maybe so, but do you have any references for this? Statements, documentation, previous touchdown commentary, or something of that nature would be nice. How much velocity do they kill off in those feet? $\endgroup$
    – Caleb
    Commented Apr 10, 2017 at 16:06
  • $\begingroup$ @Caleb It is so. The commentary on NASATV was really not accurate. You can check all the other landing on youtube, and you can see that the retro-rocket are fired for much less than a second. $\endgroup$
    – Giacomo Catenazzi
    Commented Apr 10, 2017 at 16:08
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    $\begingroup$ @Giacomo I believe you guys, but this answer answer could use some fleshing out. $\endgroup$
    – Caleb
    Commented Apr 10, 2017 at 16:13
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    $\begingroup$ @GiacomoCatenazzi It's not about whether the statement is correct (it is), it's about providing more detail and possibly references to back that up. "It is so" is not considered to be a reference, except if you're a well-known authority in a field. So what Caleb is asking is to have the statement "They always fire off only a couple of feet from the ground." backed up with some more details to turn a sub-par answer into a good answer. His comment was meant to help Andyj improve. $\endgroup$
    – DarkDust
    Commented Apr 10, 2017 at 18:36
  • $\begingroup$ @DarkDust: yes, but I refereed to youtube. The problem on giving references on such topic, it that there is much "wikipedia" effect, i.e. one wrong information is copied many and many times. I saw so many conflicting information about spacecraft, that I trust not so much space articles (and if commentator on NasaTV get it also wrong,.. no hope). ESA channel on youtube has good information (from astronauts) on landing sequence). $\endgroup$
    – Giacomo Catenazzi
    Commented Apr 11, 2017 at 7:16

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