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Watching video of today's test of Northrop Grumman's OmegA first stage SRB after the test is over and the flames have died down a bit, it looks like they are sticking something into the back end of this rocket to probe it.

Question: What is the device shown in the rocket's nozzle, and what purpose does it serve?

Screenshot from OmegA Milestone: First Stage Static Test Fire

OmegA Rocket First Stage Static Test Fire

OmegA Rocket First Stage Static Test Fire

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    $\begingroup$ Related: what would one learn by borescoping a rocket engine? $\endgroup$
    – Russell Borogove
    Commented May 31, 2019 at 8:05
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    $\begingroup$ LOL, they "borescope" SRBs by lowering a technician down into it on a sling. $\endgroup$
    – Organic Marble
    Commented May 31, 2019 at 21:00
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    $\begingroup$ Is the nozzle supposed to look that damaged? $\endgroup$
    – Moo
    Commented Jun 1, 2019 at 4:14
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    $\begingroup$ Much better... :) Down vote removed. $\endgroup$
    – RonJohn
    Commented Jun 1, 2019 at 11:44
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    $\begingroup$ @Moo no, it suffered a failure late in the test. $\endgroup$
    – Organic Marble
    Commented Jun 1, 2019 at 12:04

2 Answers 2

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It's a quenching probe.

After burnout of the booster was confirmed, a CO2 fire extinguisher was moved into the nozzle area to inject carbon dioxide into the booster to kill any remaining fire in order to preserve the systems in their condition at burnout, allowing for a detailed study of the components of the SRB. 

Source: http://www.spaceflight101.net/sls-srb---qm-1-updates.html

(This is from an article on a Space Launch System SRB test)

Presumably required due to the non-flight-like horizontal attitude at burnout.

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    $\begingroup$ It may be required in order to preserve the engine (as much as possible) for inspection afterwards. $\endgroup$
    – ceejayoz
    Commented May 31, 2019 at 13:09
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    $\begingroup$ @ceejayoz that is indeed the purpose as stated in the quote in my answer. $\endgroup$
    – Organic Marble
    Commented May 31, 2019 at 21:19
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    $\begingroup$ @OrganicMarble I'm pretty sure a comment got deleted somewhere that I was replying to. $\endgroup$
    – ceejayoz
    Commented May 31, 2019 at 21:28
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    $\begingroup$ I'm guessing this is unburnt "ash"? Actual solid fuel contains an oxidiser and would keep burning in a CO2 atmosphere, wouldn't it? $\endgroup$
    – Rich
    Commented Jun 1, 2019 at 3:25
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    $\begingroup$ So they're probing the rocket's action end. For science. $\endgroup$
    – Machavity
    Commented Jun 1, 2019 at 3:28
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Structural failure of the nozzle happens prior to the probe being inserted. Without the nozzle, parts of the tail end of the rocket were burning and were not supposed to be. The fire was then extinguished with the probe to save the rocket itself and to save any evidence of why the nozzle exploded.

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  • $\begingroup$ The probe was used on every test, whether the nozzle was damaged is irrelevant. $\endgroup$
    – Organic Marble
    Commented Jun 7, 2019 at 0:34

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