Just catching up on the Jan 19th launch of NROL-71 on board the Delta IV Heavy and I noticed these very prominent features in the exhaust plumes, beginning around the time the centre core is throttled down at about T+45s (26:45 in this footage) and continuing for around 15 seconds.

I'm used to seeing some small flashes in the plumes that I assume are due to mixture ratio and combustion inconsistencies; is this the case here? Is it related to the throttling to partial-thrust mode of the core booster?

These seemed especially large and noticeable, but perhaps I just haven't been very observant in the past:

enter image description here

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    $\begingroup$ The RS-68A engine uses an ablative liner in the nozzle for cooling; my guess is that the yellow flashes are (carbon-rich?) bits of the ablative coming out. $\endgroup$ Jan 20 '19 at 19:04
  • $\begingroup$ @RussellBorogove Yeah good call - maybe the timing with the throttle-down is a coincidence and it's actually just when the ablative reaches a critical temperature... $\endgroup$
    – Jack
    Jan 20 '19 at 19:16

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