Just after T+3 minutes during today's SES-11 launch I noticed a small chunk fall off the end of a "boom" on the Falcon 9 second stage.

Video frames

What's the boom and what came off? Just a chunk of ice?


2 Answers 2


It's hard to say for sure, but here's what I suspect happened:

The small boom was the deployment of the grid fins. It happened within a few seconds, and it's not uncommon for audio to be off for such items. Note there was a small amount of applause right after that boom, indicating it was something expected.

The chunk was certainly something small and inconsequential. It can be seen that it comes from some kind of a small pipe near the bell. I believe it is the Nozzle Fuel Return Line, seen in the below diagram. It could also be a feed line that takes the fuel and pre-warms it before entering the ignition chamber.

enter image description here

In any case, it is almost certainly a small chunk of ice. It seems to completely disappear when it enters the exhaust, likely sublimating completely.

  • 1
    $\begingroup$ It looks more like that tube on the other side of the nozzle from the fuel return line in the left image. It appears to be a purge or drain line. $\endgroup$ Commented Oct 12, 2017 at 11:55
  • $\begingroup$ Yeah, could well be. That line isn't marked, so it's a bit tricky to know for sure... $\endgroup$
    – PearsonArtPhoto
    Commented Oct 12, 2017 at 12:37
  • $\begingroup$ Sorry, by "boom" I didn't mean a sound, but rather the pipe or whatever that's protruding, from which the chunk detached. Here's a cleaner contrast image of it from T+9:32 when the engine isn't firing. I think @OrganicMarble is correct and it's the pipe at the bottom of the TCA. Something similar happened at T+2:52. How often is purge used and is it possible it gets buildup at the outlet that freezes? In any case good to know it's inconsequential, and thanks for that awesome diagram by the way! $\endgroup$
    – rkagerer
    Commented Oct 19, 2017 at 6:11

Looks to me that it is the combustion by-product of LOX and RP which produces CO2 and H2O. The H2O freezes in the cold environment of space. The pipe appears to be the exhaust of the gas generator.


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