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