During the re-entry of Stage 1 of CRS-11 at around T+6:02 (58.9km up), an object can be seen enter the camera view in the lower left, and pass the camera a second later (58.0km up). (Images below)

At first I assumed it to be a bird, but they don't fly this high. The object seemed to be traveling roughly in the direction of the Falcon 9, suggesting it was not space debri in orbit. Was this object something that was detached earlier in the launch, or did it break off from the rocket itself? What was it?

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    $\begingroup$ Spacebirds? I heard they really like Falcon 9's $\endgroup$ Jun 4 '17 at 3:01
  • $\begingroup$ Possibly this kind of thing? space.stackexchange.com/a/20275/12102 For CRS10 the first stage altitude wasn't displayed on the screen, but from FlightClub the altitude could be estimated to be in the ~50 km ballpark, similar to here. However, the question of what is it? was not answered there, except for " debris, probably from the bottom of the booster when the entry burn was started" so I'd say this is not a duplicate, and a new answer identifying what these "falcon-shaped debris" objects are is still needed. $\endgroup$
    – uhoh
    Jun 4 '17 at 4:56

This is a patch of ice, coming off the rocket from near the liquid oxygen tank.

The ice builds up there due to that tank's very low temperature. The patch comes off when the rocket has high velocity and experiences rising air density.

Normally such ice is white but here it's gray because it's polluted by engine exhaust during the boostback burn.

See e.g. discussion here: https://www.reddit.com/r/spacex/comments/6f3lyo/spacex_on_twitter_falcon_9_first_stage_has_landed/dif56e4/


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