Re: So...
Elsewhere, probably in some tweets or PR materials, it's been said that this is some type of cover that goes in/around/over the engines after MECO to help protect them from atmospheric forces during re-entry.
They never mention it during the live streams, and it can be hard to find any credible information on it. It's a regular event seen during main booster reentry, and due to the speed of the booster + relative speed of the object it pretty much has to come from the booster itself. Others may have just guesstimated what it is based on that, that may be where I heard it from too. Must be some proprietary technology for Space X to be so hush about it. UFO is correct here!
Biting the hand that feeds IT
