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The Teslarati article SpaceX Falcon 9 Block 5 rocket’s drone ship return captured in stunning detail [gallery] and accompanying photo spread shows many interesting details of "SpaceX’s first West Coast Falcon 9 Block 5 booster recovery in the best detail yet seen of the rocket upgrade, well-worn after its first successful launch of Iridium NEXT-7, July 25."

Of particular note are detailed views of the silky black “highly flame-resistant felt” now covering Falcon 9’s interstage (the top segment), landing legs, octaweb section, and raceways (the black lines traveling up and down the rocket). Compared to beat-up, older Falcon 9s, B1048’s shielded components look barely worse for wear, and it would genuinely be difficult to determine if the rocket had flown before without the telltale soot fingerprint present after every Falcon 9 recovery.

Question: What is the nature of "the silky black 'highly flame-resistant felt'" on Block 5 Falcon 9's and what is its intended function(s)? What are all of the locations where is it applied? Also, could you point out exactly where is it seen in these photos?

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  • $\begingroup$ @geoffc you usually eat this kind of question for breakfast! Any thoughts? $\endgroup$ – uhoh Aug 30 '18 at 23:59
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This came into Falcon 9 design with Block 5 improvements. As Elon Musk mentioned in updates about Falcon 9 Block 5 it is carbon fiber hydrophobic thermal protection developed at SpaceX. The reasons why they replaced are pretty obvious. One reason is the heat factor and the other reason is expenses.

The problem with heat occurs during stage separation and descend. Sometimes during stage separation engine of the second stage damage the inner stage. Another reason is just repainting expanses. During entry burn and landing burn a lot of the exhaust from the engine stick to the booster(that is the reason why the parts of the rocket hidden under the legs are white, other parts are not. Picture). As a result, the whole rocket had to be cleaned/repainted. SpaceX avoided this by having interstage to be completely black. The question of why the whole rocket is not black then has a simple answer. Black is a good heat-absorbing color. The fuel that SpaceX uses is liquid oxygen that has to be kept at very low temperatures, as a result, they cannot have the whole rocket be black. But the interstate does not contain anything heat-sensitive.

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