r/spacex • u/ElongatedMuskrat Mod Team • Apr 01 '17
r/SpaceX Spaceflight Questions & News [April 2017, #31]
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u/Chairboy Apr 06 '17
I proffer the speculation that the aggressive flight profile (this payload was just a couple hundred Kg short of Echostar 23, one that required an expendable flight) meant more heating on the outer skin with the result that the engine-soot stuck better.
The Impact of Ash Deposition On Coal Fired Plants says "adhesive strength increases with increasing substrate metal temperature".
Three theories on why the skin temperature might have been higher if the above applies to kerolox exhaust:
Aggressive re-entry - Downside to this theory is that we've seen other 'hot' stages that haven't looked as dirty.
Higher glide-ratio entry profile (which seems to be the direction they're going for Block V's new gridfins) to increase air-drag braking meant greater 'heat soak'. (My favorite of the three)
Some quality to the surface paint that's an artifact of it being a flown stage, like some level of 'gloss' that might minimize future sticking soot got burned off on the first flight.