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Watching the scrubbed inaugural launch of SLS, there has been plenty of close up views from the vehicle, including a close up of the SSME engine mount, that exhibits those white extruded squares or rectangles, varying in size and shape.

What are these things and what do they contain? If it wasn't NASA, it would look like some mockup designer added decoration to make a spaceship look more sci-fi.

sls engine mount (source: NASA)

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  • $\begingroup$ My first guess would have been "access panels". But what an access panel looks like is in the center of the image. Some of them are probably sensors. And others are probably attachement points for stuff on the inside (strenghtening the thin sheet of metal in the places where stuff is attached). But those are really just guesses (that's why this is no anwer) $\endgroup$
    – TrySCE2AUX
    Aug 30, 2022 at 12:53
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    $\begingroup$ I agree that it's unlikely that these bumps on SLS are decorative. In case anyone is wondering, decorative bumps on a sci-fi spaceship are called "greebles", "greeblies" or "nurnies". $\endgroup$
    – Nimloth
    Aug 30, 2022 at 14:55

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Looking at the full resolution version of this NASA picture

enter image description here

it appears that they are slabs of insulating cork. Especially obvious in this crop from the area just above the red hatch cover (crop and annotation by me). The indicated slab of cork can be seen in the lower left of the red circle in the picture in the question (the red hatch cover is over the bolted access panel).

enter image description here

(picture from question, green arrow added by me)

enter image description here

This article confirms the boattail is covered in cork insulation:

Cork is heavier than foam but provides even stronger protection for certain applications. Cork comes in sheets and is applied to areas that have high predicted heat loads, like the core stage engine section, which houses four RS-25 engines that produce 2 million pounds of thrust.

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    $\begingroup$ This is a great answer thanks, still I find it amazing that those slabs of cork are cut so straight and seem to be glued as they come off of a cookie cutter, with no rounded corners nor beveled edges, when one might think round corners could help prevent rip off, beveled edges help aerodynamics, and allow to fine tune the amount of insulation required in each case, and save grams by the way $\endgroup$
    – jkztd
    Aug 30, 2022 at 18:14
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    $\begingroup$ @qqjkztd I guess they didn't just wrap the whole boattail with a thicker layer of cork for reasons of weight, instead just sticking these squares on over the areas that needed more insulation. Maybe by this point down the stage the whole surface is engulfed in a boundary layer or recirculation so streamlining wouldn't help much. Just guesses though. $\endgroup$
    – Organic Marble
    Aug 30, 2022 at 18:21

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