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enter image description here

For me it looks like water droplets, but I doubt that's the case in space. Also, I don't understand why this should be a craft's surface feature. Wouldn't one aim to design a spacecraft to be as smooth as possible? And even if this is intentionally designed part of the surface, what is this irregularly placed rough stuff intended for?

If it is some environmental phenomenon, what is it and how did it get there?

Here is a contrast-enhanced detail of the Service Module (click on the photo to see the full image):
Apparent bubbling on parts of the Service Module's aluminium skin

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    $\begingroup$ @wheeler: Thats true, but remember we are talking here about the apollo mission. And this is as far as I can tell the orbiter, which was part of reentry(?), in which case the surface would have mattered again. But even if this whole part was covered while leaving atmosphere and not part of the manned reentry section, the question remains as it had a reason why designed this inperiodic and rough way. $\endgroup$
    – Zaibis
    Aug 2, 2016 at 10:53
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    $\begingroup$ we're looking at the Service Module which didn't reenter. $\endgroup$
    – Hobbes
    Aug 2, 2016 at 11:28
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    $\begingroup$ Note that this might not be the external surface - the SIM bay cover was ejected several days before so Worden could use the cameras, etc. Those bumps might be on the stuff below, which could be insulation of some sort. (I've been looking for detailed pics of the bay pre-flight, just before closing it up but can't find any close enough.) $\endgroup$
    – Andy
    Aug 2, 2016 at 12:23
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    $\begingroup$ It is the external skin, above the SIM bay, as seen in this slightly less blurry photo: spaceflight.nasa.gov/gallery/images/apollo/apollo17/hires/… $\endgroup$
    – Leorex
    Aug 2, 2016 at 13:28
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    $\begingroup$ I've replaced the added image with a better view of the area of interest (AS17-145-22252) $\endgroup$
    – Leorex
    Aug 2, 2016 at 19:08

2 Answers 2

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The Apollo Service module was painted with an aluminum paint. Aluminum paint will bubble severely if exposed to temperatures above 747 K, if properly cured. One can only assume the paint was exposed to something close to that temperature at some point in it's lifecycle.

Tracing back, let's see where we can find them. Here's a picture of the SM from the LM after release around the Moon. It's hard to see, but I think I see some evidence of the bubbling near the CM, where there's high glare. This matches the same spot as seen at your image.

enter image description here

The breakdown of the spacecraft is as follows. Note that the image was almost certainly taken from the side hatch.

enter image description here

If I had to venture a guess, I would say it probably happend when the tower was jettisoned, some small flame reached the paint that caused to to boil somewhat.

The next image is at the Rendezvous, post-Lunar mission. There is certainly bubbling seen there.

enter image description here

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  • $\begingroup$ Is there any guess on why exactly that part could have been that close to the temperature, and why expecially the area seems to bea square shaped? $\endgroup$
    – Zaibis
    Aug 3, 2016 at 12:39
  • $\begingroup$ I've been searching, but haven't found anything. It seems it was unique to Apollo 17, and if there was a review on it, I can't find it. $\endgroup$
    – PearsonArtPhoto ♦
    Aug 3, 2016 at 13:16
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    $\begingroup$ @Zaibis The square shape is just the shape of the panel. If you look closely you can see some amount of bubbling around the panel as well. It is not perfectly uniform. As to why that panel was exposed more than the rest of the surface, I'm not sure. $\endgroup$
    – called2voyage ♦
    Aug 3, 2016 at 14:15
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Those are bubbles of air, trapped underneath the reflective mylar sheeting that makes up the outermost layer of heat shield for the forward sufaces of the CM. After splashdown, that's the same material that appears ragged, having been shredded by reentry.

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    $\begingroup$ Citation or further explanation would be helpful. Were the bubbles there prior to launch? If not, where did the air come from? $\endgroup$
    – Russell Borogove
    Aug 26, 2017 at 1:33
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    $\begingroup$ The SM does not survive re-entry, and the CM does not show this bubbling in the photos. $\endgroup$
    – IconDaemon
    Feb 26, 2018 at 13:04

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