Construction of ISS modules

[Saturn1234]

I have a question about module walls on the ISS. I know they are about 10cm thick. It's two layers of aluminum with a gap in between to act as a whipple shield. Are those walls just to "keep air inside" and "act as a shield against MMOD" or are they "crammed with electronics"? Are there, for example, tubes with coolant, sensors, distribution lines and so on?

[Jim]

I have a question about module walls on the ISS. I know they are about 10cm thick. It's two layers of aluminum with a gap in between to act as a whipple shield. Are those walls just to "keep air inside" and "act as a shield against MMOD" or are they "crammed with electronics"? Are there, for example, tubes with coolant, sensors, distribution lines and so on?

No, the MMOD shield is just panels placed on the exterior of the module hull.   There isn't anything "stored" between them.

[Saturn1234]

No, the MMOD shield is just panels placed on the exterior of the module hull.   There isn't anything "stored" between them.

And is there something on the inside of the pressure vessel?

Why is the inside of the module grey-green?

[zubenelgenubi: Attach files, including images.  Do not embed them.]

[zubenelgenubi]

Why is the inside of the module grey-green?

Experts, please correct me if I am wrong.
It's primer.

[cohberg]

Experts, please correct me if I am wrong.
It's primer.

Yes, its an anti corrosion primer per Don Pettit

Per me, the non expert: I believe that the relevant standard describing the coating is MIL-DTL-5541.

This specification covers chemical conversion coatings formed by the reaction of chemical conversion materials with the surfaces of aluminum and aluminum alloys
...
coatings...[can be] iridescent yellow, brown

Specifically Type I, Class 1A

Type I – Compositions containing hexavalent chromium [coating has color]

Class 1A chemical conversion coatings are intended to provide corrosion prevention on unpainted items as well as improve adhesion of paint finish systems on aluminum and aluminum alloys. Coatings of this type may be used, for example, on tanks, tubing, and component structures where paint finishes are not required for interior surfaces but are required for the exterior surfaces.

[Jim]

And is there something on the inside of the pressure vessel?

Everything is inside of the pressure shell.  Especially, since it is not on the outside.

Don't understand what you are looking for.

Is it that fact that there are four of those standoffs 90 degrees apart that have all the utilities plumbed through them.  The racks then attach to the standoffs.

[cohberg]

And is there something on the inside of the pressure vessel?

Because I too had trouble visualizing the interior layout a long time ago, here are some visualizations along with Jim's notes.

Everything is inside of the pressure shell.  Especially, since it is not on the outside.

Everything outside of the pressure vessel (the inner most layer of the module) is in vacuum



From top to bottom we have (with some variation on order depending on the module):

Vacuum of space
Whipple shield
Insulation
Kevlar to catch fragments from the Whipple shield impacts
Pressure Vessel
Atmosphere with people and things

On the image below you can see the outside is the Whipple sheild, the MLI and Kevlar layer, then finally the pressure vessel with the orthogrid.

Is it that fact that there are four of those standoffs 90 degrees apart that have all the utilities plumbed through them.  The racks then attach to the standoffs.

Here is Columbus without the racks. You can see the standoff that Jim is describing with the ECLSS / utility plumbing.
Everything you see is on the inside of the pressure vessel.

[Hobbes-22]

On the image below you can see the outside is the Whipple sheild, the MLI and Kevlar layer, then finally the pressure vessel with the orthogrid.

The image shows the pressure vessel using the label 'primary structure'.

[catdlr]

The Insane Engineering of the ISS

Dec 6, 2025

Credits:
Producer/Writer/Narrator: Brian McManus
Head of Production: Mike Ridolfi
Editor: Dylan Hennessy
Writer/Research: Josi Gold
Animator: Eli Prenten
Animator: Stijn Orlans
Sound and Production Coordinator: Graham Haerther
Sound: Donovan Bullen
Thumbnail: Simon Buckmaster
Head of Moral: Shia LeWoof

References:

Select imagery/video supplied by Getty Images
Thank you to AP Archive for access to their archival footage.

[StraumliBlight]