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enter image description herePhoto: ESA

In this answer to How (the heck) do you replace a space station window in orbit? it is explained that cupola windows can be completely replaced in orbit. Unfortunately, one of the .pdf has been lost to link rot.

The inner “scratch pane” has already been replaced on the large circular window, but this is relatively easy since it is the innermost pane. If the entire window needs to be replaced, a pressure cover (launched on request) is installed during EVA to maintain pressure integrity of the cupola while the window is replaced from inside. (See the photo below for the location of fasteners and internal retainer frame.)

This would be a much more complicated process than replacing a scratch pane. The pressure hatch would be subjected to several tons of pressure once pressure is equalized across the panes. The exterior surface of the cupola does not look like provision has been made for hatch dogs or a sealing interface.

Provision for pressure equalization would be needed if the window is still air-tight. The replacement procedure would need to be altered if one or more panes had been violated. Even a small leak could potentially interfere with installation of the pressure hatch. The windows appear to have an area of about 3 square feet so even 0.25psi would generate 100 lbf which would be difficult for an EVA astronaut to overcome.

I’m sure the folks at ESA have planned for all contingencies. Is there documentation available on the pressure hatch design and procedure decision tree?

Edit: detail from @lobbymcblobby’s answer shows what are presumably a row of bolts around the periphery of the external pressure cover frame for installation. As @Darth Pseudonym points out, the attachment area would be covered by what appears to be an insulation blanket enter image description here

enter image description here

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  • $\begingroup$ The exterior may have more equipment than you'd think, but it's hidden under the insulation blanket unless it's actively in use. Removing the insulation is probably part of the cover installation procedure. $\endgroup$ Commented Jan 29 at 17:20

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So not really an answer, so hesitant to post, just only partial as I haven't found the actual info the OP is looking for:

enter image description here

enter image description here

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(what is (partially) labelled Window Fix Captive Bolts - presumably once the external pressure cover is fitted (to the main structure) then these are unscrewed to remove the entire pane)

enter image description here

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(Note pull tabs on insulation to access, presumably, bolt holes for attaching external pressure covers)

enter image description here

(Although this is the STA, the holes shown might be where the external pressure covers attach to the frame)

But, in the meantime there is the following, whilst not changing the answers in the other questions, does add an interesting infographic Window Assembly Components (even if it is just for the US Lab) :

https://www.cbsnews.com/network/news/space/srh/SRH_130.pdf

Had this bit of extra info:

Cupola’s internal layout is dominated by ... “close-out” panels, which cover the harness and water lines attached to the Cupola. These internal panels form a pressurized air distribution system with the outer structure. These panels are removable to allow inspection and connection of different utilities.

enter image description here

(Flex hose on Cupola windows)

https://www.nasa.gov/wp-content/uploads/2018/04/iss-operating_an_outpost-tagged.pdf

has this:

internal and external pressure cover info

Note: Internal Pressure Cover and External Pressure Cover are not nominally installed. Internal Pressure Cover is installed in the event of pane failure or pane seal leak. External Pressure Cover is installed when replacing a window pane.

and says:

The windows of the US hatches, US Laboratory, JEM, and Cupola are designed to be replaceable in the event a window pane breaks. An astronaut would install an external pressure cover over the window, via an EVA, to replace the windows exposed to space.

The window would then be removed from the inside of the ISS. The windows themselves cannot be removed by a spacewalking astronaut; the removal must be done from the pressurized environment of the ISS cabin.

Thus, if debris were to damage both panes of a window and cause a module to depressurize, it would not be possible to replace that damaged window.

Instead, the crew would install the external pressure cover, via EVA, and repressurize the evacuated module.

The crew could then go into that module and remove the window.

With the window removed, the crew would install an internal pressure cover over the window’s hole until the new window was ready to be installed.

The pressure covers are on orbit to provide a means to respond to a broken window pane; however, no spare windows are kept on board the ISS. A spare would need to be manufactured and flown after the failure.

In basic terms it looks like a cover that has to be bolted on from outside (with the window shutter set aside).

And a matching cover to bolt on the inside (as the pane replacement in its entirety), with a flex hose attachment.

Apparently 2 covers are on orbit.

But unable to find any other diagrams, tables or data.

(extra pictures extracted from Philippe Deloo 2009 Presentation, ISS infrastructure division)

Thanks to Organic Marble, this link https://www.ibiblio.org/apollo/Shuttle/EVA%20Checklist/STS-130%20EVA%20Checklist.pdf to the STS-130 EVA checklist, which is the flight that brought the Cupola to the ISS. On page 356 the external pressure covers are portrayed in a detailed line drawing attached to the Cupola (check comments below):

illustration of external pressure covers attached to cupola

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    $\begingroup$ Unsourced speculation, but the 'pressure on partially fitted cover' of concern in the Q could be avoided by fitting inner cover first, waiting till damaged window panel bleeds down, fit outer cover, repressurise and remove inner cover to do repair. Just then need a mechanism to bleed down volume between outer cover and outer glass to allow safe removal from outside. $\endgroup$ Commented Jan 27 at 12:01
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    $\begingroup$ Interesting, that says they do have the covers on-orbit. But maybe not for all window types. $\endgroup$ Commented Jan 27 at 12:03
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    $\begingroup$ Just FYI, there are some schematics on and around page 256 of the STS-130 EVA checklist (the flight that brought up the cupola). They are excerpted from some other document and the labels are not explained, but on p. 256 it looks like the external covers are installed. ibiblio.org/apollo/Shuttle/EVA%20Checklist/… $\endgroup$ Commented Jan 30 at 2:36
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    $\begingroup$ I shan't be writing an answer on this one. If the schematic is useful to your answer, please utilize it. If I find the source document, I will report back. $\endgroup$ Commented Jan 30 at 12:59
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    $\begingroup$ I ran into the same error on askubuntu. There's a meta topic about it, seems systemwide. $\endgroup$ Commented Jan 30 at 20:34

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