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There is lots of easily accessed information online detailing in what order different ISS modules were added, and who built them. However, what's more difficult to find, possibly buried under the other stuff, is how exactly the modules are attached. Specifically, I am interested in how they pressurized each module. Were the modules pressurized on the ground, and flown up to the station without being opened until they were attached? Or did they attach them, then fill them with atmosphere from tanks?

I did find this interesting video showing the order all the compartments were added in.

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  • $\begingroup$ They were launched pressurized. l'm confused by what that has to do with how they were attached though, so holding off on posting as an answer. Can you clarify? $\endgroup$
    – Organic Marble
    Commented Jul 23, 2016 at 10:24
  • $\begingroup$ Basically I want to know what the attachment procedure was like. Are there doors between the compartments that were kept shut until it was attached? If they were pre-pressurized, can the compartments be sealed off in case of a breach? $\endgroup$
    – Phiteros
    Commented Jul 23, 2016 at 21:37
  • $\begingroup$ OK, I'll write up an answer for you, focusing on the pressurization steps. I thought you might want to know all the mechanical attachment stuff, but I think that's been covered here already. $\endgroup$
    – Organic Marble
    Commented Jul 23, 2016 at 21:49
  • $\begingroup$ Sounds good, thanks. I did a search and didn't find any Q&A on here that had what I wanted. $\endgroup$
    – Phiteros
    Commented Jul 23, 2016 at 21:50

1 Answer 1

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The ISS modules were launched pressurized, if for no other reason than that to pressurize them in orbit would be a drain on ISS resources.

The mechanical interface between a new module and the ISS is the Common Berthing Mechanism (CBM), which has been discussed on this site quite a bit. This answer will focus on the process of opening a pressurized path from the ISS to the new module.

The CBM forms a ring around the hatch, shown here.

enter image description here

Of interest to this answer is the Manual Pressure Equalization Valve towards the bottom of the hatch.

Our working example will be the Japanese Experiment Module (JEM), carried up on STS-124. I couldn't find a photo of the CBM end of the module so here is a graphics rendering of it. The red A labels the hatch/CBM on the JEM and the red B labels the hatch/CBM on the ISS where the module will be attached.

enter image description here

Once the robotics/CBM magic happens and the JEM is mechanically installed, a "vestibule" has been created. I couldn't find a good schematic of this so I drew up a terrible one. This tries to show a view looking perpendicular to the long axis of the JEM

enter image description here

This vestibule is formed by the rings of the CBM and the hatches on either side. Once the module mating is complete, the vestibule is at vacuum and the ISS and new module are at normal pressure.

NASA has chosen to not publish any Assembly Ops Checklists on the web but Spaceref.com once did (now gone), for the US Lab. The procedure is called VESTIBULE PRESSURIZATION AND LEAK CHECK and starts on document page 121. In brief, it describes how, on the ISS side, a crewperson will open the MPEV and allow air to flow into the vestibule from the ISS. Once a period of time has elapsed, or the flow stops, the MPEV is then closed, and time is allowed to elapse to ensure that the vestibule does not have a leak.

Once everyone is happy that there is not a leak, the MPEV is re-opened, and the ISS hatch is opened. The MPEV on the new module is then opened, and once equalization is complete, the module hatch is opened.

The module can now be accessed and outfitting can begin.

Here's an excerpt of the procedure:

enter image description here

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    $\begingroup$ Quite frankly launching a module in a vacuum would be more difficult than launching it pressurized... $\endgroup$
    – PearsonArtPhoto ♦
    Commented Jul 23, 2016 at 23:32
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    $\begingroup$ Absolutely! It would have to be absurdly strong (ie heavy) in the crush direction. And launching one pressurized, then letting it vent down, would just be ridiculous. $\endgroup$
    – Organic Marble
    Commented Jul 23, 2016 at 23:39
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    $\begingroup$ Was the bigelow module pressurised in transit? $\endgroup$
    – user20636
    Commented Apr 12, 2018 at 5:52

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