Generally the CBM ports were meant to connect new space station nodes together.

The nadir port on Harmony (Node 2) has been used for more berthings than any other that I am aware of.

As of Jan 2014, it has supported:

  • 4 HTV berthings (plus one swap of the HTV from nadir to zenith to make room for a space shuttle docking) for a total of 5.
  • 3 Dragon berthings (#4 due in Feb 2014)
  • 2 Cygnus berthings

For a total of ten berthing events to date of writing this question, with 16 more expected at a minimum (duration of Orbital (8 flight) and SpaceX's (12 flights) current contracts with NASA).

What is the operational lifetime, in units of berthing events for a CBM port on an ISS module?

Contrast with the aft port of Zvezda which has supported dozens of docking operations, but is of a very different design. Or the forward port on Mir. Or aft port on Kvant which was attached to the aft port of Mir).

  • $\begingroup$ The Pressurized Mating Adapters (PMAs) that were used to dock the Shuttle to the ISS were used a lot more than have the CBMs. $\endgroup$ Commented Mar 19, 2014 at 5:56
  • $\begingroup$ @DavidHammen I read the Wikis on CBM and PMA as well as my Ref Guide to the ISS and I'm still confused. Isn't the CBM a component of the PMA? Are the Dragons et al berthing without a PMA, or is this what geoffc means to ask about? $\endgroup$ Commented Mar 20, 2014 at 2:11
  • $\begingroup$ @JerardPuckett The CBM, is how the modules connect to each other, widest opening. To connect the Russian segments Zarya to Unity the CBM on aft end of Unity has a PMA, whose other end plugs into Zarya. On the forward end of Harmony there is a CBM with a PMA attached for Shuttle docking (and future DragonRider/CST100/DreamChaser). Dragon, Cygnus, and HTV use the earth facing CBM on Harmony right now. $\endgroup$
    – geoffc
    Commented Mar 20, 2014 at 2:57

1 Answer 1


ESA has a doc about the design of the docking ports (IDS - Internation Docking Standard, sometimes also called NDS NASA Docking System, sometimes called LIDS - Low Impact Docking System. Though technically LIDS became NDS which fulfills the IDS standard).

On page 3 it says for the IDS ports, design goal is 30 cycles.

For the CBM ports, a NASA Tech Doc says:

The 5/8-inch-diameter bolt with .625-18 UNJF rolled thread is made of Inconel 718 (AMS 5664) and coated with a dry film lubricant to help prevent galling during the nearly 400 engage/disengage cycles required.

So 30 for the IDS, which Dragon is bringing to the station on Spx-7, and again on Spx-8 (since they will be moving PMA-3 to the Node 2 Zenith, to allow 2 docking ports, and freeing up Node 1 Nadir for the second CBM port).

400 for the CBM interfaces.

This makes sense as the IDS seems to be replaceable, given that it is being 'delivered' so when it gets near end of life, deliver a new one to replace it. Whereas the CBM ports are pretty much built into the modules, so 400 is a better number.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.