Spacex's Dragon and JAXA's HTV are currently the only vehicles that can bring unpressurized cargo in addition to the pressurized one inside the vehicle.

In the odd event that the ISS urgently needs more in-station cargo than can be carried inside the pressurized modules of the dragon or HTV, could we send part of it as unpressurized cargo, and it would then be secured through an airlock with the help of a robotic arm or an EVA?

Are things on the External Stowage Platforms ever taken inside?

How often are things from inside the station taken outside? (maybe like hand-deployed satellites? Please do not include EVA suits themselves in answers to this question)

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    $\begingroup$ Would the Bigalow Expandable Activity Module, delivered to the ISS as unpressurised cargo on CRS-8 by Dragon count? It was removed from the unpressurised cargo trunk, and attached to the ISS on a port, before being expanded, pressurised and is currently used for storage. $\endgroup$
    – Moo
    Jun 2, 2020 at 11:41
  • $\begingroup$ Thank you @Moo I did not know about BEAM. It doesn't count since it was berthed like other vessels and modules. The question is more about using the airlocks specifically. Technically every ISS module was initially in an unpressurized cargo bay or trunk, and then got berthed to the main structure (sometimes permanently). $\endgroup$ Jun 2, 2020 at 12:42

1 Answer 1


The Robotic External Leak Locators (RELL), which are mounted to the Special Purpose Dextrous Manipulator (SPDM) and then moved by the Space Station Remote Manipulator System, are stored inside. So if they need to be used, the crew must go EVA to mount them on the SPDM and then return them inside when the task is complete.

A "RELL garage" has been built and will be mounted externally on the ISS to keep the crew from having to do an EVA when the leak detection task needs to be done.

It's not uncommon for failed equipment to be brought inside at the end of an EVA and worked on or prepared to ship to the ground. One example is the Main Bus Switching Unit and Battery Charge/Discharge Unit mentioned here on 12/26/2019.

So the types of operations you mention are certainly possible.

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    $\begingroup$ The question asks about the unpressurized cargo in the trunk area. Was it ever sent and secured by ISS through RELL or directly through EVA? Your answer mentions that this could be done. Has it ever been done? $\endgroup$ Jun 1, 2020 at 16:52
  • $\begingroup$ @ChandanSinha the question asks many things. I have addressed some of them like "how often are things taken outside" $\endgroup$ Jun 1, 2020 at 16:58

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