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This answer says:

The ISS live feed uses the cameras of the HDEV experiment. This is a group of four cameras in a pressurized housing attached to the outside of the ISS.

A hermetically sealed atmosphere is one possibility, but there are several problems with that strategy. Leaks can happen, and outgassing from structural materials and the electronics themselves can raise the pressure (only slightly I suppose) and possibly built up contaminants on the surface of the optics causing scattered light when hit by strong illumination (e.g. sunlight).

Another strategy might be a very slow, controlled leak to space, compensated by a very slow make-up air line from a supply line from the ISS, or from an attached bottle of nitrogen.

Yet another would be to exchange atmosphere with the rest of the ISS via small tubes.

How is this actually done? Was it necessary to address outgassing?

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The cameras are just in a pressurized, "factory-sealed" box.

The encoder, cameras, and other electronics are enclosed in a box pressurized to approximately one atmosphere, containing dry nitrogen, to provide a level of protection to the electronics from the space environment.

Source

The pressurized box is mounted on the Columbus module External Payload Facility (EPF) via a Flight Releaseable Attachment Mechanism (FRAM). It was mounted solely using robotics with no EVA involvement. The only services provided to EPF payloads are electrical power and data which pass through the interfaces on the FRAM. There is no provision for replenishment or any other "management" of payload pressurization gas.

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  • $\begingroup$ As long as the housing contains nitrogen at a pressure of about 1 bar, outgassing will be no problem for all what is in the case. $\endgroup$ – Uwe Mar 1 at 15:45
  • $\begingroup$ @Uwe my question asks how the nitrogen gets there and is maintained. How is it managed. Outgassing is a function of partial pressure of the outgassed materials. Depending on volatility, they can migrate over time. Absolute pressure of N2 only decreases their migration rate, it's not a problem solver and it does not block outgassing, only makes it less mobile. See your own answer to Why are some reaction wheels sealed with low pressure gas, others with vacuum? $\endgroup$ – uhoh Mar 1 at 16:14
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    $\begingroup$ @uhoh You may not like the answer, but that doesn't make it incorrect. It's a sealed box pressurized with dry nitrogen. Nothing more. It is not "managed" in any fashion. If it leaks, the electronics inside will likely eventually fail. Big whoop -- it's just a payload, not Crit I hardware. If outgassing fouls the optics, big whoop -- it's just a payload, not Crit I hardware. $\endgroup$ – Tristan Mar 1 at 17:01
  • $\begingroup$ @Tristan that's saying much more than "pressurized box"; the extra explanation in your comment makes it a clear answer to my question. Example of what I mean, "pressurized suit" and "pressurized cabin" have carefully managed atmospheres, so just saying something is "pressurized" is ambiguous. $\endgroup$ – uhoh Mar 1 at 17:06
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    $\begingroup$ forgive me, I added a bit to the first sentence. $\endgroup$ – uhoh Mar 2 at 6:53

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