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In How do phonesats stay cool? I wonder if phonesats might have had "cabin pressure" to keep the phones from overheating since they are not designed for space.

But now I'm just wondering if there are any spacecraft that maintain an atmosphere that are not related to crewed spaceflight, i.e. excluding capsules, space stations and delivery craft bringing stuff to them.

In order to avoid getting closed as a duplicate, please don't write answers based solely on Venera or Sputnik spacecraft because these are already answers to Are fans ever used in un-crewed spacecraft?

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The original spy satellites used film cameras. They were pressurized with a half atmosphere of nitrogen. What’s really interesting is that they didn’t need to be, according to the manufacturer. This predates the Mercury program, so I get the sense this was tacked on to the earliest space program to prepare for “Man in Space”

The interior of the spacecraft was to be pressurized with nitrogen at half an atmosphere, and regulated for temperature and humidity. This was not a reconnaissance requirement and the camera designers had no say in its establishment. The pressurized capsule would maintain a temperature of approximately 70 degrees Fahrenheit (21 degrees Celsius) and a relative humidity of approximately 50 percent. Pressurizing the spacecraft in some ways made the mechanical design of the camera simpler, since its moving parts did not need to operate in a vacuum and thermal control was easier. But it was not necessary for the camera and indeed Itek had designed the CORONA camera to operate in vacuum. Furthermore, the pressurization system added weight, requiring a pressure vessel, the environmental systems, and a window for the camera to look out instead of a hole cut in the side of the vehicle. Ideally, all of this weight could have been better used carrying more film.

https://www.thespacereview.com/article/1419/1

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    $\begingroup$ An atmosphere with a relative humidity of 50 % avoided damages to the film images by static discharge. $\endgroup$ – Uwe Jul 5 at 15:04
  • $\begingroup$ Well, Itek didn’t think so. It’s possible that this was all from an abundance of caution. The troubles in Mercury, Gemini and Apollo were mostly public. Corona and it’s sister program appear to have had far more problems getting to space, but the failures were all classified. I think the Eisenhower Adm. was desperate for a win. $\endgroup$ – Anthony Stevens Jul 5 at 15:22
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    $\begingroup$ The film magazines of the Hasselblad cameras used on the moon were modfied to discharge static electricity without causing light from arcs damaging the images on film. Did they test the camera in a vacuum chamber on Earth without a nitrogen atmosphere? $\endgroup$ – Uwe Jul 5 at 15:33
  • $\begingroup$ This is really interesting, thanks! Not these obviously, but some spacecraft also developed the film and these also may have had atmospheres: How to develop a photographic film in lunar orbit? $\endgroup$ – uhoh Jul 6 at 1:55

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