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
