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The Lunar Orbiter program was very successful in mapping the surface of the Moon. Images were taken on a 70 mm film, developed in a semidry process, and then scanned by a photomultiplier for transmission to Earth. But how to develop a film in zero gravity? Semidry is not without any liquids, but liquids are difficult to handle in zero gravity.

The semidry process was used before in classified reconnaissance satellites, may be some details are still classified.

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    $\begingroup$ In free fall, liquid behavior is dominated by surface tension -- a dampened sponge, cloth, or wick can deliver liquids to a surface moving against it with no dripping or spilling, which seems like it could actually be an advantage. $\endgroup$ – Russell Borogove Sep 13 '18 at 19:54
  • $\begingroup$ @Russell Borogove "a dampened sponge, cloth, or wick" may be very helpful in zero gravity, but it should be kept dry during launch and any acceleration. The liquid developer could be within a bladder and is released to the sponge, cloth, or wick. But there should be a method for replacing used developer with fresh developer. $\endgroup$ – Uwe Sep 13 '18 at 20:02
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    $\begingroup$ Expert tip - developer stinks, so remember to leave a window open while you're using it. $\endgroup$ – Don Branson Sep 13 '18 at 20:19
  • $\begingroup$ Unless you’re in space. $\endgroup$ – Russell Borogove Sep 13 '18 at 20:23
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    $\begingroup$ @Uwe - it's been a long time for me. I couldn't remember for sure which it was. $\endgroup$ – Don Branson Sep 13 '18 at 21:40
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It appears that the Eastman Kodak "Bimat" system used on the Lunar Orbiters was completely dry - in the sense that there were no free liquids.

You can read about the process in detail at the Central Intelligence Agency's library website in this document. The pdf format used does not allow copying text, so here is an brief excerpt.

No free liquids are required at the time of processing negative films. Liquids cannot be squeezed or shaken from the BIMAT Transfer Film. Thus, the solution containment problem is completely eliminated from photographic processing. This is important in airborne processors and those operating in a space environment...

There is a good schematic of the system, here, on page 250.

enter image description here

You can see how the "Transfer Film", soaked in the "imbibant", is pressed against the film by a roller called the Processor Drum "for a suitable length of time." The developed film then passes by a dryer and on to the film scanner.

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    $\begingroup$ Early "space darkrooms" and "space faxes" are amazing! I've just asked Better source for the 1967 photograph of Surveyor-1 by Lunar Orbiter-3? $\endgroup$ – uhoh Sep 14 '18 at 1:40
  • $\begingroup$ I see no transfer film in the schematic, I only see a web supply and take-up. The web seems to be soaked with a combined developer and fixer. The web and the film are the only two things going to the processor drum. $\endgroup$ – Uwe Sep 14 '18 at 12:34
  • $\begingroup$ The term "Transfer Film" is from the CIA document. $\endgroup$ – Organic Marble Sep 14 '18 at 12:38

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