I have read that some unmanned craft, like the Corona spy satellites and some early moon missions, used film instead of just a video camera to send us back their images. Even if they werent coming back.

Does anyone knows why and how the film was used for that purpose:

Thanks.

The Corona satellites used return capsules to return the film to earth. Lunar Orbiter, to make high resolution images of future Apollo landing sites, used a camera with film that was developed and scanned on-board, like on the early soviet lunar probes. In those early days, electronic camera tubes were nowhere near the quality neccessary to produce the required resolution, thus they had to revert either to returning the film or scanning developed film, which could be done at much higher resolution and quality.

Harald

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"Flying in space is risky business, but just staying on this planet is risky business too." - John Young, astronaut

The Estar film base used by the Apollo astronauts was developed for Project Corona.

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"Facts are stubborn things." --John Adams
Clavius Moon Base

What method did they use to scan the developed film to produce an electronic image?

Perhaps a flying-spot system?

Yes - see http://www.vgl.org/webfiles/mike/lo-cam.htm

A 6.5-micron spot was used. Come to think of it, either flying spot or moving-emulsion systems were about the scanning choices until first TV detectors, then linear arrays, and finally 2D digital systems came along. It took forever to scan a big Palomar or KPNO plate with one of those spot systems... but it preserved an enormous amount of information.