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In a recent question there's this image of a display in the restored Apollo Mission Operations Control Room 2:

NASA’s restored Apollo Mission Control - Ars Technica

I always wondered, how do these displays work (the original ones from the 60s/70s, not the restored ones)? As far as I know, these aren't static images but they have at least some "animations".

Here's a photo from April 13, 1970 during Apollo 13 showing a world map:

Mission Control during Apollo 13

What strikes me is that these displays seem to be pretty high-resolution, more than I would expect from a raster display controlled by a computer of that era.

(Might be off-topic for Space.SE, but I've only noticed those displays related to NASA so far. And some movies.)

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As Russell Borogove wrote, scribing projector displays were used.

The displayed image was generated with three different types of projectors in parallel. The light from all these projectors was added on the screen. enter image description here

  • One background projector displayed the static slide with the Earth or Moon map.
  • Another projector to display the moving symbol for the spacecraft. The slide was moved horizontally and vertically under numeric computer control to move the spacecraft symbol to the right position on the map.
  • Up to five scribing projectors to display the spacecraft trajectory. An opaque slide was used to scribe the line under computer control by removing some of the opaque material. The scribed image is displayed as it is plotted to the slide and thus to the screen.

The slides with the maps could be changed as neccessary during the several phases of the mission, Earth orbit, transfer trajectory, Moon orbit, transfer back to Earth and reentry to Earth until splash down. There were special maps for abort modes and recovery. But all these maps slides should be prepared before the mission and could not be modified during the mission.

Both the map and the scribing projectors had slide magazines for up to 40 different slides random selectable under computer control.

The slides were made with transparent lines on a black background. Filters in red, green, blue, magenta, yellow and cyan were used with projectors to compose an image with a magenta map, red spacecraft symbol and a yellow trajectory.

Different symbols could be selected for the CSM, CM and LM. enter image description here

These projection displays should not be used in a very dark room like a cinema, the mission control room should be lighted to do paperwork. High power xenon arc lamps were used to get a bright image. The slides should be cooled with forced air from compressors and exhaust pipes were needed to get the heat out of the projector room.

Many thanks to Russell Borogove for giving me the right words "scribing projector display" for the search machine to find the image at arsTECHNICA.

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  • $\begingroup$ Thanks for running with it, I didn't have time. $\endgroup$ – Russell Borogove Jul 1 at 20:52
  • $\begingroup$ In the MCC at Johnson, the projectors are located behind the screens in a large, mostly empty room known as the "bat cave". In the Apollo days the room was pretty large to allow for the focal length of the projector for the middle screen. Different projector technology was used for the Shuttle displays and the room was shortened. The recent restoration of the MCC didn't restore the "bat cave" to its full length, but no one can see that. Much of the equipment to drive the fake displays is located in the "bat cave". $\endgroup$ – Organic Marble Jul 3 at 19:16
  • $\begingroup$ Apollo In Real Time has some footage of what I think is one of these scribe projectors updating traces starting at mission time 102:21:18. $\endgroup$ – Russell Borogove Jul 20 at 19:58
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According to this ars article: The large screen uses the described method to display the spacecraft position, but all other information was displayed via several Eidophors. The large display was also used by the Eidophors. The exact number of these devices is not mentioned. Somehow the linked article is a Google link, but it is very worthwhile to read.

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  • $\begingroup$ An Eidophor is just a specific type of projector, there's nothing wrong with the other answer. This should really be a comment. $\endgroup$ – Organic Marble Jul 3 at 16:09
  • $\begingroup$ The question concentrated on the projectors for the maps of Moon and Earth, not on the low resolution analog video projectors. $\endgroup$ – Uwe Jul 6 at 20:46

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