You've seen the videos of old-school NASA mission-control from the 1960s, with those huge, wall-sized screens — which displayed bright lines showing the flight path of spacecraft, and flight data.
How the heck did they do that? They didn't have wall-sized LCDs back then.
Over at her phenomenal YouTube channel, Fran Blanche did a fantastic excavation of old documents, photos and videos to explain what was going on. It turns out it was a super analog process — it was done with projectors, and the little icons (of, say, spacecraft) were small slides. As she explains in the video…
So these large projection displays, these colorful, sharp, multicolored displays are made up of overlapping projections of monochromatic slides — these slides are about one inch square each. They're glass slides, not film. And each one is essentially just a black and white image, a piece of glass with a metal film deposited on it that is then etched to have a particular black and white icon or a shape to have lettering or the details of a map or an icon of a spacecraft.
The color comes from filters, and they're illuminated by insanely bright xenon lights. The slides needed to be metal film on glass because those xenon lights were so insanely hot, and needed to be lit for days at a time.
So yeah, all the stuff you see here — that's slides …
As spacecraft flew, the displays could also plot a line that would grow and extend, showing the flight path. How do you do that with slides?
By having some of the projects contain plotters that could scrape a path onto a slide, in real-time. As Blanche describes it …
Four of those five projectors were plotters which were equipped with these special diamond tipped scribes, and they were driven from servos to move a scribe across a slide which was coated completely opaque with a metal film. And as the scribe went across the plate, it would scrape away a tiny little ribbon of metal film and light would be able to project through. And then that light could be colored with any color that they wanted that was in the carousel using any one of the filters that they had available.
There's a ton more crazy-fascinating detail here; go watch the whole thing, and subscribe to her channel. Blanche's work is always amazing, but with this video she really knocked it out of the park.