[tyingq]

Here's my guess. Government bureaucracy is probably very high for anything space related. So "based on the military's AN/UGC-74" could have helped get it through approvals. It would have ticked a lot of boxes for ruggedized parts, use in harsh environments, and so on.

[beerandt]

I don't doubt that for a second- but I'm more curious about the requirement for some kind of printout in the first place.

Especially since it ultimately ended up weighing what it did.

Military/ Ruggedized is a smart choice for a printer that needs to go through that environment, no matter the why.

I'm more interested in what it tells us about the underlying purpose (or what it might rule out, like the part about wired directly into unencrypted comms).

[jcrawfordor]

I don't think the requirement for printed output requires any appeal to military applications. They would have been exchanging navigation information with mission control over the radio. That's all mission critical and needs to be read back. Anything they got via voice they would have to write down. Getting it by text in the first place would increase reliability and reduce cockpit workload.

You also get in-flight information like weather that you'll want to write down for later reference. Teleprinter writes it for you so you can review it at your leisure.

Airliners and ships at sea have both historically used teleprinters for the same reasons, although the modern navigation computers have mostly eliminated the need.

[tyingq]

Oh, I didn't consider that, since I was a young person then. Sticking notes, directives, etc, everywhere was just really common. So if they get a note about extra daily checks on equipment X, they print/affix the note to the equipment. Or other similar needs. There would probably be limited screens, so anything you wanted to be known to everyone, becomes a note.