https://en.wikipedia.org/wiki/TERCOM
Notably how it fit on older computer systems with limited memory by only sampling the terrain using a predefined path which a plane will travel over with imaging sensors beforehand. For minutemen style systems with predefined targets it would work well as the terrain won’t change significantly and there will be plenty of sampling data to support a high error rate and/or a relatively low resolution while moving at high speeds.
Of course it increased in quality and effectiveness over time (especially as whole topographical maps could eventually be stored, not just the path in question) but as an entirely ‘unguided’ rocket it seems to be relatively accurate for its era.
> At launch, orders from the National Command Authority would have specified one of three pre-programmed targets which, for security reasons, were unknown to the crew. ... Target 2, which is classified to this day but was assumed to be within the borders of the former Soviet Union, was designated as a ground burst, suggesting that the target was a hardened facility such as a Soviet missile base. [Wikipedia]
While explaining this, my tour guide showed some punched tape that could be fed into a computer to program the targets. I wonder if the tape was original, and if so, how difficult it would be to decode its coordinates.
I'd be very surprised. We used punched tape for initializing our crypto gear when I was in the Air Force, and it was accounted for carefully and destroyed promptly. Even more carefully than our regular classified documents, though maybe that was just a culture thing. I can't imagine them just giving it over to a museum.
I wondered the same thing about the punched tape, if I could extract the coordinates from it. I read somewhere that they were extremely strict about keeping the targets secret; before any maintenance on the computer, a special team came in just to ensure that the coordinates were erased from memory. It would have been a huge oversight if they didn't encrypt the punched tape, so my guess is that it can't be decoded.
So even two missiles/warheads launched from different sites at the same target would have different guidance instructions.
You'd need to do some major reverse engineering and geodetic calculations even after decoding targeting punchcards to figure out what the actual targets were.
The punchcards used to select the target during launch are simply instructions to execute "target stored in memory 2" or something similar. The minutemen would not have had the ability to change the set of targeting options programmed in the missile, only select one of the pre-programmed options.
Prior to the socket being dropped, there was a change order issued to use a new type of socket that would not dislodge from the wrench. As I recall, the two technicians tasked with the repair didn't have the new type of socket, but proceeded into the silo anyway.
https://archive.org/details/commandcontrol00eric (OpenLibrary)
Motorola made "MTTL II" which had 20xx part numbers for commercial temperature range and 21xx for industrial/military, so these could be Signetics' variant of that. In the late 60s through the 70s semiconductor companies made lots of different logic families.
I've always found it a bit sad that the ultimate purpose of things like this was for destruction.
As far as your last point, I basically agree. This computer, though, is not quite as bad as it could be. It was a later, 1970s model originally designed for the Titan IIIC rocket to put satellites into space, a more positive role. It was also closely based on the Carousel IV commercial navigation system used for aircraft such as the Boeing 747, which is a nice heartwarming application.
Edit: the Motorola 21xx parts have the wrong pinout, e.g. ground on pin 10 vs 11. And many of the numbers don't exist as Motorola parts. Unfortunately, I don't think these are the right parts, although it seems so close.
I imagine it was much heavier than an equivalent active system.
I guess MPG doesn't matter much on a Titan missile.
But a passive system has a few major advantages - it's maintenance free, unlike an active system (imagine having to fill up the coolant tank before launch), and perfectly reliable. Sure, a phase-change coolant might be more efficient - but with flight times in the hours I'm not sure that the difference would be enough to compensate for the complexity.
