21–28 of 28 posts
Author here if you have questions...
Convective heat transfer in metal would be a worrying event on the Space Shuttle!
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How did the voting work? The first thing I thought was, what happens in a tie (2-2) vote?
It's unlikely that you'd get a simultaneous tie; you'd expect one computer to go bad before the other. But I think in that case, the astronauts switch to the Backup Flight System, the fifth computer. Mission STS-9 had two computer failures, causing landing to be delayed by 7 3/4 hours. They carried a sixth computer as a backup for following missions. As far as how the voting works, each computer has a signal indicati…
The story was that they were planning to fly with 3 computers, and that they would "vote" on important decisions.
The real trick was that they intended to build those computer with 3 separate teams, using clean room implementation (no coordinating with the other teams), and that they were going to use 3 separate CPU architectures, and even 3 different implementation languages.
As I understand it, they conceded on the language choice, they were all going to use the same language, but I don't know about the rest.
The goal was to avoid some catastrophic "unknown unknown" that might have crept into the implementation if they simply rolled out 3 copies of the same system.
Author here if you have questions...
Amazing article, thanks! However, I think when you said "...heat was transmitted by convection through the metal plate inside each page...", you probably meant conduction, right? Convective heat transfer in metal would be a worrying event on the Space Shuttle!
To me, these correspond more or less 1:1 with PIO instructions OUT, IN, SET, INT, and WAIT. These plus PUSH, PULL (which can considered auxiliaries of IN and OUT), MOV, and JMP are all the PIO instructions. Like the BCE, it runs with completely deterministic clocking, one instruction per clock, and like the BCE there are a bunch of them (a total of 12 state machines on the 2350), though they now run totally in parallel rather than being time-multiplexed.
As a hobby project, I've lately been implementing USB (aiming for higher performance than Pico-PIO-USB, which proves that it's possible), and that's been quite fun.
I wonder to what extent they were explicitly inspired, and to what extent you just get convergent solutions when there are similar goals and constraints.
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Yes, the low density and TTL chips (instead of MOS) helped against radiation. When the Shuttle computers moved to semiconductor RAM, they needed extensive error correction, as well as a process that constantly fixed bit errors, as the memory would get multiple errors per flight due to cosmic rays. As far as redundancy, it's complicated. During critical flight phases, four computers would run the main software (PASS,…
what a treasure-trove of historical technical info you have do you know anything about the military's secret space-shuttle still in operation? I'm sure it's either been very modernized or runs on completely different design since it's supposedly remote-control
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what a treasure-trove of historical technical info you have do you know anything about the military's secret space-shuttle still in operation? I'm sure it's either been very modernized or runs on completely different design since it's supposedly remote-control
How could it be possible to conceal the movement of such a huge thing?
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what a treasure-trove of historical technical info you have do you know anything about the military's secret space-shuttle still in operation? I'm sure it's either been very modernized or runs on completely different design since it's supposedly remote-control
How could it be possible to conceal the movement of such a huge thing?
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Did Shuttle fly with these bodge-wired boards or were these used for development on the ground?
I don't know if these boards were flown. They were coated with conformal coating (which I hate for reverse-engineering), which is usually omitted from prototypes. I believe that bodge wires are okay for flight if they are done properly.
Bad memory from a couple years ago. Debugging a machine under development at a customer site, which was luckily only a few blocks from the office, since I was there a lot, I would get random resets, hangs, and loss of debug information from the SWD probe. Swapping boards, debug probes, nothing we could think of fixed it and it was so random it was hard to track down.
Long story short, after it happened on one occasion when the project EE was also debugging something and he touched one of my probes, we found that there was conformal coat residue on some of the debug pins and the probes would occasionally vibrate onto an insulated section, causing loss of signal.
No idea why the board house put it on a prototype, but we probably lost a few dozen hours due to that one problem.