Бортовые Часы Космические
January 19, 2020 11:15 AM   Subscribe

We recently obtained a clock that flew on a Soyuz space mission. The clock, manufactured in 1984, contains over 100 integrated circuits on ten circuit boards. Why is the clock so complicated? In this blog post, I examine the clock's circuitry and explain why so many chips were needed. The clock also provides a glimpse into the little-known world of Soviet aerospace electronics and how it compares to American technology.
posted by zamboni (19 comments total) 33 users marked this as a favorite
Ken Shirriff previously
posted by zamboni at 11:18 AM on January 19 [1 favorite]

From the footnotes:

So why did the Space Shuttle [like Soyuz] use mostly-obsolete TTL technology in the 1980s redesign? One reason was backward compatibility. Since the first Shuttle computer used the proprietary IBM 4π architecture, it couldn't be replaced by an off-the-shelf microprocessor. Reliability was another motivation for TTL. Commerical microprocessors weren't designed for the reliability needs of space systems and lacked features such as radiation resistance and parity-protected caches. Finally, the aerospace development cycle is very long; although the Shuttle computer redesign started in 1982, the computer wasn't used on a flight until 1991 and remained in use until 2011. The point is that there were reasons to build aerospace systems from TTL, even though microprocessors were much faster, more compact, and lower power.
posted by justsomebodythatyouusedtoknow at 11:37 AM on January 19 [2 favorites]

All the reasons make sense, but still - I think about what that thing must weigh, and the rocket equation, and the sheer physical and budgetary cost of launching all that reliability, flight-provenness and backwards compatibility on every subsequent flight - multiplied by dozens of similar systems.
posted by automatronic at 11:48 AM on January 19 [1 favorite]

This interesting initially just for the topic, but personally because I
just ran across Ken Shirriff from a slightly different angle last week.

I’ve been teaching myself electronics with Arduino etc. and he wrote what was for me the most useful tutorial on IR media remotes.
posted by hwestiii at 11:54 AM on January 19 [1 favorite]

Very cool. My first though on why both the US and the USSR were still using TTL chips for spacecraft clocks in the mid-80s was also for radiation resistance. I'm no expert but my understanding is that CMOS is more sensitive to cosmic rays, which have a noticeably greater effect at increasing altitude, so maybe there was concern that using more modern chips would compromise reliability. TTL chips had already been field-tested and I suppose found to be sufficiently resistant to cosmic rays, so perhaps the risk of adopting CMOS wasn't seen as worth it. Of course I'm sure modern spacecraft use CMOS without problems, but it makes sense that both space agencies would be slow to change something that already worked.

Probably it was a combination of lots of factors like the ones Shirriff speculates about in that footnote.
posted by biogeo at 12:20 PM on January 19

This Ars Technica article talks about modern space-worthy processors.
posted by sjswitzer at 12:27 PM on January 19 [4 favorites]

I’ve been teaching myself electronics with Arduino etc. and he wrote what was for me the most useful tutorial on IR media remotes.

...also he wrote the libraries.
posted by pompomtom at 1:48 PM on January 19 [2 favorites]

Fascinating article. I don’t know much about integrated circuits but it was an interesting explanation of why a state-of-the-1980’s-art space clock needs a hundred chips when contemporaneous clock radios that could do the same thing cost twenty bucks at Radio Shack.
posted by ejs at 3:00 PM on January 19

CMOS ICs are also more susceptible to static than TTL chips - a jolt of static electricity will kill them forever. I wonder if that's more of a problem/concern.

More than anything I'm surprised at how much wiring there is, like the author I would have expected edge connectors instead of cable bundles.
posted by RustyBrooks at 4:42 PM on January 19

I would buy a clock that looks like this and put it on my shelf. It could be powered by a $9 Arduino clone inside, I don't care. But I want the clock.
posted by Jimbob at 4:58 PM on January 19 [2 favorites]

Here's a TTL clock kit for your clock building pleasure.
posted by monotreme at 6:42 PM on January 19 [3 favorites]

The wire bundles are used because they are more resistant to vibration and shock than the other options.
posted by BeeDo at 11:31 PM on January 19

Pompomtom: that is what lead me to the tutorial.
posted by hwestiii at 2:23 AM on January 20 [1 favorite]

CuriousMarc's YT channel is great. He did a long series on the Apollo Guidance Computer, and has done several pieces on old mainframes. Plenty to dive into.
posted by xedrik at 6:49 AM on January 20

My son and I built a digital clock from chips and wires about 10 years ago. It seemed needlessly complex, a huge tangle of wires that I barely could comprehend (but my whip-smart eight year old totally grokked). I guess we didn't do too bad after all! We tried reproducing it on a soldered circuit board, but we could not get good enough at soldering. I think I understand the need for so much power regulation and isolation: our clock would reset itself a lot seemingly at random. There's a lot I imagine you would want to do for must-not-fail gear that you wouldn't bother with for a regular alarm clock. If they were timing their burns and maneuvers using this thing, if it conks out at the wrong time your cosmonauts are all dead.
posted by rikschell at 7:42 AM on January 20 [1 favorite]

More information on Soviet semiconductor logos can be found here and here.

If you click those links you briefly feel like you're living in a William Gibson novel.
posted by thatwhichfalls at 8:30 AM on January 20

Very weird. A Casio watch of the same era could have done the same job.
posted by w0mbat at 12:34 PM on January 20

Here's a TTL clock kit for your clock building pleasure.

I've built the Transistor Clock kit from that guy. It was one heck of a lot of parts (around 1250!) to solder.
posted by fimbulvetr at 1:36 PM on January 20 [2 favorites]

Youtube channel "CuriousMarc" just posted another vid about this clock.
posted by maxwelton at 11:25 PM on January 20

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