Technology has moved at such a furious pace that what would have been most secret military technology a few decades ago is now surplus on eBay. Case in point: [msylvain59] picked up a Soviet-era K-13 IR seeker used to guide air-to-air missiles to their targets. Inside is a mechanical gyroscope turning at over 4,000 RPM, a filter made of germanium to block visible light, and a photoresistor. It’s sobering to think you can get all of this in a few small packages these days, if not integrated into one IC.

Fitting on top of a missile, the device isn’t that large anyway, but it is nothing like what a modern device would look like. A complex set of electronics processes the signal and moves steering actuators that control fins and other controls to guide the missile’s flight. You can see a video of the device giving up its secrets, below.

It isn’t just the IR sensor that looks different from a modern design. The actuators, the control logic — everything, really — we would do in a much easier way today. Of course, you’d still have to make sure the equipment met shock requirements of the launch, although perhaps not the impact. But if anything, that would be easier with fewer smaller components.

Honestly, we got winded just watching him remove the outer housing. Then there was plenty of potting material — probably to help with shock resistance and environmental requirements.

We will agree you probably won’t ever design an IR tracker for a warhead. If you did, it wouldn’t look at all like this. But it is illustrative to look at how designers made things work without the host of microcontrollers and miniature devices we have today.

If you want to understand more about how all gyros work, start here. We don’t know what the K-13 cost new, but we know this much less complex gyro cost about $15,000 in today’s dollars.