3/15/2026 at 5:00:06 PM
I remember an anecdote our robotics lecturer told our university class in 1995, which was about how in the west we try to make expensive things that are the absolute best of technology and how the other side didn't have that luxury and relied on ingenuity.He described a cold war Russian missile they had somehow obtained and were tasked with trying to reverse engineer. Ostensibly, it was thought to be a heat seeking missile, but there seemed to be no control or guidance circuitry at all. There was a single LDR (light dependent resistor) attached to a coil which moved a fin. That was it. Total cost for the guidance system maybe a couple of dollars, compared to hundreds of thousands for the cheapest guidance systems we had at the time.
The key insight was that if you shined a light at it, the fin moved one way and if there was no light the fin moved the opposite way. That still didn't explain how this was able to guide a missile, but the next realisation was that the other fins were angled so when this was flying (propelled by burning rocket fuel), the missile was inherently unstable - rotating around the axis of thrust and wobbling slightly. With the moveable fin in place, it was enough to straighten it up when it was facing a bright light, and wobble more when there was no bright light. Because it was constantly rotating, you could think of it as defaulting to exploring a cone around its current direction, and when it could see a light it aimed towards the centre of that cone. It was then able to "explore the sky" and latch on to the brightest thing it could see, which would hopefully be the exhaust from a plane, and so it would be able to lock on, and adjust course on a moving target with no "brain" at all.
by ralferoo
3/15/2026 at 8:39:06 PM
That's roughly how the original Sidewinder worked. The original concept was to reduce near-misses. If the pilot could get on the target's tail and aim at the engines, it usually got a hit. That was the same task as getting into firing position for guns. Hit rate about 8% in combat.Later versions allowed launches from longer ranges and from off-angles.
by Animats
3/15/2026 at 5:12:46 PM
I believe there was a similar weapon being developed in the west, only recently, which involved a missile with contra rotating halves joined by a clutch. The fixed fins caused it to always steer one way. It flew straight by releasing the clutch to spin up the front half, negating the steering effect. Grabbing the clutch caused it to stop spinning and veer off in one direction.Presto! Two axis continuous flight control with a 1-bit input.
Edit: my memory wasn’t far off. It’s Starstreak: https://en.wikipedia.org/wiki/Starstreak
by gorgoiler
3/15/2026 at 5:34:53 PM
35-ish years ago there was a pitch for cheap, high velocity, spin-stabilized rockets that were deployed in dense pods on the A-10. The rocket's seeker could divert some small amount of thrust at an angle for guidance, but otherwise that was it. I can't recall if it ever made it out of the pilot phase, but obviously nothing new under the sun.by coredog64
3/16/2026 at 12:52:02 PM
I think the Ukrainian Stugna & other ATGMs (not only with soviet heritage) use the rotation trick - you get some stabilization for free, might need less control surfaces and maybe even simpler sensors.IIRC in the Stugna case, they even use solid fuel micro motors - they have a couple dozen of them in a rignt near the nose and fire them as the missile rotates in flight providing a kick in the right direction to hit the target. Given the missile usually flies for <30 seconds, this is perfectly adequate versus a complex set of aerodynamic actuators.
by m4rtink
3/15/2026 at 5:13:00 PM
Strike a light in front of a parked but otherwise active fin guided heat-seeker and its freaky to watch it come alive like a lazy beagle eyeing a treat.by srean
3/15/2026 at 10:13:21 PM
Is there a video of that on YT?by inglor_cz
3/16/2026 at 8:56:27 AM
Got curious. It's not a lighterby srean
3/15/2026 at 6:57:48 PM
This is shockingly similar to microbial motility mechanisms. Like random walk plus chemotaxis.by snitty
3/15/2026 at 7:56:56 PM
This sounds like the early Sidewinder or other 1940's/1950's attempts at infrared homing missiles.by mapt
3/15/2026 at 10:47:15 PM
This is an interesting thought, as if I remember correctly, there was this theory that once something is known to be possible to discover, it only takes dedication to achieve it (George Dantzig as an example)by 3abiton
3/15/2026 at 8:14:18 PM
That frugal, creative mindset is also the default for people of modest income everywhere in the world - borne of necessity.by crtified
3/15/2026 at 5:08:42 PM
Unless it was nighttime or the engagement happened at low altitude on a cloudy day, wouldn’t that usually lock onto the sun?by chroma
3/15/2026 at 5:35:12 PM
The wobble would only 'scan' a limited field of view, so only if the sun was in that viewby bluescrn
3/15/2026 at 7:29:50 PM
Also wouldn't it only work for aircraft that are flying away from the launcher? IR & light signatures are much weaker from the front. At best I think this guidance system would only be economical for ground-based launchers, as the cost of aircraft and their limited payloads mean you want the most effective weapons onboard, not the cheapest.Annoyingly, I can't find any information online about such a simple guidance system. The earliest homing missile fielded by the Soviets was the K-13[1], which used technology reversed-engineered from the AIM-9 Sidewinder[2]. Later systems seem to be improvements upon that technology, not simplifications.
by chroma
3/15/2026 at 7:36:25 PM
> Also wouldn't it only work for aircraft that are flying away from the launcher?Yes, pretty much all early guided missiles of the sort were what's called "rear-aspect".
Can't see the plume - can't make a boom.
by Tadpole9181
3/15/2026 at 5:07:06 PM
Similar to how moths guide themselves toward lightby dosssman
3/15/2026 at 7:11:38 PM
that sounds like crude-fied version of first Sidewinders.by trhway
3/15/2026 at 5:04:15 PM
Incredibleby Gud
3/15/2026 at 8:21:01 PM
> That still didn't explain how this was able to guide a missileThat does explain why it lands on civilian areas tho
by dzhiurgis
3/15/2026 at 7:26:23 PM
> with no "brain" at allIt seems this is how Russia moves in general. Hopefully, this will end at some point.
by dandanua