The guidance system and computer of the Minuteman III nuclear missile

The article states that the system was cooled using a solution of sodium chromate to inhibit corrosion. However the wiki page of sodium chromate states that it is very corrosive. Is it a typo or something?

It's also mentioned that the computer uses one of the first integrated circuits for miniaturization. Do you know if this can be definitely traced to advances in industrial/consumer products? It's a common trope that military research trickles down - so it's a "good" thing. It's not clear if this actually happens or if progress would have been made eventually without the need for these machines.

philipkglass• 2 years ago

Chromates are effective corrosion inhibitors for aluminum alloys and some other metals. Here's a brief article about how they work with aluminum:

"Inhibition of Aluminum Alloy Corrosion by Chromates"

https://www.electrochem.org/dl/interface/wtr/wtr01/IF12-01-P...

When the Wikipedia entry's "Safety" section says that sodium chromate is corrosive, in context it means "destructive to human tissue by contact." That is, like sodium hydroxide (lye) and many other chemicals, in concentrated form it can destroy skin and eyes.

kens20• 2 years ago

Sodium chromate is highly corrosive to humans (as well as carcinogenic, see the movie Erin Brockovich). However, it inhibits corrosion in metal, acting as a passivating inhibitor, forming some sort of protective oxide.

I've been doing a lot of research on the impact of Minuteman and Apollo on the IC industry (which led to the current post). The Air Force likes to take credit for the IC industry, as does NASA, but the actual influence is debatable. My take is that both projects had a large impact on the IC industry, more from Minuteman. However, even in the absence of both projects, there was a lot of interest and demand for ICs. If I had to take a quantitative guess, I'd say that those projects advanced ICs by maybe a year, but the basic trajectory would have remained the same.

izacus2• 2 years ago

How does a 1-bit serial computer actually work? E.g. how does an ADD operation look like? It's a bit hard to picture.

kens20• 2 years ago

In a serial computer, you have a 1-bit ALU, say an full adder that generate a sum and carry. Each clock cycle you read two bits and feed them into the adder, and then you write back the sum. You hold the carry in a flip-flop to use in the next clock cycle. It's just like doing a binary addition with pencil and paper, one bit at a time.

Note that you need to start with the lowest bit with a serial computer, which explains why x86 is little-endian. It goes back to the Datapoint 2200, a desktop computer made from TTL chips and running serially. The Intel 8008 processor was a copy of the Datapoint 2200 (as was the Texas Instruments TMX 1795). Although the 8008 was parallel, it copied the little-endian architecture of the Datapoint 2200.

kragen4• 2 years ago

if you write down two binary numbers on paper and add them, you will almost certainly do the computation bit-serially, adding each pair of corresponding bits with the carry from the previous operation. serial computers work the same way

bloopernova• 2 years ago

Do you have any plans to write about World War 2 era mechanical firing computers? I searched your blog but didn't see anything.

Or maybe early RADAR systems of 1942 and later?

(been reading about WW2 Pacific naval/air wars, and I am curious about these new-at-the-time technologies)

kens20• 2 years ago

I planned to write about the electromechanical Torpedo Data Computer used in WWII, but I got distracted.

nullhole2• 2 years ago

Any opinion on the book 'Inventing Accuracy'? It covers the Minuteman guidance system for a few chapters.

kens20• 2 years ago

I've got the book on my desk right now :-) It's a bit of an unusual book because it is full of technical details but it also has a fair bit of sociological content like "the construction of technical facts", "technological determinism", and "sociology of technological knowledge". This is in contrast to, say, "Minuteman: A Technical History", which is strictly facts and details. They are both good books, but it is interesting how they have completely different styles and focuses.

bun_terminator2• 2 years ago

I have a morbid curiosity to know how much of all that old tech would actually work in a full scale nuclear war, launching all missiles. Seems so well thought-out, but also incredibly hard to test. Really fascinating article!

akira25013• 2 years ago

Why would it be hard to test? We have our own anti-missile technology, so it's ostensibly as simple as not putting a payload on the missile, then launching it at your own test range.

dumah• 2 years ago

The physical environment these weapons were designed for is extreme and only possible to simulate piecemeal.

Each stage needs to function in the presence of nearby nuclear detonations, resulting from both adversary and friendly weapons.

These detonations are expected to cause severe shock, thermal, radiation, and electromagnetic transients.

In the case of the most important targets, it is guaranteed that numerous detonations near the target, from ABM systems and friendly impacts, will occur, and these systems have been engineered and are expected to perform reliably under such conditions.

bun_terminator2• 2 years ago

I was thinking mostly of the bits of the tech designed for working when the launch site is hits with nuclear explosions

kens20• 2 years ago

They did dozens of tests of the Minuteman missiles and reentry vehicles. The warheads were tested underground until the comprehensive test ban treaty of 1996. So it's pretty likely that the systems would work if needed. One risk is that something may have gone wrong with the warheads over 30 years. (Of course they maintain them, but without testing you can't be sure.) Another risk is that you don't know how the missiles would function in an environment with nuclear blasts and EMP all over the place. They put a whole lot of effort into mitigating these factors, but you can't be sure. Hopefully we never find out.

leeter• 2 years ago

Note: While none of the Annex 2 countries that are signatories have conducted tests since 1996; the treaty never took effect because it was never ratified by all the required countries. Most notably the US, China, and Russia (although all three signed). In 2023 Russia officially withdrew, allegedly based on the US non-ratification. At least one political candidate for the presidency in the US has advocated for resuming testing. It is not inconceivable that testing could resume in the near future.

Opinion: I don't think the US would if Russia or China didn't first. China likely won't for the same reason the US doesn't need to: they have super-computers and the sims line up with the data from prior tests. Russia might however if only to saber rattle, although they likely don't need to either. Russia however is likely not in any hurry to have a test failure right now. So while testing could resume, I wouldn't put money on it.

Joel_Mckay2• 2 years ago

There was an area of redundant symmetric electronic design, that auto compensated for component level failures. I remember reading an "aerospace" manual all about it when I was a kid. It was necessitated when the tolerance and reliability of components were terrible by today standards.

Note too, that mil spec silicon is different in that it is resistant to CMOS latch-up, redundant CRC protected self-correcting consensus register ops, and large gate sizes less sensitive to Gamma radiation.

It was an interesting time, and a few people still think living under the Sword of Damocles builds character. =3

detourdog2• 2 years ago

Here is a link to a bunch of artifacts from of those computers and their development.

https://www.icloud.com/sharedalbum/#B0YG4TcsmGWIVSf

Ringz• 2 years ago

Impressive work and very interesting! Since I was instantly interested in the tiny „window“ and its purpose I found a little error:

„Aligning the missile was a tedious process that used the North Star*t* to determine North.„

kens20• 2 years ago

Thanks! I fixed that.

firesteelrain• 2 years ago

Your article on the guidance system reminds me of this https://youtu.be/bZe5J8SVCYQ?si=LuVwiZ7NEI21czoH

kens20• 2 years ago

I refrained from including that link :-)

beerandt10• 2 years ago

Even as someone who's actually done the math that video is trying to explain(in an actual class covering missile geodesy), it's still so absurd.

But honestly only about half as crazy as GPS would sound if you tried to put it in similar terms. And that's before considering the signal itself is way below the noise floor.

As much as I love these technical writeups, I wish more people who understand the slightly expanded bigger picture/ implications of the missile technologies would write what they know before the generation goes extinct.

There's so many dots that are easily connected from articles like these... but I suspect some level of classification prevents those in the know from being able to publish.

The bulletin of atomic scientists is the only non-fringe source that ever comes close. (Their article on the new generation of warhead fuses is a great resource for those wanting to go down the rabbit hole. Even it now seems to have been scrubbed from their site. [0])

[0] https://web.archive.org/web/20170307194641/https://thebullet...

Eta working bulletin link: [1]https://thebulletin.org/2017/03/how-us-nuclear-force-moderni...

minkles4• 2 years ago

Ha that's great. I was expecting this for some reason https://www.youtube.com/watch?v=yXFh54fc8GM

benjam475• 2 years ago

I live several miles from a Minuteman silo in Montana, maintained by Malmstrom Air Force Base. The underground cabling between sites is also an interesting read (https://minutemanmissile.com/hics.html). Anytime I want to dig on my property, I have to make sure it won't interfere with their pressurized cables. I have heard a story from someone that did accidentally cut a cable, and Malmstrom AFB was able to locate the break and respond rapidly. I am a volunteer firefighter, and our station has a VHS tape and a paper guide titled "Incident Guide for Missile Field Fire Response" provided to us by the DoD regarding our role in responding to fiře incidents near or at a silo. A year or so ago, we did respond to a fire near a silo, but it occurred entirely outside the security fencing. My understanding is that the personnel at the silos also have their own ability to respond to fires.

nonethewiser• 2 years ago

Anytime I want to dig on my property, I have to make sure it won't interfere with their pressurized cables.

Sounds like a serious weak point

cpgxiii3• 2 years ago

The missile silos and control facilities are connected in a sort of semi-mesh topology, so any one cable break is unlikely to cause a communications failure. There are backup launch control interfaces available via airborne platforms (specifically the E-6 today) as well.

Digging into one of the cables is going to get you a prompt and unpleasant visit from base security.

preisschild• 2 years ago

They have redundancy. But they obviously want to know where it happened in case it was sabotage.

bunabhucan• 2 years ago

Image showing the layout/redundancy of the communications:

https://en.m.wikipedia.org/wiki/LGM-30_Minuteman#/media/File...

There are alternate ways to launch the missiles (e.g. radio from a plane) in the event of an attack.

kev009• 2 years ago

The tape is probably a reponse to some infamous disasters/tragedies:

* https://en.wikipedia.org/wiki/LGM-25C_Titan_II#Mishaps

* https://en.wikipedia.org/wiki/1965_Searcy_missile_silo_fire

* https://en.wikipedia.org/wiki/1980_Damascus_Titan_missile_ex...

beerandt10• 2 years ago

How different is it than a standard 811 utility-locate call?

Actual change in procedure? Or just extra cheek-clinching?

benjam475• 2 years ago

Today it is the same thing (part of an 811 call). In the distant past, it was a separate call.

Around 2000 land owners are affected, and anecdoctally it seems to add a few days to a 811 response (~a week instead of 2-3 days).

JoeDaDude• 2 years ago

But isn't it the case that there is typically no personnel at the silo (or Launch Facility LF) itself? Instead, the Missile wing Commanders at the Launch Control Centers (LCC) some distance away. The LCC commands some number of LFs remotely.

https://en.wikipedia.org/wiki/Missile_launch_control_center

benjam475• 2 years ago

Good question. They definitely do have launch control centers. All available information online does seem to indicate that is the case that the silos themselves are unmanned. My understanding is that there was some security on site, but that is just based on second hand stories I've heard, and may not be true.

I do see military vehicles traveling to and from the one that I am close to semi regularly, perhaps a month or so on average.

As far as fire response, they likely have their equipment for that at the control centers as well.

minkles4• 2 years ago

Just a bit of additional trivia. Jim Williams (somewhat famous EE at Linear) had a minuteman computer on his living room wall known as "the tapestry": https://www.eetimes.com/photo-gallery-remembering-jim-willia... (last picture in particle). Not sure what revision.

kens20• 2 years ago

Those boards are from the Minuteman I, the cylindrical computer. I wonder what happened to his boards?

minkles4• 2 years ago

Thanks for confirming (and thanks for the excellent article btw). I wish I knew for sure. Anything of that nature deserves to be carefully preserved.

blantonl• 2 years ago

These systems are so vastly complicated, old, and rarely if ever launched. These aren't like data center generators which have testing schedules etc, and STILL there are failure points.

I really wonder what the failure rate would be if they were all actually launched today. And I mean failure, from not lifting off, to failure in flight, to misguided warheads etc.

minkles4• 2 years ago

They have operational models with statistical failures included so they understand what the interception and failure probabilities likely are for each item at component level. You can design that into a system and test for it.

Obviously you can't factor in unknown problems but that's what drills and test flights are for.

krisoft4• 2 years ago

But they do have testing schedules. They certainly tests the electronics regularly. And every so often they randomly pick a missile and launch them from Vandenberg.

https://www.spaceforce.mil/News/Article-Display/Article/3796...

I really wonder what the failure rate would be if they were all actually launched today

I hope we will never find out. But certainly there would be many duds. But this is calculated into the effectiveness of the system by simply having more missiles. That is how it achieves its goal of dettering a would be attacker. (Not even talking about how there are two other totaly separate legs of the nuclear triad with dissimilar personel and technical solutions.)

m_mueller• 2 years ago

randomly pick a missile and launch them from Vandenberg

Jeff! Did you remember to take out the warheads? Jeff?!

dboreham2• 2 years ago

Air force takes one at random, transports it to Vandenberg sans warhead and lights the fuse to see if it works. Or at least they used to. I also heard that the Soviet equivalent of this random testing process was to simply retarget a random missile and launch it straight out the operational silo.

cpgxiii3• 2 years ago

Strategic weapons are tested regularly, except for the warhead. The Trident II D5 has had about 200 tests in the last 35 years. That's about the same number of test missiles expended as are actively deployed at any given time. While there are a theoretical maximum of 344 deployed at any one time (14 Ohio-class, each with 20 tubes, plus 4 Vanguard-class with 16 tubes) some number of those boats are unarmed in refit at any given time.

justin663• 2 years ago

You can watch video of the most recent test, a little more than a month ago, of a Minuteman III. This is a short clip:

https://www.youtube.com/watch?v=zUg7x1zo7D0

They can test the missiles and reentry vehicles, everything except the nuclear warhead. The closest those come to a test is a supercomputer simulation, since those tests are forbidden by treaty.

Minuteman III has an excellent but not perfect [0] failure rate. Some other older systems, like the UK's submarine launched Trident missiles... not so much.

[0] https://www.airandspaceforces.com/icbm-test-failure-nuclear-...

arethuza3• 2 years ago

Th UK Trident 2 missiles are literally the same missiles used by the US submarines operating in the Atlantic - both sets of submarines are supplied by a shared pool:

https://en.wikipedia.org/wiki/UGM-133_Trident_II

However, the warheads on the UK missiles are designed and manufactured by the UK.

jonathanyc3• 2 years ago

The new guidance platform also added a gyrocompass under the alignment block, a special compass that could precisely align itself to North by precessing against the Earth's rotation. At first, the gyrocompass was used as a backup check against the autocollimator, but eventually the gyrocompass became the primary alignment. For calibration, the alignment block also includes electrolytic bubble levels to position the stable platform in known orientations with respect to local gravity.

Had never heard of gyrocompasses before. I worked on a small robot in the past and remember having to calibrate the magnetic compass, which was not very accurate (similar to smartphone compasses). I never thought about how they’d get super precise headings for ICBMs.

The Encyclopedia Britannica article on gyrocompasses is really good. Here it explains why you can’t use a gyrocompass on a vehicle on fast aircraft (and I guess small robots that are jostled around a lot):

A major contribution by Schuler was the discovery that, when the period of oscillation is 2π√(Earth radius/gravity), the heading precession of the gyroscope spin-axis due to acceleration is exactly the rate of change of the angle between the apparent and true meridians seen on a moving vehicle. The gyrocompass will then read true north at all times if its indicating reference is offset by the angle between these two meridians. The angle, at ship speeds, is a direct function of the north-south speed and is easily set into the system. The need for accurate speed measurement for this offset is the main reason why a gyrocompass is not practical for use in aircraft.

https://www.britannica.com/technology/gyrocompass

Love this article!

maxglute• 2 years ago

What's the actual color of the yellow paint? Goldish like first pic of lemonish like latter pics. Contrast/aesthetics of the gold is just chefs kiss. There's something about American MIC pallette that rarely miss.

ornateelephant• 2 years ago

It's the corrosion protective primer, usually containing zinc chromate. Colours may vary slightly but they are usually some shade of yellowy green.

https://aviation.stackexchange.com/questions/49961/why-are-a...

tempaway4575144• 2 years ago

The idea behind inertial navigation is to keep track of the missile's position by constantly measuring its acceleration. By integrating the acceleration, you get the velocity. And by integrating the velocity, you get the position.

This sounds like it couldn't possibly work (surely all the little errors compound?) but apparently it's how Apollo navigated

https://wehackthemoon.com/tech/inertial-measurement-unit-mec...

Zircom• 2 years ago

I mean it's a nuclear missile, millimeter accuracy isn't really necessary. Somewhere in the general vicinity is good enough for it's purpose of going boom.

nox101• 2 years ago

shooting something 12000 miles away, 0.1% off is 12 miles. That's missing the target and will not destroy whatever you were trying to destroy

kens20• 2 years ago

Well, accuracy makes a big difference if you're trying to hit a hardened target like a missile silo. Missile guidance has been a constant effort to squeeze out more and more accuracy. Minuteman I started with an accuracy of 2 km, but now Minuteman III is said to have an accuracy of 120 meters. The Peacekeeper (MX) missile, no longer in service, is said to have an accuracy of 40 meters. You can use a much, much smaller warhead if you're 40 meters away compared to 2 kilometers.

mannyv• 2 years ago

In general, the USSR had bigger bombs because they weren't as accurate as US bombs. So yes.

jonathanyc3• 2 years ago

I also could not believe inertial navigation systems worked as well as they do when I first learned about them. At some point in time the most sophisticated IMUs were actually export-controlled!

Maybe this has changed or is ineffective now that smartphone/quadcopter IMUs have caught up.

jandrewrogers• 2 years ago

Advanced IMUs are still export controlled and the state-of-the-art is classified. The US military considers this a cornerstone technology and has invested heavily in R&D over the years. The IMUs that are widely available commercially have improved significantly over the years but so have the military versions.

krisoft4• 2 years ago

Maybe this has changed or is ineffective now that smartphone/quadcopter IMUs have caught up.

They did not caught up. There are two kind of IMUs: one where you have to account for the rotation of the Earth during signal processing and one where there is no point because it will be lost in the noise anyway. The smartphone/quadcoptee IMUs are the second kind. The first kind is still export controlled.

rcxdude2• 2 years ago

consumer-grade IMUs are still well below the performance of even much older military-grade IMUs (which tend to be impressive feats of precision engineering with pricetags to match, but also physically much larger). You'll still find anything that's useful for working out position over any time period is export-controlled (dual-use or stricter).

benjam475• 2 years ago

It is how Apollo navigated, although both the ground (via ground tracking) as well as the crew (via locating stars through a extant, and the Apollo computer having a database of the position of several dozen bright stars) could update their current position throughout the flight.

embedded_hiker• 2 years ago

Apollo used star sightings to check the accuracy of the gyros that measured which way the spacecraft was pointed. The stars could not be used to determine position like a ship at sea could do.

Besides inertial navigation, they had a transponder that would echo back a continuous pseudorandom bit stream, and the delay gave a precise measurement of distance.

bigiain• 2 years ago

The errors would be less of a problem than Apollo's, when your longest possible flight is only 45 minutes or so. And I'm not sure, but I guess the ballistic portion of the flight is uncontrolled (since the steering is from the rocket motors), so perhaps only the first few minutes are all it needs to maintain accuracy for?

beerandt10• 2 years ago

I said it downthread, but GPS is even more absurd. And we take it for granted.

But it's based on the same idea, only getting position as a derivative of velocity. (And some borderline-magic statistics applied.)

And that's before taking into account the absurdity of how low power the broadcast signal is.

CamperBob24• 2 years ago

GPS doesn't work that way. It uses instantaneous time-of-flight computation.

KK7NIL7• 2 years ago

surely all the little errors compound?

Random errors (i.e. noise) cancel out in the long run thanks to integration. You're then only left with systematic offset errors which can presumably be calibrated out to a large extent.

petermcneeley• 2 years ago

Really depends on what you mean by random. If it is truly random then you will end up with a random walk.

https://en.wikipedia.org/wiki/Random_walk

jfoutz• 2 years ago

When the MacBook got the acceleration sensor, I hacked up a little program to estimate velocity, and a button to reset at stoplights. Some friends drove me around, it worked poorly. it did pretty ok on the highway, but awful in the city.

I think if I kept messing with it, it'd get a lot better, but I sorta lost interest. This was more of a fun weekend toy.

I think all phones have them, and they might be reachable through chrome/safari. And it is kinda fun to play with, but you'll probably hit sampling rate errors pretty quick. you gotta guess the shape of the curve between datapoints.

ghaff3• 2 years ago

At least modern ICBMs do a star sight to calibrate at the top of their trajectory but, yes, that’s what inertial guidance is. Draper Labs basically pioneered.

jojobas3• 2 years ago

It's far from the top of their trajectory (by then the warheads are long separated), and only submarine-launched missiles need it.

kevin_thibedeau• 2 years ago

That is how all self-guided weapons systems worked before GPS was viable. Many still retain that capability as a fallback. Notably, the Tomahawks fired during Desert Storm had to transit over Iranian airspace because they needed the mountainous terrain to correct for their inertial drift before turning toward their targets over the flat Iraqi plains.

https://en.wikipedia.org/wiki/TERCOM

lupusreal• 2 years ago

Almost all. Walleye television-guided glide bombs used edge detection on a television signal to aim themselves in. A human would designate a target at the start but then the bomb would autonomously track the target. An optical fire-and-forget system developed in the 1960s.

Sidewinders are another example. Both developed at China Lake.

flavius29663• 2 years ago

before GPS was viable

GPS can be jammed (see Russia-UKraine war), so inertial systems are still very important for rockets, for example some HIMARS rockets start with GPS and then rely only on inertial while getting close to target.

dingaling• 2 years ago

The little errors do compound, but the errors have been made progressively littler; a modern ring-laser gyro INS has a drift of one millidegree per hour or less.

Or you can add an external correcting factor, such the Trident's astronav system that takes star-shots to recalibrate the INS.

ddalex• 2 years ago

When Nintendo Wii motes first appeared, they were some of the few devices at the time with cheap MESM accelerometers and gyroscopes that were programmer-friendly.

I remember taping two together back to back and integrating acceleration across them. That's when I learned Kalman filters. It was accurate enough so I could throw it across my desk and measure the desk length :)

djmips• 2 years ago

Kalman filters were also used in the AGC - useful for landing on the moon. I suspect they were not used by the Minuteman - does anyone know?

https://en.wikipedia.org/wiki/Kalman_filter#History

https://github.com/chrislgarry/Apollo-11/blob/master/Luminar...

JR1427• 2 years ago

See https://news.ycombinator.com/item?id=40692333

rjsw• 2 years ago

Operation Black Buck [1] used inertial navigation.

[1] https://en.wikipedia.org/wiki/Operation_Black_Buck

spoonfeeder0064• 2 years ago

Interesting tech and all, but ultimately efforts like this are a waste. If we humans could instead get over our self-perceived need to engage in warfare for childish reasons then we could dedicate such efforts to more productive things like helping homeless people get housing and skills, or developing better psychological sciences to help drug addicts get free from their disease of addiction, you name it

O SON OF SPIRIT! The best beloved of all things in My sight is Justice; turn not away therefrom if thou desirest Me, and neglect it not that I may confide in thee. By its aid thou shalt see with thine own eyes and not through the eyes of others, and shalt know of thine own knowledge and not through the knowledge of thy neighbor. Ponder this in thy heart; how it behooveth thee to be. Verily justice is My gift to thee and the sign of My loving-kindness. Set it then before thine eyes. > ~ Baha'i Teaching

CamperBob24• 2 years ago

It would be great if we could all share that sentiment. But ask the Ukrainians how unilateral disarmament worked out for them. Unfortunately, it seems that this particular waste of resources and intellect is still necessary.

spoonfeeder0064• 2 years ago

Sorry, I don't mean anything against legitimate self defense, I'm talking rather about "self-perceived need to engage in warfare for childish reasons"

Examples of that would include ego, greed, petty revenge, etc...

But I guess the way I said it did come across that way, so yeah, my bad

I'm just saying that if we could evolve past such petty ego-based sentiments in the world, then wouldn't such pressure to develop weaponry in such massive amounts, and hence we could focus on actually making a functioning society

spoonfeeder0064• 2 years ago

O rulers of the earth! Be reconciled among yourselves, that ye may need no more armaments save in a measure to safeguard your territories and dominions. Beware lest ye disregard the counsel of the All-Knowing, the Faithful.
Be united, O kings of the earth, for thereby will the tempest of discord be stilled amongst you, and your peoples find rest, if ye be of them that comprehend. Should any one among you take up arms against another, rise ye all against him, for this is naught but manifest justice.
(“Gleanings from the Writings of Bahá’u’lláh”, pp. 253-254)

ThinkBeat3• 2 years ago

How did you reprogram the destination on the missiles?

kens20• 2 years ago

It depends. For Minuteman I, the missile needed to be physically rotated in the silo to be aligned with the target. Then the "Targeting Van" connected to the missile, downloaded the new targeting data to the disk, and checked that the guidance system was aligned. As for the targeting data, it was generated by a mainframe that determined the right trajectory and produced the optimized navigation polynomials that the targeting algorithm used. It was something like 740 words of data per target so only two targets could fit in the computer.

Minuteman III used a smarter targeting algorithm that only needed 70 words of data per target, so the missile could support something like 8 targets at once, selected by a knob on the launch console. (The launch officers didn't know what the targets were; they were just told to use target #3 for example.) The targeting data was read off punched tape for Minuteman II and a magnetic tape cartridge for Minuteman III.

beerandt10• 2 years ago

It was organized primarily via wargame scenarios, such that one target group comprised targets for a given scenario.

Simplified launch orders via the football, etc.

One group scenario might have been silo coordinates for an offensive first-strike. One group city coordinates for launch on warning strategic counter-strike, etc.

Each missile got a target from each scenario list programmed into a 'memory slot' with some overlap.

The organization/ optimization is mind-boggling.

But few understand that this is WHY the wargames and strikes had to be pre-planned ahead of time. It wasn't political hubris, but a technical requirement due to memory allocation.

ThinkBeat3• 2 years ago

One of the great things about chemical propulsion rockets is that they can take off with little to no prep at all. Ready to go at the press of a button.

The scary thing is that, when left alone for a long time, and these rockets have been, "the plates" keeping the chemicals from meeting each other ahead of schedule, corrodes, just a tiny bit at a time. each time raising the possibility of premature ejaculation just a tiny little fraction.

kens20• 2 years ago

I think you're talking about the Titan missiles, which use hypergolic propellants. The Minuteman missiles are solid fuel, so there are no separated chemicals.

beerandt10• 2 years ago

There are separated chemicals, the hypergolic means no ignition source required.

Which to his point would be even more scary, but just isn't the actual real world risk with the way the things were designed.

Plus hypergolics are usually toxic on their own, even without mixing and/or booming, in a quieter, more-deadly-to-technicians way.

Spills and defueling and meeting well-intentioned but bad safety guidelines that require abundant fiddling were the real source of danger. More fiddling == bad.

Iirc, the fuels/oxidizers/reagents/ whatever-liquids mainly behaved like aluminum oxidizing, such that reaction with the tanks components actually created an increased buffer layer of oxidation/ protection.

Tank corrosion wasn't high on the list of risks after it was figured out on a per-chemical basis.

I think it's one of the aspects covered fairly well in (the great, often posted) Ignition! [0]

[0]https://archive.org/details/ignition_201612

ThinkBeat3• 2 years ago

A cheerful thought is that according to atomic scientists the world is closer to nuclear holocaust now, than we have ever been.

The future so bright, I gotta wear shades.

https://thebulletin.org/doomsday-clock/current-time/

IamTC• 2 years ago

I believe parts of the subsea industry uses a similar concept, i.e., gyroscope based for inertial navigation.

Obtaining position & veocity: I think it even more interesting when one compares the difficulties of getting these fundamental navigation data in an aerial, ground and undersea platforms.

aussieguy1234• 2 years ago

So. The world could be blown up with just 8kb of memory. No need for a killer AI with hundreds of GB's of vram.

artemonster• 2 years ago

A testament to human ingenuity and genius, work of art even. The machined parts, the crude electronics, all of it

LarsDu88• 2 years ago

So much discrete circuitry and now any bum can get the same performance from a 15 year arduino

N_A_T_E• 2 years ago

Wow, so this thing needs to be pointed directly at the target 8,000 miles away and will miss the target by the amount of error in aim.

"To target a Minuteman I missile, the missile had to be physically rotated in the silo to be aligned with the target, an angle called the launch azimuth. This angle had to be extremely precise, since even a tiny angle error will be greatly magnified over the missile's journey. " ... "The guidance platform was completely redesigned for Minuteman II and III, eliminating the time-consuming alignment that Minuteman I required. The new platform had an alignment block with rotating mirrors. Instead of rotating the missile, the autocollimator remained fixed in the East position and the mirror (and thus the stable platform) was rotated to the desired launch azimuth. "

ianbicking• 2 years ago

I noticed that too. That seemed odd at first read... after all, it has a guidance system, it's not relying on exact aim. I'm assuming it's more that its guidance system can only has so much fuel at its disposal and ability to correct errors, and if it's aimed incorrectly it would exhaust its fuel before it corrects its trajectory.

ethbr15• 2 years ago

Sometimes it's less work to engineer a hard problem into an easy one, than to solve the hard problem.

Most of the tech for the Minuteman I was developed in the mid-1950s.

With that level of processing, would you rather solve a 2d problem by precisely orienting the missile before launch? Or a 3d one by requiring it to orient during flight?

Keep in mind: any equipment to self-orient in-flight also needs to be carried on the missile itself, while being tolerant of launch, acceleration, and reentry forces.

Any precision machinery at the launch site has no such requirements.

ecshafer• 2 years ago

Shooting a projectile, accounting for the earths rotation and wind, is essentially a solved problem (with computers). So I don't think this is that outlandish and I imagine it gets pretty accurate. Creating an analytical solution by hand is a junior level physics problem.

kens20• 2 years ago

There are two factors. First, any missile with inertial guidance needs to have a precise angle reference as a basis for the guidance system. If the guidance system starts off slightly wrong about which way is North, it's going to miss the target. Second, the guidance system in Minuteman I could only turn about 10 degrees from its initial angle before the wires would get tangled up. The solution in Minuteman I was to use the launch azimuth as the reference angle, so it was precisely lined up against this angle. Most of the alignment was physically rotating the missile, but the last bit of alignment was by constantly rotating the stable platform for alignment with the light beam from the autocollimator.

datavirtue• 2 years ago

Purely a deterrent. No one in their right mind would try to launch these expecting them to hit their target.

somat• 2 years ago

There is a well written video essay on the inner workings of the d-17 computer used on the minuteman 1

Minuteman D-17b: The Desktop Computer Was Born in an ICBM

https://www.youtube.com/watch?v=MJPnZzZtswc (Alexander the ok)

mrguyorama4• 2 years ago

This is Youtuber has had several very well researched and thorough videos about topics that readers of Ken would enjoy, including Buran, the F-14 Air data computer, Elite, and the birth of Digital fly by wire out of the Apollo program.

Check him out and give him slack for his vocal fry. It's mildly annoying but the content is just so good.

The guidance system and computer of the Minuteman III nuclear missile

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