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My father worked on the guidance system for the Trident nuclear missile at Singer-Kearfott for many years and this is mostly accurate. There was a lot of geometry involved.

They used to test launch the missiles back during the cold war from submarines off of California. The missile would cross the continental US and land in the water off Florida. The Soviets would invariably send "fishing" boats to measure the tests but the coast guard would never shoo them away -- they wanted the Soviets to know just how accurate these missiles were. And they were accurate.

It blows my mind what was possible with analog tech.

I find it highly inspiring.

I love analog tech, simple but generally insanely robust when done right.

It's not just analog tech: it's actual engineering. The hardware we have is amazing, most of our software royally sucks. But software done right is also most impressive.

To be fair, you can do a lot when you throw a near endless supply of money at things. Definitely impressive though.

To get great software, you need a small team and give them extremely clear requirements of what it should do with an assload of extremely clear testcases.

And lots of time to tune things and solve all little problems, and manually implement things when abstractions hamper performance.

This is a fairly generalizable rule in any engineering, unless you really are running the Apollo program (then when divide-and-conquering should probably remember this rule).

This is running into the no-code problem of clear-enough requirements being as complex as the code, via Kolmogorov.

The best software comes from a small team of top level devs who are also top level subject matter experts on the software’s domain. This doesn’t happen very often.

It doesn't have to be a small team. See "They Write The Right Stuff".

And even they make mistakes, software contains much more moving parts than hardware.

https://space.stackexchange.com/questions/37110/what-was-the...

Wow, thats a hell of a HN thing to say.

> Use of pointers required a written, approved, variance from the SW standards board. All the code was formally peer reviewed by at least 6 people. More complicated code would be reviewed by 20+ people - in the same room.

Do you think the "software engineering" people are giving engineering a bad name?

"Christian scientists" are Christians who attach themselves to the word science because science has such a powerful reputation. In their case I'm not worried about their trickery because everyone recognizes this. Everyone knows that Christian scientists are not scientists.

With software engineering it's not as clear. It's possible to create software applying engineering principles, but that's not what 99%+ of what is called "software engineering" is. And because most people don't recognize this, I think eventually this might run off "engineering".

In case you are wondering about all those “reading rooms” you may see in various cities:

Not to be confused with Christianity and science, Christians in Science, Christians in science and technology, or Scientology.

Christian Science is a set of beliefs and practices which are associated with members of the Church of Christ, Scientist. Adherents are commonly known as Christian Scientists or students of Christian Science, and the church is sometimes informally known as the Christian Science church. It was founded in 19th-century New England by Mary Baker Eddy, . . .

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

Software is engineering.

The near entire majority of software development in the modern world is digital plumbing. Very very few organizations practice software engineering

What's ur definition of "engineering" then

Yeah, I've worked in structural engineering with real chartered professional engineers. Most of that work was relying on rules of thumb and bodging in hacks to fit around too small customer budgets, changing requirements, contractors trying to exploit loopholes, or bad designs from architects. No job ever had the budget to do anything "properly".

Software development usually seems far more controlled than that was.

If you don't know what engineering means, why not check out Wikipedia?

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

I have my interpretation of "engineering" based on my degree, wiki's definition and discussions.

But people have various interpretations of that, especially those who try to act as if for some weird reasons software was not engineering and that's what I'm asking for.

Why so snarky?

You didn't read anything I wrote, did you?

I did and I think that I see the narration that's there.

As far as I’m aware test shots of both us Air Force and navy icbms off the west coast went to Kwajalein atoll.

Some other interesting details…

Naval icbms have star tracking for alignment and correction but land based ones do not.

The reasoning is that they are all dead reckoning…which requires knowing the initial location. The silo doesn’t move, but the subs do. Their location is tracked with another inertial guidance system but that adds error, so they use the star tracking.

Overall, the inertial navigation systems in modern icbms are not the limited in accuracy.

My favorite…there was a lot of pushback inside the us military on investing in increasing the accuracy of naval ICBMs. Doing so was seen as communicating/implying a shift in strategic goal from targeting cities (lower required accuracy) to targeting hardened facilities (higher required accuracy). That was seen as confrontational because sun based nuclear weapons had been generally treated as a second strike capability, but the primary reason to have the ability to target hardened facilities was for a first strike

From what I recall land missiles (minuteman) does its own alignment while in the silo to give it what it needs to hit that window in space where the RV detaches. There some documentation and YouTube videos depicting the alignment process.

Yup. But that’s based on knowing where the silo is, they are less mobile than subs (or trucks or trains). The alignment is all based on dead reckoning from where it started to where it’s going to know where it is, where it wants to be, and how to steer there.

> there was a lot of pushback inside the us military on investing in increasing the accuracy of naval ICBMs.

The book "Inventing Accuracy" covers this in detail. Fascinating historical perspective.

https://mitpress.mit.edu/9780262631471/inventing-accuracy/

This is the citation I should have provided and completely forgot to.

The most interesting boring book I’ve ever read.

So the confrontational is more because of the perceived shift to offensive ("unprovoked") first strike over "defensive" second strike, rather than any perceived loss of a deterrent second strike capability?

As I understood it yes. The ability to disarm the other side at will, and prevent any retaliation against cities, was seen as an more offensive capacity

Just want to note that the front page top 10 - 15 the last 24 hours or so has been disproportionately full of US government and military related posts. Something must be coming, some big news. BOLO

I'm recounting second hand so can't source anything but here is an SLBM test done in 2021 by a sub off of Florida, and it landed in the South Atlantic. So they must have several different ranges, and possibly it's changed over time.

https://missilethreat.csis.org/us-navy-test-fires-trident-ii...

They have a range in the Atlantic, it’s used for launches from the Atlantic…the French do similar things

https://www.thedrive.com/the-war-zone/34043/france-just-test...

Generally the logic is don’t launch on trajectories over land unless you have to. I believe all of the land based is ICBMs are still tested from vandenberg on the (most beautiful section of) California coast near Lompoc for the same reason. Vandenberg doesn’t have any deployed ICBMs, they all fly to kwaj for testing. Same reason nasa/spacex/seemingly everyone but China make it a goal to not have launches go over populated areas.

The guidance systems had to account for local variations in gravity as the missile flew to its target. One of the reasons ballistic missile accuracy improved so much was that measurements and mapping of these local anomalies improved so much.

Most are due to magma reservoirs or large mineral deposits. Some are well-known in their effect, but their specific cause is still unknown:

https://eos.org/science-updates/seismologists-search-for-the...

That's for Inertial Navigation Systems, they measure acceleration and from that integrate your position.

Other funny note…for all the Silicon Valley folk on HN…the trident missles the US uses on submarines are built in Sunnyvale.

I’m imaging most on here have read some/all of the secret history of Silicon Valley posts, but if you haven’t they are great

the "quartz crystals" were likely optical flats and they were connected by wringing-on (like a set of gauge blocks). https://en.wikipedia.org/wiki/Optical_flat#Wringing I'm not sure why you'd use an optical flat in a missle nav system, now I'm curious.

My guess would be for physical calibration of the INS gyroscope rotors?

https://navsource.org/archives/08/PolarisHistoryGEX1.htm (see bottom / appendix for examples of Polaris-era INS)

Given the CEP they were aiming for, and amount of time they had to fiddle with them, I'd guess they started very carefully with the physical precision of components.

CEP: Circular error of probable or probability.

The radius of a circle within which 50% of rounds will be found.

For the V-2 rocket this was 4.5 km.

For the Minuteman III missile, 240m.

Blast effects decrease with the cube of the radius, so a more accurate weapon means a smaller effective warhead. The "Flying Ginsu" AGM-114 Hellfire missile has a CEP of 5 meters or less, and uses blades rather than explosives to minimise any unintended casualties.

The Peacekeeper was even down to 90m.

But then withdrawn from service due to treaty, because with that accuracy, first striking your target's silos and hardened facilities starts to be a viable option.

Sometimes you can be too accurate.

Also, related, the W76-1/Mk4A height-adjusting fuze solved this this in a different way, by recognizing that there's a 3D kill-volume (above and around the target) rather than a 2D kill circle.

Consequently, if you aim beyond the target and have your warhead measure actual height vs expected once on a ballistic trajectory, you can adjust the fuzing height to detonate within the volume, even if you overshot the target. See figures 2 and 3. https://thebulletin.org/2017/03/how-us-nuclear-force-moderni...

Un/fortunately, this puts us back into viable first-strike territory.

That would be the AGM-114R9X. Most hellfire variants use explosive warheads.

Thanks. I was going off Wikipedia's designation, and don't know the full list of variants and their designations.

Would you know CEP for the 9X variant?

Based on pictures the CEP should be very small, centimeters maybe. This missile doesn't explode, instead it send 6 blades at the target. Pictures show direct hits.

I'm well aware, and that was my take, and I was initially going to write "within a metre", but couldn't find substantiation of that. The Hellfire itself offers the 5m value.

Cites on the Hellfire which I'd intended to include above:

<https://www.kabulpress.org/article89242.html>

<https://metinmediamath.wordpress.com/2013/10/10/missile-accu...>

Any window that a telescope is looking through will need to be optically flat, otherwise it will totally mess up the ability of the telescope to get a clear image.

I interned at the Charles Stark Draper Laboratory 20+ years ago. One of the guys was telling me at lunch about his work that day. He had to run some simulations to tell the Navy if their Trident guidance system needed to be sent back for re-manufacturing after a forklift operator dropped it. My understanding is that the handling crate had some kind of integral rough handling detector. (I presume calibrated weights on thin wires, in 3 axes, so you can bracket the peak accelerations by looking at which wires broke and which didn't.)

I was told that once above most of the atmosphere, the MIRV bus guidance unit pops the lens off and takes a snapshot of the stars. The MIRV bus is rotating at that point, so the telescope scans a good section of the sky, but it takes a snapshot at a very specific time and is only interested in a rather small patch of sky. It compares what it sees with a stored copy of what it should see, and uses that to re-calibrate the inertial measurement unit.

The way it was described to me was that one rotation checked the star field, the IMU was re-calibrated, the very next rotation was used to double-check the IMU calibration, and right after that, the MIRV bus started popping off the individual warheads. It seems strange to me that they would use such a short observation window to re-calibrate the IMU, rather than having a long period of continuous re-calibration. It's also highly possible that the guy explaining it to me was giving intentional misinformation to avoid accidentally disclosing TS/SCI to a non-cleared intern.

The nitty-gritty of guidance is fascinating. It's unfortunate that the main use cases for ultra-accurate guidance are in weapons.

There was a pendulous integrating gyroscopic accelerometer from the Apollo IMU sitting in a glass case in the lab... a shame given how few people were allowed into the lab.

Rough handling indicators are either glass vial based or contain a weight that slides into a window if sufficient force is exerted. There are plastic springs designed to break and other springs that force the weight to stay in the indication window.

An enthusiastic guy on youtube was trying to drop an egg from the edge of space and got shutdown for developing a terminal guidance system. So it's not so much about the only use being weapons, it's that weapons have state monopoly on precision guidance.

It's possible that he was describing the worst case scenario (minimal range shot), where they can't spend a lot of time up there.

There is much of a Chevaline, an upgrade to Polaris, in the Museum of Berkshire Aviation [1] which is near Reading, about 50 miles west of London. They also have some of the navigation systems, such as gyroscopes you can get a good look at.

I find the level of engineering fascinating, it's not often you get to see such detail close up.

I took a few photos[2] when visited about 10 years ago. Being a small museum it's quitehiggledy-piggledy but they also have a range of unusual exhibits such as a model of the Miles M.52 and a real Fairey Jet Gyrodyne.

[1] https://museumofberkshireaviation.co.uk/html/exhibits/cheval...

[2] https://www.flickr.com/photos/stevecargill/albums/7217772030...

>cylinders of ground quartz crystal, so flat ... their navigation worked by what you'd expect: Looking at the stars and comparing them to a super accurate timestamp, plus some core memory logarithmic tables or whatever

I didn't expect that, can someone explain? Sounds like some kind of dead reckoning system, I don't get why you need flat quartz discs to read the stars though?

Star trackers have been around for quite a while, so I'm not surprised! Even the Voyager probes had the ability to orient themselves relative to the Sun, Earth, and the star Canopus.