7 ms·

I'm going to replay this from memory without googling it, just to keep the late 20th century air of some people swapping unverifiable facts in a pub: There was

by 13of40 3y ago

I'm going to replay this from memory without googling it, just to keep the late 20th century air of some people swapping unverifiable facts in a pub: There was an old friend of my mother's, now deceased, who was a retired engineer. He claimed to be the guy who invented the 2-part tuna can, and was known for handing out end chunks of titanium castings left over from some business he ran. At any rate, he had a couple of probably 8x4 inch (wide by high) cylinders of ground quartz crystal, so flat that you could put a drop of alcohol between them and they would be inseparable if you tried to pull them apart vertically. He claimed these were from the navigation system of Polaris nuclear missiles and 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 apologize of I've gotten any of this wrong, but he seemed legit, and again I have switched off Google for this one.

daniel-cussen 3y ago
[dead]
missedthecue 3y ago
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.
- ChatGTP 3y ago
  I find it highly inspiring. I love analog tech, simple but generally insanely robust when done right.
- jacquesm 3y ago
  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.
  - canadianfella 3y ago
    [dead]
  - PNewling 3y ago
    To be fair, you can do a lot when you throw a near endless supply of money at things. Definitely impressive though.
    - titzer 3y ago
      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.
      - sasaf5 3y ago
        And lots of time to tune things and solve all little problems, and manually implement things when abstractions hamper performance.
      - fsloth 3y ago
        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).
      - hoseja 3y ago
        This is running into the no-code problem of clear-enough requirements being as complex as the code, via Kolmogorov.
      - taneq 3y ago
        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.
- avs733 3y ago
  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
  - ceilingcat0 3y ago
    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.
    - avs733 3y ago
      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.
  - kijiki 3y ago
    > 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/ https://mitpress.mit.edu/9780262631471/inventing-accuracy/
- Full_Clark 3y ago
  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-indian-oceans-missing-mass https://eos.org/science-updates/seismologists-search-for-the...
  - 2rsf 3y ago
    That's for Inertial Navigation Systems, they measure acceleration and from that integrate your position.
- avs733 3y ago
  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
dekhn 3y ago
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 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.
- ethbr1 3y ago
  My guess would be for physical calibration of the INS gyroscope rotors? https://navsource.org/archives/08/PolarisHistoryGEX1.htm 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.
  - dredmorbius 3y ago
    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.
    - ethbr1 3y ago
      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-modernization-is-undermining-strategic-stability-the-burst-height-compensating-super-fuze/ https://thebulletin.org/2017/03/how-us-nuclear-force-moderni... Un/fortunately, this puts us back into viable first-strike territory.
inamberclad 3y ago
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.
KMag 3y ago
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.
- KennyBlanken 3y ago
  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.
- hoseja 3y ago
  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.
Steve44 3y ago
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/chevaline.htm https://museumofberkshireaviation.co.uk/html/exhibits/cheval... [2] https://www.flickr.com/photos/stevecargill/albums/72177720303989342 https://www.flickr.com/photos/stevecargill/albums/7217772030...
hammock 3y ago
>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?

by 13of40 3y ago

daniel-cussen 3y ago

[dead]

missedthecue 3y ago

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.

ChatGTP 3y ago
I find it highly inspiring. I love analog tech, simple but generally insanely robust when done right.
jacquesm 3y ago
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.
- canadianfella 3y ago
  [dead]
- PNewling 3y ago
  To be fair, you can do a lot when you throw a near endless supply of money at things. Definitely impressive though.
  - titzer 3y ago
    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.
    - sasaf5 3y ago
      And lots of time to tune things and solve all little problems, and manually implement things when abstractions hamper performance.
    - fsloth 3y ago
      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).
    - hoseja 3y ago
      This is running into the no-code problem of clear-enough requirements being as complex as the code, via Kolmogorov.
    - taneq 3y ago
      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.
avs733 3y ago
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
- ceilingcat0 3y ago
  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.
  - avs733 3y ago
    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.
- kijiki 3y ago
  > 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/ https://mitpress.mit.edu/9780262631471/inventing-accuracy/
Full_Clark 3y ago
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-indian-oceans-missing-mass https://eos.org/science-updates/seismologists-search-for-the...
- 2rsf 3y ago
  That's for Inertial Navigation Systems, they measure acceleration and from that integrate your position.
avs733 3y ago
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

dekhn 3y ago

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 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.

ethbr1 3y ago
My guess would be for physical calibration of the INS gyroscope rotors? https://navsource.org/archives/08/PolarisHistoryGEX1.htm 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.
- dredmorbius 3y ago
  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.
  - ethbr1 3y ago
    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-modernization-is-undermining-strategic-stability-the-burst-height-compensating-super-fuze/ https://thebulletin.org/2017/03/how-us-nuclear-force-moderni... Un/fortunately, this puts us back into viable first-strike territory.

inamberclad 3y ago

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.

KMag 3y ago

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.

KennyBlanken 3y ago
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.
hoseja 3y ago
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.

Steve44 3y ago

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/chevaline.htm https://museumofberkshireaviation.co.uk/html/exhibits/cheval... [2] https://www.flickr.com/photos/stevecargill/albums/72177720303989342 https://www.flickr.com/photos/stevecargill/albums/7217772030...

hammock 3y ago

>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?