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To risk being pedantic, US SLBMs (Tridents) indeed use stellar updates for their inertial guidance system. Our ICBMs have no update mechanism at all. Once they

To risk being pedantic, US SLBMs (Tridents) indeed use stellar updates for their inertial guidance system. Our ICBMs have no update mechanism at all. Once they're out of the silo, they're completely on their own.

HPsquared 2y ago
ICBMs would be more confident in their starting position and orientation. SLBMs would necessarily have more uncertainty in the initial conditions.
- varispeed 2y ago
  You can create nuclear load so powerful it won't matter where it hits.
  - m4rtink 2y ago
    Teller, is that you ?
  - red-iron-pine 2y ago
    "close only matters in horseshoes and nuclear strikes"
BurningFrog 2y ago
The BM part means "Ballistic Missile", which sounds like they're basically "thrown" into a parabolic path towards their target, like a falling rock. Or am I over-interpreting the name?
- gghffguhvc 2y ago
  Have a read of how MERV part of some ICBMs works. Lots going on as far as targeting goes. Also take a look at Trident 2 which can use GPS for course correction but isn’t reliant on it.
- dreamcompiler 2y ago
  That's exactly the right interpretation. You chuck them into space and after the rocket quits, Isaac Newton takes over. Contrast hypervelocity weapons, which -- contrary to the name -- don't really go faster but they can maneuver in the atmosphere at that speed.
beardedmoose 2y ago
The missile knows where it is at all times. It knows this because it knows where it isn't. By subtracting where it is from where it isn't, or where it isn't from where it is (whichever is greater), it obtains a difference, or deviation. The guidance subsystem uses deviations to generate corrective commands to drive the missile from a position where it is to a position where it isn't, and arriving at a position where it wasn't, it now is. Consequently, the position where it is, is now the position that it wasn't, and it follows that the position that it was, is now the position that it isn't. In the event that the position that it is in is not the position that it wasn't, the system has acquired a variation, the variation being the difference between where the missile is, and where it wasn't. If variation is considered to be a significant factor, it too may be corrected by the GEA. However, the missile must also know where it was. The missile guidance computer scenario works as follows. Because a variation has modified some of the information the missile has obtained, it is not sure just where it is. However, it is sure where it isn't, within reason, and it knows where it was. It now subtracts where it should be from where it wasn't, or vice-versa, and by differentiating this from the algebraic sum of where it shouldn't be, and where it was, it is able to obtain the deviation and its variation, which is called error.
- bagels 2y ago
  Why is this meme always pasted in to threads about missile guidance?
  - michaelsbradley 2y ago
    Because it’s a classic gag, even if it’s out of place on HN https://youtu.be/bZe5J8SVCYQ?feature=shared https://youtu.be/bZe5J8SVCYQ?feature=shared
    - debugnik 2y ago
      Not just an online gag, that's related to an excerpt of an alleged December 1997 issue of "Association of Air Force Missileers" on the GLCM Guidance System. Likely submitted in jest. https://web.archive.org/web/20050514035446/http://www.afmissileers.org/newsletters/NL1997/Dec97.pdf https://web.archive.org/web/20050514035446/http://www.afmiss...

HPsquared 2y ago

ICBMs would be more confident in their starting position and orientation. SLBMs would necessarily have more uncertainty in the initial conditions.

varispeed 2y ago
You can create nuclear load so powerful it won't matter where it hits.
- m4rtink 2y ago
  Teller, is that you ?
- red-iron-pine 2y ago
  "close only matters in horseshoes and nuclear strikes"

BurningFrog 2y ago

The BM part means "Ballistic Missile", which sounds like they're basically "thrown" into a parabolic path towards their target, like a falling rock. Or am I over-interpreting the name?

gghffguhvc 2y ago
Have a read of how MERV part of some ICBMs works. Lots going on as far as targeting goes. Also take a look at Trident 2 which can use GPS for course correction but isn’t reliant on it.
dreamcompiler 2y ago
That's exactly the right interpretation. You chuck them into space and after the rocket quits, Isaac Newton takes over. Contrast hypervelocity weapons, which -- contrary to the name -- don't really go faster but they can maneuver in the atmosphere at that speed.

beardedmoose 2y ago

The missile knows where it is at all times. It knows this because it knows where it isn't. By subtracting where it is from where it isn't, or where it isn't from where it is (whichever is greater), it obtains a difference, or deviation. The guidance subsystem uses deviations to generate corrective commands to drive the missile from a position where it is to a position where it isn't, and arriving at a position where it wasn't, it now is. Consequently, the position where it is, is now the position that it wasn't, and it follows that the position that it was, is now the position that it isn't. In the event that the position that it is in is not the position that it wasn't, the system has acquired a variation, the variation being the difference between where the missile is, and where it wasn't. If variation is considered to be a significant factor, it too may be corrected by the GEA. However, the missile must also know where it was. The missile guidance computer scenario works as follows. Because a variation has modified some of the information the missile has obtained, it is not sure just where it is. However, it is sure where it isn't, within reason, and it knows where it was. It now subtracts where it should be from where it wasn't, or vice-versa, and by differentiating this from the algebraic sum of where it shouldn't be, and where it was, it is able to obtain the deviation and its variation, which is called error.

bagels 2y ago
Why is this meme always pasted in to threads about missile guidance?
- michaelsbradley 2y ago
  Because it’s a classic gag, even if it’s out of place on HN https://youtu.be/bZe5J8SVCYQ?feature=shared https://youtu.be/bZe5J8SVCYQ?feature=shared
  - debugnik 2y ago
    Not just an online gag, that's related to an excerpt of an alleged December 1997 issue of "Association of Air Force Missileers" on the GLCM Guidance System. Likely submitted in jest. https://web.archive.org/web/20050514035446/http://www.afmissileers.org/newsletters/NL1997/Dec97.pdf https://web.archive.org/web/20050514035446/http://www.afmiss...