3 ms·

Aren't missiles launched from the surface, enabling a quick calibration just before launch? When there aren't clear skies to see stars, what other sort of non-

Aren't missiles launched from the surface, enabling a quick calibration just before launch? When there aren't clear skies to see stars, what other sort of non-GPS calibration could be done at sea?

rkagerer 4y ago
TIL submarines can fire ballistic missiles while submerged. It helps them maintain stealth. Here's a video from the 60's showing Polaris firings: https://en.m.wikipedia.org/wiki/File:1960-07-21_First_Polaris_Firing_By_Submerged_U-Boat.ogv https://en.m.wikipedia.org/wiki/File:1960-07-21_First_Polari...
cwillu 4y ago
Among others (Tomahawk being notable), https://en.wikipedia.org/wiki/UGM-27_Polaris https://en.wikipedia.org/wiki/UGM-27_Polaris was designed to be launched underwater, in service from 1961.
deleted 4y ago
[deleted]
baybal2 4y ago
psychphysic 4y ago
Not always, but we I understand it even a wire periscope can provide excellent location data. AFAIK submarine launched ballistic missiles aren't launched that far below the water surface and even a traditional periscope can reach 15+m
krisoft 4y ago
> When there aren't clear skies to see stars, what other sort of non-GPS calibration could be done at sea? It is speculated that you could keep navigational errors bounded with gravimetric measurements. Essentially if you have a detailed pre-surveyed map of the underwater landscape, and high precision gravity measurements you can match your measurements to the undulations of the expected gravity field. Somewhat similar, at least on the math level, to how TERCOM works with cruise missiles.
- HPsquared 4y ago
  Wouldn't the movement of the boat cause too much "noise" for these kinds of measurements? How would they cancel out small movements due to e.g water currents?
  - krisoft 4y ago
    The short and true answer is that if I would know for sure I could not write about here. Hence all of this is speculation. Very likely they would use the best motion isolation money can buy. Also the submarine is quite slow (especially at navigation speeds) so the terrain changes under it slowly. Water currents and the motion of people and machinary happens at much higher rate, so you can probably try to eliminate the quick changes and keep the slower changes with filtering and statistics.
  - ISL 4y ago
    It isn't as hard as you might think. Most gravity-gradient measurements are differential. Common-mode accelerations can be substantially-rejected. Also, if you're in the precision-measurement game, navigationally-relevant signals can be much larger than the precision of modern instruments. People in the prospecting business sometimes fly gravity-gradiometers in airplanes.
MayeulC 4y ago
During the day, you can use the sun position as a reference (like it's done using a sextan). You only need an accurate clock, and can determine the sun's location through the clouds. I suppose you can also do it with the moon. On a dark, cloudy night though? You could risk using the sonar since the launch is going to make a ruckus anyway. Compare measures against seafloor maps.
- izacus 4y ago
  Boomers aren't supposed to surface for their missile launches for half a century now, it's just too dangerous.
- deleted 4y ago
  [deleted]
jasonwatkinspdx 4y ago
Nope, they're launched from just a bit below the surface to make it harder to spot and chase the sub via aircraft/helicopter. Here's footage: https://www.youtube.com/watch?v=ppz_jj2uw7k&t=25s https://www.youtube.com/watch?v=ppz_jj2uw7k&t=25s Pre GPS navigation methods include sextants, celestial navigation, and LORAN (navigation via bearings to multiple radio towers). Sub launch ballistic missiles actually have an automated version of celestial navigation: there's a star spotting camera that compares what it sees to a reference database of the couple hundred brightest stars. So even if the missile starts out with a lot of ambiguity about where it's launched from, by the time it gets above the clouds it can correct this.
- amelius 4y ago
  The missile could still use GPS to correct its trajectory ...
  - nradov 4y ago
    Yes, as long as the GPS (Navstar) satellites haven't been vaporized...
nradov 4y ago
Ballistic missile submarines are primarily second-strike weapons. By the time they launch, our GPS satellites might already be destroyed by anti-satellite weapons. So far no one has demonstrated a working weapon that can knock out satellites in medium orbit (like the Navstar constellation) but I have to assume that China will have such a capability soon. For routine operations, modern subs do carry a towed buoy which can be used to exchange radio messages and update GPS position while the sub remains deep underwater. This carries some risk of detection, but less than coming up to periscope depth.
- somenameforme 4y ago
  I'm failing to see the difference on the medium orbital range? It's still "just" an intercept. I assumed all tests were done at low orbits to help ensure the junk deorbits as quickly as possible while still fulfilling 100% proof of effect, but that is just an assumption and I'd certainly be curious to know if/why/how I was wrong!
  - nradov 4y ago
    The basic physics are the same regardless of altitude, but the launchers used in current known ASAT weapons systems are only capable of reaching LEO. Need a bigger booster. I assume the US / China / Russia have secret programs working on this right now.

Aren't missiles launched from the surface, enabling a quick calibration just before launch? When there aren't clear skies to see stars, what other sort of non-GPS calibration could be done at sea?

rkagerer 4y ago

TIL submarines can fire ballistic missiles while submerged. It helps them maintain stealth. Here's a video from the 60's showing Polaris firings: https://en.m.wikipedia.org/wiki/File:1960-07-21_First_Polaris_Firing_By_Submerged_U-Boat.ogv https://en.m.wikipedia.org/wiki/File:1960-07-21_First_Polari...

cwillu 4y ago

Among others (Tomahawk being notable), https://en.wikipedia.org/wiki/UGM-27_Polaris https://en.wikipedia.org/wiki/UGM-27_Polaris was designed to be launched underwater, in service from 1961.

deleted 4y ago

[deleted]

baybal2 4y ago

psychphysic 4y ago

Not always, but we I understand it even a wire periscope can provide excellent location data. AFAIK submarine launched ballistic missiles aren't launched that far below the water surface and even a traditional periscope can reach 15+m

krisoft 4y ago

> When there aren't clear skies to see stars, what other sort of non-GPS calibration could be done at sea? It is speculated that you could keep navigational errors bounded with gravimetric measurements. Essentially if you have a detailed pre-surveyed map of the underwater landscape, and high precision gravity measurements you can match your measurements to the undulations of the expected gravity field. Somewhat similar, at least on the math level, to how TERCOM works with cruise missiles.

HPsquared 4y ago
Wouldn't the movement of the boat cause too much "noise" for these kinds of measurements? How would they cancel out small movements due to e.g water currents?
- krisoft 4y ago
  The short and true answer is that if I would know for sure I could not write about here. Hence all of this is speculation. Very likely they would use the best motion isolation money can buy. Also the submarine is quite slow (especially at navigation speeds) so the terrain changes under it slowly. Water currents and the motion of people and machinary happens at much higher rate, so you can probably try to eliminate the quick changes and keep the slower changes with filtering and statistics.
- ISL 4y ago
  It isn't as hard as you might think. Most gravity-gradient measurements are differential. Common-mode accelerations can be substantially-rejected. Also, if you're in the precision-measurement game, navigationally-relevant signals can be much larger than the precision of modern instruments. People in the prospecting business sometimes fly gravity-gradiometers in airplanes.

MayeulC 4y ago

During the day, you can use the sun position as a reference (like it's done using a sextan). You only need an accurate clock, and can determine the sun's location through the clouds. I suppose you can also do it with the moon. On a dark, cloudy night though? You could risk using the sonar since the launch is going to make a ruckus anyway. Compare measures against seafloor maps.

izacus 4y ago
Boomers aren't supposed to surface for their missile launches for half a century now, it's just too dangerous.
deleted 4y ago
[deleted]

jasonwatkinspdx 4y ago

Nope, they're launched from just a bit below the surface to make it harder to spot and chase the sub via aircraft/helicopter. Here's footage: https://www.youtube.com/watch?v=ppz_jj2uw7k&t=25s https://www.youtube.com/watch?v=ppz_jj2uw7k&t=25s Pre GPS navigation methods include sextants, celestial navigation, and LORAN (navigation via bearings to multiple radio towers). Sub launch ballistic missiles actually have an automated version of celestial navigation: there's a star spotting camera that compares what it sees to a reference database of the couple hundred brightest stars. So even if the missile starts out with a lot of ambiguity about where it's launched from, by the time it gets above the clouds it can correct this.

amelius 4y ago
The missile could still use GPS to correct its trajectory ...
- nradov 4y ago
  Yes, as long as the GPS (Navstar) satellites haven't been vaporized...

nradov 4y ago

Ballistic missile submarines are primarily second-strike weapons. By the time they launch, our GPS satellites might already be destroyed by anti-satellite weapons. So far no one has demonstrated a working weapon that can knock out satellites in medium orbit (like the Navstar constellation) but I have to assume that China will have such a capability soon. For routine operations, modern subs do carry a towed buoy which can be used to exchange radio messages and update GPS position while the sub remains deep underwater. This carries some risk of detection, but less than coming up to periscope depth.

somenameforme 4y ago
I'm failing to see the difference on the medium orbital range? It's still "just" an intercept. I assumed all tests were done at low orbits to help ensure the junk deorbits as quickly as possible while still fulfilling 100% proof of effect, but that is just an assumption and I'd certainly be curious to know if/why/how I was wrong!
- nradov 4y ago
  The basic physics are the same regardless of altitude, but the launchers used in current known ASAT weapons systems are only capable of reaching LEO. Need a bigger booster. I assume the US / China / Russia have secret programs working on this right now.