4 ms·

> Satellites can definitely do things, but they're not magical and people can track where they're looking and just... sail in a different direction I know noth

> Satellites can definitely do things, but they're not magical and people can track where they're looking and just... sail in a different direction I know nothing about this really, so forgive my ignorance. Assuming a carrier is found and tracked by a satellite in the ocean, how could it possibly escape the satellite's detection before being targeted by a drone or some other type of munition? If the ship starts sailing in a different direction, the people (or AI) tracking via satellite would notice and adjust, right?

foota 6mo ago
I don't believe parent is right, but satelites don't stay in one place unless they're on the equator, because otherwise they have to be moving. This means that you need many satelites to maintain coverage of a single spot. I don't know how many military satelites China has, but I would have assumed it would be sufficient to cover the pacific sufficiently to find an aircraft carrier. (the obvious caveat here being clouds, which are fairly common over the ocean)
- nerdsniper 6mo ago
  The JWST has a 6.5 meter mirror. The largest (known) spy satellites have a mirror of ~3m diameter. At GEO (geostationary orbit) that would provide an imaging resolution of about 7 meters. An aircraft carrier is about 337x76 meters. So from geostationary altitudes, a satellite similar to a KH-11 would see an American aircraft carrier as a blob of about 48 "pixels". This is probably enough signal to track all aircraft carriers around the globe in real time. It would have a field of view roughly the size of Houston (50x50 miles) and would have enough electricity from solar panels to power reaction wheels to stay pointed at carrier groups indefinitely. (~15-year lifespan would be limited by xenon supply for ion thrusters that keeps the satellite in GEO orbit)
  - nradov 6mo ago
    The Chinese Yaogan-41 satellite is in geostationary orbit and might have a mirror in the 4m range. https://www.csis.org/analysis/no-place-hide-look-chinas-geosynchronous-surveillance-capabilities https://www.csis.org/analysis/no-place-hide-look-chinas-geos...
  - wredcoll 6mo ago
    > It would have a field of view roughly the size of Houston (50x50 miles) Wait, what? Like, this is a whole bunch of extremely unreliable numbers being stacked on top of each other to reach an unsupported conclusion, but how is a 50 square mile field of view supposed to find something in the middle of the pacific?
    - joha4270 6mo ago
      The satellite moves, so every orbit it captures a globe spanning strip that is 50 miles wide (here uncritically accepting the 50 miles figure). And the carrier isn't going to be in the middle of the pacific, its going to want to launch strikes, so its going to be within (say 500 miles) of Chinese military targets, which does narrow down the size of the haystack somewhat. But yes, this is a significant challenge. On the modern battlefield it is usually significantly harder to find something than to kill something after you have found it.
    - nerdsniper 6mo ago
      You only need to find the aircraft carrier once (say, when it docks) and then the satellite can remain pointed at it forever.
      - wredcoll 6mo ago
        Correct me if I'm wrong, but satellites... orbit. They don't just fly in arbitrary directions following a target. Even something like a rain storm can lose visual track of a carrier group, or even just night time, at which point you've now got an increasingly large area to search again to find the carrier which can be anywhere inside a several hundred mile circle.
- nandomrumber 6mo ago
  > but satelites don't stay in one place What? > unless they're on the equator What? > because otherwise they have to be moving What?
  - foota 6mo ago
    It was admittedly a bit sloppy. The more accurate version (IANAKSPP, I am not a kerbal space program player) would be that the only way to maintain a satelite in one position (without expending an infeasible amount of energy) is to position it above the equator and sync its speed with the Earth's rotation, allowing it to stay in a single position above the Earth. Satelites always have to be moving fast enough such that the centripetal force is sufficient to counteract the Earth's gravitational pull, otherwise they would fall back onto the planet.
rawgabbit 6mo ago
I believe satellites are usually in an orbit. They can’t follow an carrier for example. The satellites may be in a constellation that can track the carrier. That is why anti-satellites weapons have been developed. E.g., a jet fighter flies straight up and then fires a long range missile. https://www.esa.int/Enabling_Support/Space_Transportation/Types_of_orbits https://www.esa.int/Enabling_Support/Space_Transportation/Ty... https://en.wikipedia.org/wiki/Anti-satellite_weapon https://en.wikipedia.org/wiki/Anti-satellite_weapon
- peterfirefly 6mo ago
  Do you think a carrier can very far in the couple of hours it takes for a satellite to orbit around the Earth?
  - nradov 6mo ago
    A carrier can likely get far enough to generate a miss. Missiles and drones have very limited sensors so in order to hit anything another platform has to cue them with a fairly precise target location. In other words, an adversary like China would need to have enough satellites, submarines, and/or patrol aircraft to maintain a continuous target track long enough to make a decision, launch the weapons, and have them fly out to the target. Current thinking is that China could probably do this inside the first island chain but would struggle to put the pieces together further out in the open Pacific Ocean.
  - rawgabbit 6mo ago
    My understanding is to track something like a carrier the satellite has to be in low earth orbit. Those circle the earth about every two hours. So it is not so much the carrier outruns the satellite; it is the satellite outruns the carrier. https://eos.com/blog/types-of-satellites/ https://eos.com/blog/types-of-satellites/
  - greedo 6mo ago
    If the carrier is aware of the overflight (and I assume the USN isn't run by complete idiots), it can adjust course after the overflight. And at 30 knots, can be 100s of miles away from its initial location when the satellite returns. Now satellite constellations make it harder, since their numbers limit this strategy. But currently, none of the know systems utilize SAR like the LEO satellites, so they wouldn't function well in bad weather. They'd have to rely on optics which can be severely degraded.
space_fountain 6mo ago
Some quick Googling implies China has satellites capable of tracking shipping via radar from geostationary orbit. I'm not really convinced that aircraft carriers can hide these days?
- Schiendelman 6mo ago
  Those satellites KNOW where the freighters are going, and check in every day on progress. They aren't looking for something that's intentionally sailing in an unpredictable direction (with no radio emissions in wartime).
  - space_fountain 6mo ago
    Why not? It's not exactly hard? The exact capabilities aren't public, but there are companies that provide daily synthetic radar captures for the whole globe and similarly companies that do this for imagery. It would take ages but I think you and I could both right an algorithm to classify if an image or high map has an aircraft carrier in it? Even if you can't get data for the whole globe taking a photo of a 10 mile of ocean every 10 minutes and shifting the center based on where a boat isn't hard. There aren't that many aircraft carriers. Aircraft carriers and tanks are both capable machines built and designed for a different environment than we have now. They can still be useful. Most countries don't have the ability to image the whole globe or lob weapons across an ocean, but I'm pretty skeptical they'd survive long in a war with say China
    - Schiendelman 6mo ago
      I understand you don't think it's hard. It's hard. I'm trying to provide information to help people here understand why. What you're proposing doesn't work. Are you interested in understanding why it doesn't work?
      - space_fountain 6mo ago
        Yes, I am interested in understanding why this is hard

foota 6mo ago

I don't believe parent is right, but satelites don't stay in one place unless they're on the equator, because otherwise they have to be moving. This means that you need many satelites to maintain coverage of a single spot. I don't know how many military satelites China has, but I would have assumed it would be sufficient to cover the pacific sufficiently to find an aircraft carrier. (the obvious caveat here being clouds, which are fairly common over the ocean)

nerdsniper 6mo ago
The JWST has a 6.5 meter mirror. The largest (known) spy satellites have a mirror of ~3m diameter. At GEO (geostationary orbit) that would provide an imaging resolution of about 7 meters. An aircraft carrier is about 337x76 meters. So from geostationary altitudes, a satellite similar to a KH-11 would see an American aircraft carrier as a blob of about 48 "pixels". This is probably enough signal to track all aircraft carriers around the globe in real time. It would have a field of view roughly the size of Houston (50x50 miles) and would have enough electricity from solar panels to power reaction wheels to stay pointed at carrier groups indefinitely. (~15-year lifespan would be limited by xenon supply for ion thrusters that keeps the satellite in GEO orbit)
- nradov 6mo ago
  The Chinese Yaogan-41 satellite is in geostationary orbit and might have a mirror in the 4m range. https://www.csis.org/analysis/no-place-hide-look-chinas-geosynchronous-surveillance-capabilities https://www.csis.org/analysis/no-place-hide-look-chinas-geos...
- wredcoll 6mo ago
  > It would have a field of view roughly the size of Houston (50x50 miles) Wait, what? Like, this is a whole bunch of extremely unreliable numbers being stacked on top of each other to reach an unsupported conclusion, but how is a 50 square mile field of view supposed to find something in the middle of the pacific?
  - joha4270 6mo ago
    The satellite moves, so every orbit it captures a globe spanning strip that is 50 miles wide (here uncritically accepting the 50 miles figure). And the carrier isn't going to be in the middle of the pacific, its going to want to launch strikes, so its going to be within (say 500 miles) of Chinese military targets, which does narrow down the size of the haystack somewhat. But yes, this is a significant challenge. On the modern battlefield it is usually significantly harder to find something than to kill something after you have found it.
  - nerdsniper 6mo ago
    You only need to find the aircraft carrier once (say, when it docks) and then the satellite can remain pointed at it forever.
    - wredcoll 6mo ago
      Correct me if I'm wrong, but satellites... orbit. They don't just fly in arbitrary directions following a target. Even something like a rain storm can lose visual track of a carrier group, or even just night time, at which point you've now got an increasingly large area to search again to find the carrier which can be anywhere inside a several hundred mile circle.
nandomrumber 6mo ago
> but satelites don't stay in one place What? > unless they're on the equator What? > because otherwise they have to be moving What?
- foota 6mo ago
  It was admittedly a bit sloppy. The more accurate version (IANAKSPP, I am not a kerbal space program player) would be that the only way to maintain a satelite in one position (without expending an infeasible amount of energy) is to position it above the equator and sync its speed with the Earth's rotation, allowing it to stay in a single position above the Earth. Satelites always have to be moving fast enough such that the centripetal force is sufficient to counteract the Earth's gravitational pull, otherwise they would fall back onto the planet.

rawgabbit 6mo ago

I believe satellites are usually in an orbit. They can’t follow an carrier for example. The satellites may be in a constellation that can track the carrier. That is why anti-satellites weapons have been developed. E.g., a jet fighter flies straight up and then fires a long range missile. https://www.esa.int/Enabling_Support/Space_Transportation/Types_of_orbits https://www.esa.int/Enabling_Support/Space_Transportation/Ty... https://en.wikipedia.org/wiki/Anti-satellite_weapon https://en.wikipedia.org/wiki/Anti-satellite_weapon

peterfirefly 6mo ago
Do you think a carrier can very far in the couple of hours it takes for a satellite to orbit around the Earth?
- nradov 6mo ago
  A carrier can likely get far enough to generate a miss. Missiles and drones have very limited sensors so in order to hit anything another platform has to cue them with a fairly precise target location. In other words, an adversary like China would need to have enough satellites, submarines, and/or patrol aircraft to maintain a continuous target track long enough to make a decision, launch the weapons, and have them fly out to the target. Current thinking is that China could probably do this inside the first island chain but would struggle to put the pieces together further out in the open Pacific Ocean.
- rawgabbit 6mo ago
  My understanding is to track something like a carrier the satellite has to be in low earth orbit. Those circle the earth about every two hours. So it is not so much the carrier outruns the satellite; it is the satellite outruns the carrier. https://eos.com/blog/types-of-satellites/ https://eos.com/blog/types-of-satellites/
- greedo 6mo ago
  If the carrier is aware of the overflight (and I assume the USN isn't run by complete idiots), it can adjust course after the overflight. And at 30 knots, can be 100s of miles away from its initial location when the satellite returns. Now satellite constellations make it harder, since their numbers limit this strategy. But currently, none of the know systems utilize SAR like the LEO satellites, so they wouldn't function well in bad weather. They'd have to rely on optics which can be severely degraded.

space_fountain 6mo ago

Some quick Googling implies China has satellites capable of tracking shipping via radar from geostationary orbit. I'm not really convinced that aircraft carriers can hide these days?

Schiendelman 6mo ago
Those satellites KNOW where the freighters are going, and check in every day on progress. They aren't looking for something that's intentionally sailing in an unpredictable direction (with no radio emissions in wartime).
- space_fountain 6mo ago
  Why not? It's not exactly hard? The exact capabilities aren't public, but there are companies that provide daily synthetic radar captures for the whole globe and similarly companies that do this for imagery. It would take ages but I think you and I could both right an algorithm to classify if an image or high map has an aircraft carrier in it? Even if you can't get data for the whole globe taking a photo of a 10 mile of ocean every 10 minutes and shifting the center based on where a boat isn't hard. There aren't that many aircraft carriers. Aircraft carriers and tanks are both capable machines built and designed for a different environment than we have now. They can still be useful. Most countries don't have the ability to image the whole globe or lob weapons across an ocean, but I'm pretty skeptical they'd survive long in a war with say China
  - Schiendelman 6mo ago
    I understand you don't think it's hard. It's hard. I'm trying to provide information to help people here understand why. What you're proposing doesn't work. Are you interested in understanding why it doesn't work?
    - space_fountain 6mo ago
      Yes, I am interested in understanding why this is hard