8 ms·

FYI the 24 GPS satellites are all in Low Earth Orbit. Well within the reach of missile technology today. These will be taken out within minutes of the next war.

FYI the 24 GPS satellites are all in Low Earth Orbit. Well within the reach of missile technology today. These will be taken out within minutes of the next war. This is why the Naval Academy as of 2 years ago teaches navigation by sextant. Was in the Army as late as 2013, and they (at least that unit) almost never let us use GPS during training (only USGS maps, protractors and compass) for this reason.

DaiPlusPlus 8y ago
There’s also astral navigation (how did automatic AN computers work in the 1970s/1980s anyway? CCD and mememy tech was far more primitive, so I really want to know the technical details) - and ground-based radio beacons.
- justinator 8y ago
  I mean, did they work at all? GPS was around in the 70's/80's, just not in any way that was useful for civilian purposes.
- RyJones 8y ago
  The SR71 had impressive AN computers. Here is where you might start [0] looking. I found some lessons online [1] that might help. [0] https://timeandnavigation.si.edu/multimedia-asset/nortronics-nas-14v2-astroinertial-navigation-system https://timeandnavigation.si.edu/multimedia-asset/nortronics... [1] https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=2ahUKEwjd_9zl7rvcAhWbIjQIHSSJCFQQFjAAegQIBxAC&url=http%3A%2F%2Ffer3.com%2Farc%2Fimgx%2Fmalkin-accuracy-of-astro-nav.pdf&usg=AOvVaw0VR5di0SMKMZ5tV0tCOK-q https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&c...
- j9461701 8y ago
  Automated celestial navigation is actually surprisingly old technology, first being pioneered in the 1950s on the snark missile. Of course at first it was extremely unreliable, with the snark flying off target so often the part of the ocean the missiles were being tested in was humorously dubbed "snark infested waters" due to all the off target missiles that sunk there. But eventually people got better and did amazing things with relatively primitive tools, and by the '60s decently successful guidance systems using the stars were common place on ICBMS. As to technical details, here is a write up of the NAS26 astro-inertial guidance system from the '70s: http://www.dtic.mil/dtic/tr/fulltext/u2/a090649.pdf http://www.dtic.mil/dtic/tr/fulltext/u2/a090649.pdf The navy and the air force get all the coolest toys, I tell you what.
Analemma_ 8y ago
There are 33 GPS satellites, and they are in a medium orbit, not LEO. Which is not to say they are invulnerable, but compared to jamming or spoofing, I think the satellites themselves are considered one of the less likely points of failure (or attack) of the system.
- alain_gilbert 8y ago
  I'm just curious what people think about this imaginary scenario. Let say an opponent already have satellites in space with laser weapons, could they just destroy the GPS satellites using such a tech ? Or do you guys think that this technology does not exists ? We saw some videos in recent years of NASA laser weapons taking down planes. That's why I'm thinking about this. Maybe the distance in space would make it impossible... I have no clue.
  - speeq 8y ago
    Pure speculation but I think the X37-B spacecraft is probably some sort of satellite jammer / destroyer and possibly a refuel / service ship.
    - azernik 8y ago
      Probably not. Its design features are: 1. Long-duration flight (low-single-digit years). 2. In very small numbers (at most one in orbit at a time). 3. Recoverability of payload. 4. Very high delta-V (i.e. can shift orbits a lot, and has been observed doing so in big jumps during deployments). The most likely guess is a testbed for military satellite subsystems; put a camera or a radar on there, and you can get a feel for its performance at different altitudes/angles, and also bring the prototypes back down to do a teardown after the fact.
  - rhcom2 8y ago
    It would still has line of sight to deal with so you would either need a bunch of them or some type of maneuverability. It would be easier to just shoot a rocket it at. https://en.wikipedia.org/wiki/Anti-satellite_weapon https://en.wikipedia.org/wiki/Anti-satellite_weapon
lloda 8y ago
~22000 km is far above LEO.
deleted 8y ago
[deleted]
starpilot 8y ago
~let's have kiki~
saagarjha 8y ago
The GPS satellites have a period of half a day. This puts them in MEO.
justinator 8y ago
Once all the GPS (or similar) satellites are knocked out, uh, what are you going to use now fight the war? On either side? And anyways, what country has the budget to knock out twenty four satellites in quick succession? And what if this doesn't work? I'm having a hard time thinking the US Gov. doesn't have a shadow GPS constellation up there, somewhere, but I will concede this is the most wahoo part of my meanderings... I think knocking out GPS is a rather risky move to even try.
- dingo_bat 8y ago
  > And anyways, what country has the budget to knock out twenty four satellites in quick succession? China and USA. Any war that they don't participate in is anyway irrelevant on the global scene.
- lobotryas 8y ago
  What country? Russia or China. They don't have to take them all out at once. Just the threat of the system going sown at any time is enough to make it unreliant.
  - justinator 8y ago
    Think of the threat to the US GPS system. To make it stick, you need to knock out most of the GPS system, as well as the system of the US allies (EU) and if you do that, you're in hot water with those allies. I say, good luck with that, sir. I think 24 missiles pointed at earth targets would have more impact than some pesky satellites.
    - rohit89 8y ago
      > as well as the system of the US allies (EU) and if you do that, you're in hot water with those allies. You will already be in a lot of hot water if you're in a war with the US. The countries who have the capability of doing this have thousands of missiles. A hundred of them being used to knock out some sats is nothing.
ridgeguy 8y ago
>FYI the 24 GPS satellites are all in Low Earth Orbit. No, they're not. LEO is an orbital period of 128 minutes or less, which for circular orbits is ~1200 miles or less [1]. GPS satellites are in 12 hour orbits ( see "Orbital Characteristics" in [1], putting them at a little more than 12,500 miles out [2]. And anyway, a satellite's altitude has little to do with how soft a target it might be. It's not simple. That said, I'm glad training emphasizes non-GPS modalities. You never can tell when Carrington will come calling [3]. [1] https://en.wikipedia.org/wiki/Low_Earth_orbit https://en.wikipedia.org/wiki/Low_Earth_orbit [2] https://en.wikipedia.org/wiki/Global_Positioning_System https://en.wikipedia.org/wiki/Global_Positioning_System [3] https://en.wikipedia.org/wiki/Solar_storm_of_1859 https://en.wikipedia.org/wiki/Solar_storm_of_1859
- azernik 8y ago
  For those knowing not so much about orbital mechanics - that's about halfway to geostationary (orbit radius (semi-major axis, technically) is directly proportional to period, and GEO has by definition a 24-hour period).

DaiPlusPlus 8y ago

There’s also astral navigation (how did automatic AN computers work in the 1970s/1980s anyway? CCD and mememy tech was far more primitive, so I really want to know the technical details) - and ground-based radio beacons.

justinator 8y ago
I mean, did they work at all? GPS was around in the 70's/80's, just not in any way that was useful for civilian purposes.
RyJones 8y ago
The SR71 had impressive AN computers. Here is where you might start [0] looking. I found some lessons online [1] that might help. [0] https://timeandnavigation.si.edu/multimedia-asset/nortronics-nas-14v2-astroinertial-navigation-system https://timeandnavigation.si.edu/multimedia-asset/nortronics... [1] https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=2ahUKEwjd_9zl7rvcAhWbIjQIHSSJCFQQFjAAegQIBxAC&url=http%3A%2F%2Ffer3.com%2Farc%2Fimgx%2Fmalkin-accuracy-of-astro-nav.pdf&usg=AOvVaw0VR5di0SMKMZ5tV0tCOK-q https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&c...
j9461701 8y ago
Automated celestial navigation is actually surprisingly old technology, first being pioneered in the 1950s on the snark missile. Of course at first it was extremely unreliable, with the snark flying off target so often the part of the ocean the missiles were being tested in was humorously dubbed "snark infested waters" due to all the off target missiles that sunk there. But eventually people got better and did amazing things with relatively primitive tools, and by the '60s decently successful guidance systems using the stars were common place on ICBMS. As to technical details, here is a write up of the NAS26 astro-inertial guidance system from the '70s: http://www.dtic.mil/dtic/tr/fulltext/u2/a090649.pdf http://www.dtic.mil/dtic/tr/fulltext/u2/a090649.pdf The navy and the air force get all the coolest toys, I tell you what.

Analemma_ 8y ago

There are 33 GPS satellites, and they are in a medium orbit, not LEO. Which is not to say they are invulnerable, but compared to jamming or spoofing, I think the satellites themselves are considered one of the less likely points of failure (or attack) of the system.

alain_gilbert 8y ago
I'm just curious what people think about this imaginary scenario. Let say an opponent already have satellites in space with laser weapons, could they just destroy the GPS satellites using such a tech ? Or do you guys think that this technology does not exists ? We saw some videos in recent years of NASA laser weapons taking down planes. That's why I'm thinking about this. Maybe the distance in space would make it impossible... I have no clue.
- speeq 8y ago
  Pure speculation but I think the X37-B spacecraft is probably some sort of satellite jammer / destroyer and possibly a refuel / service ship.
  - azernik 8y ago
    Probably not. Its design features are: 1. Long-duration flight (low-single-digit years). 2. In very small numbers (at most one in orbit at a time). 3. Recoverability of payload. 4. Very high delta-V (i.e. can shift orbits a lot, and has been observed doing so in big jumps during deployments). The most likely guess is a testbed for military satellite subsystems; put a camera or a radar on there, and you can get a feel for its performance at different altitudes/angles, and also bring the prototypes back down to do a teardown after the fact.
- rhcom2 8y ago
  It would still has line of sight to deal with so you would either need a bunch of them or some type of maneuverability. It would be easier to just shoot a rocket it at. https://en.wikipedia.org/wiki/Anti-satellite_weapon https://en.wikipedia.org/wiki/Anti-satellite_weapon

lloda 8y ago

~22000 km is far above LEO.

deleted 8y ago

[deleted]

starpilot 8y ago

~let's have kiki~

saagarjha 8y ago

The GPS satellites have a period of half a day. This puts them in MEO.

justinator 8y ago

Once all the GPS (or similar) satellites are knocked out, uh, what are you going to use now fight the war? On either side? And anyways, what country has the budget to knock out twenty four satellites in quick succession? And what if this doesn't work? I'm having a hard time thinking the US Gov. doesn't have a shadow GPS constellation up there, somewhere, but I will concede this is the most wahoo part of my meanderings... I think knocking out GPS is a rather risky move to even try.

dingo_bat 8y ago
> And anyways, what country has the budget to knock out twenty four satellites in quick succession? China and USA. Any war that they don't participate in is anyway irrelevant on the global scene.
lobotryas 8y ago
What country? Russia or China. They don't have to take them all out at once. Just the threat of the system going sown at any time is enough to make it unreliant.
- justinator 8y ago
  Think of the threat to the US GPS system. To make it stick, you need to knock out most of the GPS system, as well as the system of the US allies (EU) and if you do that, you're in hot water with those allies. I say, good luck with that, sir. I think 24 missiles pointed at earth targets would have more impact than some pesky satellites.
  - rohit89 8y ago
    > as well as the system of the US allies (EU) and if you do that, you're in hot water with those allies. You will already be in a lot of hot water if you're in a war with the US. The countries who have the capability of doing this have thousands of missiles. A hundred of them being used to knock out some sats is nothing.

ridgeguy 8y ago

>FYI the 24 GPS satellites are all in Low Earth Orbit. No, they're not. LEO is an orbital period of 128 minutes or less, which for circular orbits is ~1200 miles or less [1]. GPS satellites are in 12 hour orbits ( see "Orbital Characteristics" in [1], putting them at a little more than 12,500 miles out [2]. And anyway, a satellite's altitude has little to do with how soft a target it might be. It's not simple. That said, I'm glad training emphasizes non-GPS modalities. You never can tell when Carrington will come calling [3]. [1] https://en.wikipedia.org/wiki/Low_Earth_orbit https://en.wikipedia.org/wiki/Low_Earth_orbit [2] https://en.wikipedia.org/wiki/Global_Positioning_System https://en.wikipedia.org/wiki/Global_Positioning_System [3] https://en.wikipedia.org/wiki/Solar_storm_of_1859 https://en.wikipedia.org/wiki/Solar_storm_of_1859

azernik 8y ago
For those knowing not so much about orbital mechanics - that's about halfway to geostationary (orbit radius (semi-major axis, technically) is directly proportional to period, and GEO has by definition a 24-hour period).