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Consumer GPS devices have a speed and altitude limit [1], which I initially thought should preclude using it in a fighter jet, but I was wrong (only something e

Consumer GPS devices have a speed and altitude limit [1], which I initially thought should preclude using it in a fighter jet, but I was wrong (only something extreme like an SR-71 would hit this limit): > ...a limit placed on GPS tracking devices that disables tracking when the device calculates that it is moving faster than 1,000 knots (1,900 km/h; 1,200 mph) at an altitude higher than 18,000 m (59,000 ft).[3] This was intended to prevent the use of GPS in intercontinental ballistic missile-like applications. [1] https://en.wikipedia.org/wiki/Coordinating_Committee_for_Multilateral_Export_Controls#Legacy https://en.wikipedia.org/wiki/Coordinating_Committee_for_Mul...

LeoPanthera 7y ago
That makes sense - the limits are designed to stop you guiding a missile with one, not guiding a jet plane.
- tejtm 7y ago
  Unfortunately the safeguards can also kick in with high altitude balloons which have no speed beyond ambient wind.
  - someguydave 7y ago
    I doubt they hit the speed limit - but balloons can go up to 100,000 feet which is above the altitude limit.
  - an_account 7y ago
    The GPS has to shut off when going faster than a certain speed or higher than a certain altitude. IIRC the GPS maker can decided which they want to follow, and most chose to stop working at high altitude. It’s possible but more difficult to find a GPS that will work with high altitude balloons.
  - cstejerean 7y ago
    For everyone else that notices that COCOM limits require both speed and altitude, the problem is that some manufacturers have implemented these safeguards with an OR rather than an AND. So it’s possible to get tripped up by either limit in practice (unless you know for sure your specific device implements this as an and).
- CharlesColeman 7y ago
  >> > ...a limit placed on GPS tracking devices that disables tracking when the device calculates that it is moving faster than 1,000 knots (1,900 km/h; 1,200 mph) at an altitude higher than 18,000 m (59,000 ft).[3] This was intended to prevent the use of GPS in intercontinental ballistic missile-like applications. > That makes sense - the limits are designed to stop you guiding a missile with one, not guiding a jet plane. Only some kinds of missiles, though. It seems like those limits would be quite acceptable for cruise missile guidance, and I'd think GPS would be more useful there than in an ICBM.
  - cjhveal 7y ago
    Probably because the threat surface of a cruise missile is similar to a low-flying manned aircraft. There's lots of civilian use cases for GPS under those same conditions, where there's relatively fewer uses for speeds and altitudes in excess of the COCOM limits.
    - nojvek 7y ago
      I take it it’s much easier to get rid of cruise missile than ICBM? I just had a very dark thought suppose a nefarious entity got hold of starship, added a multi ton nuclear payload and sent it towards some city center. How does it get prevented?
      - nickthemagicman 7y ago
        Probably wouldn't even need a nuclear payload for that. If it was a sufficient size starship impacting at light speed I assume the impact would be tremendous.
      - cjhveal 7y ago
        The basic idea of missile defense is to intercept the incoming missile with another missile. What really matters is detection with enough time to react and fire those intercepting missiles. There are both cruise and ballistic missiles that can travel at hypersonic speeds which drastically reduce the viable interception window. Cruise missiles are actually scarier to modern militaries, in part because they are harder to detect separately from other aircraft.
- GhettoMaestro 7y ago
  It also is kinda misguided. If you have the capability to acquire/build a ballistic missile of that class, you most likely can (will) build your own GPS/GNSS receiver. Hell you can take a software defined radio and make your own software-based GPS receiver that does NOT disable itself at those described thresholds (some folks have done this for extremely high-altitude balloon experiments). Selling it of course is another question.
  - beerandt 7y ago
    People under-estimate how difficult geography/ geodesy/ navigation used to be, pre-NAVSTAR GPS. This difficulty was "built-in" to the military defensive posture/strategy/tactics of many countries, to the extent that simple possession of a GPS receiver was/is a crime. And not a misdemeanor, but a treason level offense. Keep in mind, the programs that evolved into NAVSTAR started in the 50s\60s and the tech specs were pretty much set by 1980, along with the legal framework and military policy regarding it's operation. Ironically, it was some of the systematic weaknesses if the original design that led to it being so much more useful (and accurate) than it was ever intended to be. But it is still a military program, with military style regulations, so it shouldn't be too surprised that some of the 1960's era rules haven't evolved too much. It's more surprising to me that so many of the restrictions have been relaxed. (Even if it's policy playing catch-up practice.)
  - jjeaff 7y ago
    Or even reverse engineer the firmware to remove the restriction. I'm also guessing that there are plenty of Chinese made gps devices that don't have that limitation. Simply because, why bother. Assuming you can find one accurate enough on AliExpress, I'd say there is a good chance it has no special restrictions.
    - conjectures 7y ago
      This is also what I would expect the reality of the situation to be, regardless of policy.
      - 7y ago
tzs 7y ago
An F-15 can exceed 59k feet and 1200 mph. It has a service ceiling of 65k feet, and a maximum speed of over 1600 mph.

LeoPanthera 7y ago

That makes sense - the limits are designed to stop you guiding a missile with one, not guiding a jet plane.

tejtm 7y ago
Unfortunately the safeguards can also kick in with high altitude balloons which have no speed beyond ambient wind.
- someguydave 7y ago
  I doubt they hit the speed limit - but balloons can go up to 100,000 feet which is above the altitude limit.
- an_account 7y ago
  The GPS has to shut off when going faster than a certain speed or higher than a certain altitude. IIRC the GPS maker can decided which they want to follow, and most chose to stop working at high altitude. It’s possible but more difficult to find a GPS that will work with high altitude balloons.
- cstejerean 7y ago
  For everyone else that notices that COCOM limits require both speed and altitude, the problem is that some manufacturers have implemented these safeguards with an OR rather than an AND. So it’s possible to get tripped up by either limit in practice (unless you know for sure your specific device implements this as an and).
CharlesColeman 7y ago
>> > ...a limit placed on GPS tracking devices that disables tracking when the device calculates that it is moving faster than 1,000 knots (1,900 km/h; 1,200 mph) at an altitude higher than 18,000 m (59,000 ft).[3] This was intended to prevent the use of GPS in intercontinental ballistic missile-like applications. > That makes sense - the limits are designed to stop you guiding a missile with one, not guiding a jet plane. Only some kinds of missiles, though. It seems like those limits would be quite acceptable for cruise missile guidance, and I'd think GPS would be more useful there than in an ICBM.
- cjhveal 7y ago
  Probably because the threat surface of a cruise missile is similar to a low-flying manned aircraft. There's lots of civilian use cases for GPS under those same conditions, where there's relatively fewer uses for speeds and altitudes in excess of the COCOM limits.
  - nojvek 7y ago
    I take it it’s much easier to get rid of cruise missile than ICBM? I just had a very dark thought suppose a nefarious entity got hold of starship, added a multi ton nuclear payload and sent it towards some city center. How does it get prevented?
    - nickthemagicman 7y ago
      Probably wouldn't even need a nuclear payload for that. If it was a sufficient size starship impacting at light speed I assume the impact would be tremendous.
    - cjhveal 7y ago
      The basic idea of missile defense is to intercept the incoming missile with another missile. What really matters is detection with enough time to react and fire those intercepting missiles. There are both cruise and ballistic missiles that can travel at hypersonic speeds which drastically reduce the viable interception window. Cruise missiles are actually scarier to modern militaries, in part because they are harder to detect separately from other aircraft.
GhettoMaestro 7y ago
It also is kinda misguided. If you have the capability to acquire/build a ballistic missile of that class, you most likely can (will) build your own GPS/GNSS receiver. Hell you can take a software defined radio and make your own software-based GPS receiver that does NOT disable itself at those described thresholds (some folks have done this for extremely high-altitude balloon experiments). Selling it of course is another question.
- beerandt 7y ago
  People under-estimate how difficult geography/ geodesy/ navigation used to be, pre-NAVSTAR GPS. This difficulty was "built-in" to the military defensive posture/strategy/tactics of many countries, to the extent that simple possession of a GPS receiver was/is a crime. And not a misdemeanor, but a treason level offense. Keep in mind, the programs that evolved into NAVSTAR started in the 50s\60s and the tech specs were pretty much set by 1980, along with the legal framework and military policy regarding it's operation. Ironically, it was some of the systematic weaknesses if the original design that led to it being so much more useful (and accurate) than it was ever intended to be. But it is still a military program, with military style regulations, so it shouldn't be too surprised that some of the 1960's era rules haven't evolved too much. It's more surprising to me that so many of the restrictions have been relaxed. (Even if it's policy playing catch-up practice.)
- jjeaff 7y ago
  Or even reverse engineer the firmware to remove the restriction. I'm also guessing that there are plenty of Chinese made gps devices that don't have that limitation. Simply because, why bother. Assuming you can find one accurate enough on AliExpress, I'd say there is a good chance it has no special restrictions.
  - conjectures 7y ago
    This is also what I would expect the reality of the situation to be, regardless of policy.
    - 7y ago

tzs 7y ago

An F-15 can exceed 59k feet and 1200 mph. It has a service ceiling of 65k feet, and a maximum speed of over 1600 mph.