Magnetic north point moving fast

Discussion in 'Flight Following' started by Cluemeister, Jan 10, 2019.

  1. flyingcheesehead

    flyingcheesehead Touchdown! Greaser!

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    GPS satellites are not geosynchronous - If they were, you would always be receiving the same ones when you're in the same spot.

    As such, coverage IS global - I don't know where that map that @Dan Thomas posted came from.
     
  2. Tantalum

    Tantalum En-Route

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    Interesting, I thought I read somewhere that they were, and the map from Dan with the blank areas seemed to support that. But I stand corrected.. which raises the question, why would a "global" positioning system have blanks on it??

    *as a further tantalizing thought exercise, could spacecraft going to the moon theoretically map their location using the GPS satellites?

    *EDIT: I remember, INMARSAT has geostationary satellites, I learned that when I was closely following the MH370 saga..

    upload_2019-1-11_17-6-43.png
     
  3. Cap'n Jack

    Cap'n Jack Final Approach

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    I do question that map as I've had no problems with GPS in the part of India showing an area of "poor coverage" I'm also pretty sure Hawaii is in one of the depicted "poor coverage" zones as well, and I've had no issues there. Likewise, Cape Horn, the southern tip of South America gave me no trouble with GPS.
     
  4. Cap'n Jack

    Cap'n Jack Final Approach

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    Probably, for at least a while. I don't know how for out a spacecraft would go before there insufficient variation in reception times to calculate a good position. When there were fewer GPS satellites, sometimes the visible satellites would be in a geometry where there wasn't enough difference in timing to calculate a good solution.

    GPS works by measuring the time a signal is received, compared to the time it was sent. Knowing the speed of light, one can calculate a sphere of distance around each satellite. The spheres intersect at your location. Far enough away, the satellites appear to be close to one another in the sky, so there aren't really intersecting spheres, anymore. There is also a correction for relativity, and this would need to be adjusted for something moving away from the mass of the earth (http://www.astronomy.ohio-state.edu/~pogge/Ast162/Unit5/gps.html ).
     
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  5. Stephen Poole

    Stephen Poole Pre-Flight PoA Supporter

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    All true. The real problem, though, is that the transmitting antennas on the satellites are highly directional. I had to hunt for it (Google wants to show GPS receiving antennas), but from looking at the pattern on the Block IIF series, for example, the beam width is less than 20 degrees, focused on Earth. There would be very little signal radiated to the sides, and virtually none to the rear. Some low earth orbit satellites have used GPS, but I can't see it being used on a mission very far from Earth.

    This thread has already drifted away from the original Geomagnetic issue, but incidentally, I was astonished at how large those GPS satellites are -- thousands of pounds, with big honkin' flywheels for fine positioning!o_O
     
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  6. Eric Stoltz

    Eric Stoltz Pre-takeoff checklist

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    I shall validate your Earth science, for I am a geologist. You are correct. To really nerd out:. The sea floor rock, being ultra mafic, (high in Fe+) has crystals of Magnatite that align with the poles while they grow during the cooling process at the divergent zones in the rifts.
     
  7. Skyrys62

    Skyrys62 Pattern Altitude PoA Supporter

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    I also question this...
    It looks more like @Katamarino's "places I've been" map.


    [​IMG]
     
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  8. Katamarino

    Katamarino Cleared for Takeoff

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    Haha. We didn't have any trouble with GPS in that section of West Africa that's supposedly not covered!
     
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  9. Passenger

    Passenger Filing Flight Plan

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    The turtles are waking up - stuff 'bout to get real...
     
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  10. Piperonca

    Piperonca Pre-Flight

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    https://en.wikipedia.org/wiki/Turtles_all_the_way_down

    The following anecdote is told of William James. [...] After a lecture on cosmology and the structure of the solar system, James was accosted by a little old lady.

    "Your theory that the sun is the centre of the solar system, and the earth is a ball which rotates around it has a very convincing ring to it, Mr. James, but it's wrong. I've got a better theory," said the little old lady.

    "And what is that, madam?" inquired James politely.

    "That we live on a crust of earth which is on the back of a giant turtle."

    Not wishing to demolish this absurd little theory by bringing to bear the masses of scientific evidence he had at his command, James decided to gently dissuade his opponent by making her see some of the inadequacies of her position.

    "If your theory is correct, madam," he asked, "what does this turtle stand on?"

    "You're a very clever man, Mr. James, and that's a very good question," replied the little old lady, "but I have an answer to it. And it's this: The first turtle stands on the back of a second, far larger, turtle, who stands directly under him."

    "But what does this second turtle stand on?" persisted James patiently.

    To this, the little old lady crowed triumphantly,

    "It's no use, Mr. James — it's turtles all the way down."
     
  11. Stingray Don

    Stingray Don Pattern Altitude

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    But it is a flat turtle
     
  12. LongRoadBob

    LongRoadBob Line Up and Wait

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    As mentioned in another thread, GPS in northern Norway is being jammed by Russia. Also, criminals with cheap GPS jammers plugged into auto cogarette lighters have caused ambulance helicopters to lose GPS totally for some minutes.

    The jamming devices use are on the rise. Kind of alarming I’d the backups like compass start being unreliable.
     
  13. Skyrys62

    Skyrys62 Pattern Altitude PoA Supporter

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    In due time....yes..

    [​IMG]
     
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  14. BrianNC

    BrianNC Pattern Altitude

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    Here in Atlanta we have digital speed limit signs on I285 (not sure about 75 and 85), and they change depending on the traffic. Don't really need an LED screen per se.

    [​IMG]
     
  15. EppyGA

    EppyGA Touchdown! Greaser!

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    Only on 285 and they're just a suggestion ;)
     
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  16. Half Fast

    Half Fast En-Route

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    They post speeds on 285? I never noticed....
     
  17. Polarisguy

    Polarisguy Pre-Flight

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    Hope someone has alerted the Congress about this. Surely they can fix it with legislation. Always suspected one of our fearless leaders would pass a law requiring the sun to rise in the west, just to be equal


    Sent from my iPad using Tapatalk
     
  18. kath

    kath Line Up and Wait

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    GPS works just fine at the South Pole station in Antarctica.
    It can be used not just for position, but for keeping very precise time.
    Plenty o' satellites, not geosynchronous.

    Edit: there's an approach plate for the South Pole station, and it's a GPS approach.
     
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  19. Piperonca

    Piperonca Pre-Flight

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  20. Huckster79

    Huckster79 Pre-takeoff checklist

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    My cousin worked on the radio and navigational systems on the B52 until recently and he said it was just a few years ago they got rid of the sextant on board! Maybe they better go grab em back!

    For me once off flying on my own again, took a few year hiatus and am now getting my TW endorsement for my "new" plane, I plan on doing much of my traveling with paper maps and reading water towers- just because its fun and keeps you more engaged than flying the magenta line. I'm not saying I wont ever bring foreflight with me, but there is a time to read water towers and fly train tracks too. I find real enjoyment in doing things without all the tech aids... Well I guess thats why I purposefully bought a 40's era rig with no modern navigational updates. Though I'm hoping the compass keeps working-that would still be nice to use :)
     
  21. flyingcheesehead

    flyingcheesehead Touchdown! Greaser!

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    No problem. Just jump on him, kick him, run like hell after him, and jump before he bounces off anything.
     
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  22. Lantraxco

    Lantraxco Pre-Flight

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    Watch out for solar flares... mucks up the whole system....
     
  23. SoonerAviator

    SoonerAviator En-Route

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    upload_2019-1-17_8-36-54.jpeg
     
  24. bnt83

    bnt83 Final Approach

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    We need to invest huge sums of money into green tech because____________
     
  25. ripnet

    ripnet Pre-Flight

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    Wouldn't that be geostationary?

    I know GPS are neither
     
  26. geneseib

    geneseib Line Up and Wait

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    That. It's nearer true north than it has been for years. The horror of it all.
     
  27. flyingcheesehead

    flyingcheesehead Touchdown! Greaser!

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    Geostationary is when it doesn't appear to move at all, but I think most geosynchronous orbits would remain "visible" at all times as well.

    GPS satellites are halfway out, in a semi-synchronous orbit.
     
  28. mkosmo

    mkosmo Pattern Altitude PoA Supporter

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    Probably worth noting: The WAAS satellites are actually geostationary, but they're a bit special and not part of the GPS constellation. WAAS coverage is limited to a much smaller area, however.

    [​IMG]
     
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  29. flyingcheesehead

    flyingcheesehead Touchdown! Greaser!

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  30. Van Johnston

    Van Johnston Line Up and Wait

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    Semi-synchronous only means the period is one half; it doesn’t follow that they are half-way out. Semi-synchronous semi-major axis is ~ .63 the geosynchronous semi-major axis (cubed root of 1/4).
     
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  31. Spring Ford

    Spring Ford Pre-Flight

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  32. Polarisguy

    Polarisguy Pre-Flight

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    IFR = I follow roads


    Sent from my iPad using Tapatalk
     
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  33. flyingcheesehead

    flyingcheesehead Touchdown! Greaser!

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    Yep. XKCD is awesome. So many cartoons of the truth!
     
  34. ktup-flyer

    ktup-flyer En-Route

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    Imagine how confusing that would be...
     
  35. MooneyDriver78

    MooneyDriver78 Pattern Altitude

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    I think we would keep latitude N/S as is, and just renumber compasses. Is it legal to have a 180° correction?


    Tom