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"depending on atmospheric conditions" is a big IF in the polar regions. A USAF U-2 on a high altitude polar air sampling mission accidentally wandered into Sov

"depending on atmospheric conditions" is a big IF in the polar regions. A USAF U-2 on a high altitude polar air sampling mission accidentally wandered into Soviet airspace at the height of the Cuban missile crisis because auroras blocked the pilot's stellar fixes. See: http://www.vanityfair.com/politics/features/2008/06/missile_crisis_excerpt200806 http://www.vanityfair.com/politics/features/2008/06/missile_...

toomuchtodo 12y ago
Have we come far enough yet with mapping the earths magnetic field that you could use it to cross check your location with the star tracker's data?
- TTPrograms 12y ago
  It's extremely variable, and I assume unpredictable.
  - nitrogen 12y ago
    I seem to recall reading about magnetic field charts for aviation purposes, but their purpose was to translate from location to magnetic field orientation, not the other direction. https://upload.wikimedia.org/wikipedia/commons/2/28/Mv-world.jpg https://upload.wikimedia.org/wikipedia/commons/2/28/Mv-world... from https://en.wikipedia.org/wiki/Magnetic_declination https://en.wikipedia.org/wiki/Magnetic_declination
- ufmace 12y ago
  Sort of. I know a little about this from working in the oilfield. If you think navigating in the sky is tricky, try navigating underground. We had the BGGM[1], a model of the Earth's magnetic field, that gives us magnetic field strength and direction, given lat/long, altitude, and date. Accuracy was around 0.5deg in direction and I think 0.5% in strength. I'm not sure about the validity of it at more exotic locations and high altitudes, though. We used it as an accuracy check when taking field measurements to determine direction. I can elaborate if anybody's interested. As for using the data to check aircraft location, if the model is reasonable valid in those conditions, it might work as a sanity check. I doubt it would be practical to reverse it and get location from field information, though. It's already tough to get really good field data in an environment filled with metal objects and electric currents, though. [1] http://www.geomag.bgs.ac.uk/data_service/directionaldrilling/bggm.html http://www.geomag.bgs.ac.uk/data_service/directionaldrilling...

toomuchtodo 12y ago

Have we come far enough yet with mapping the earths magnetic field that you could use it to cross check your location with the star tracker's data?

TTPrograms 12y ago
It's extremely variable, and I assume unpredictable.
- nitrogen 12y ago
  I seem to recall reading about magnetic field charts for aviation purposes, but their purpose was to translate from location to magnetic field orientation, not the other direction. https://upload.wikimedia.org/wikipedia/commons/2/28/Mv-world.jpg https://upload.wikimedia.org/wikipedia/commons/2/28/Mv-world... from https://en.wikipedia.org/wiki/Magnetic_declination https://en.wikipedia.org/wiki/Magnetic_declination
ufmace 12y ago
Sort of. I know a little about this from working in the oilfield. If you think navigating in the sky is tricky, try navigating underground. We had the BGGM[1], a model of the Earth's magnetic field, that gives us magnetic field strength and direction, given lat/long, altitude, and date. Accuracy was around 0.5deg in direction and I think 0.5% in strength. I'm not sure about the validity of it at more exotic locations and high altitudes, though. We used it as an accuracy check when taking field measurements to determine direction. I can elaborate if anybody's interested. As for using the data to check aircraft location, if the model is reasonable valid in those conditions, it might work as a sanity check. I doubt it would be practical to reverse it and get location from field information, though. It's already tough to get really good field data in an environment filled with metal objects and electric currents, though. [1] http://www.geomag.bgs.ac.uk/data_service/directionaldrilling/bggm.html http://www.geomag.bgs.ac.uk/data_service/directionaldrilling...