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    Re: A little space navigation
    From: Peter Monta
    Date: 2018 Oct 4, 22:09 -0700

    Here ya go. Navigate with this image. Where are you?

    Interesting image.  There's no way it's from GEO because the sub-spacecraft point is too far north.  Earth-Sun L1 might be possible (DSCOVR), depending on the details of the orbit and the time of year; the Earth is showing significant phase, but maybe not so much as to rule out L1.  IGSO orbits can get as far north as you like, but no spacecraft come to mind that have cameras and are at this longitude.  More likely it's from a beyond-Earth-orbit mission, either on its initial escape trajectory or during a flyby (gravity assist).

    From the caption, we're to assume we're pretty close, no more than say ten Earth radii out, so that perspective comes into play.  One way forward is to pick a bunch of points on the limb and at land-sea boundaries and toss it at a brute-force max-likelihood search.  One potential problem is the camera parameters.  If there's any significant camera geometric distortion, that will look very similar to perspective distortion.  Also, it's not clear the camera axis is pointed straight down.  If this is a crop from the Falcon Heavy mission with the Tesla, then likely the camera axis is some distance from the Earth center, complicating the camera model.

    So an answer to the puzzle would supply 3D coordinates, (lat,lon,altitude), and uncertainties.  Altitude is likely to be a lot more uncertain.


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