Re:China lands Chang'e-4 on far side of Moon
by Symmetry on Thursday January 03, 2019 @09:50AM
(#18815459)
It's a gravity saddle! From Earth's perspective it's a hill in the r direction but a well in the phi/theta directions. To orbit at a location always visible from Earth it needs to move in the phi/theta directions but moving the the r direction doesn't help, so it doesn't.
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Re:China lands Chang'e-4 on far side of Moon
by Latteland on Thursday January 03, 2019 @10:48AM
(#18815943)
And you clearly know this but i had to refresh my own knowledge of spherical coordinates - https://en.wikipedia.org/wiki/Spherical_coordinate_system