The person is simply saying you can. That’s it! As they said, it isn’t useful for things not near Earth. Perhaps not meaningless, but the “meaning” of the coordinate would decrease the further away from earth the object is.
If you’re saying it physically isn’t possible, then you’re basically saying the universe has some topological structure that cannot be projected onto the surface of a sphere. Which now that I’m thinking about it, is probably the case because of black holes? Lol maybe if the object is “in” a black hole then the coordinate actually is completely meaningless, but any other object would have some amount, even if low, of “meaning”
You're right that any 3D point can be mapped to a spherical coordinate system like GPS. I don’t disagree.
GPS coordinates are geodetic, tied to the WGS-84 ellipsoid and Earth’s rotating reference frame. They were designed for terrestrial navigation and near-Earth orbit, not for interplanetary space. Once you're dealing with the Moon, the Sun, or Lagrange points, you're so far outside the system's intended domain that projecting lat/lon/alt onto those locations introduces more confusion than clarity.
You're also right to point out that it's not physically impossible to describe a faraway object in that coordinate system.
There is just no practicable utility.
NASA and others use inertial frames, barycentric coordinates, and RA/Dec for a reason.
Also, love the black hole tangent - that’s where coordinate systems get seriously weird :-)
If you’re saying it physically isn’t possible, then you’re basically saying the universe has some topological structure that cannot be projected onto the surface of a sphere. Which now that I’m thinking about it, is probably the case because of black holes? Lol maybe if the object is “in” a black hole then the coordinate actually is completely meaningless, but any other object would have some amount, even if low, of “meaning”