Twins and GPS

[PeterDonis]

Satellite is almost immobile relative to the center of the Earth

No, it isn't. The 14,000 km/h speed that was given is relative to the center of the Earth.

differently to a point on the surface.

A point on the Earth's surface is moving, at most (for a point on the equator) at about 1600 km/h relative to the center of the Earth. So the satellite's speed relative to a point on the Earth's surface isn't that much different from its speed relative to the Earth's center.

But "There are no global inertial frames in curved space time."

But there are local ones, and as the reference to the Earth-Centered Inertial (ECI) frame should have told you, it is quite possible to treat a non-rotating frame centered on the Earth's center as inertial to a good enough approximation for many purposes, including the evaluation of the speeds of satellites.

You are hijacking someone else's thread with repeated incorrect comments that add nothing useful to the discussion. As a result, you have now been banned from further posting in this thread.