[ekianjo]

> extremely steady and predictable.

I don't agree with this claim, unless you quantify it. This has already been touched upon before, for example here:

> "It depends upon the orbit and what time scales you are talking about. Satellites are subjected to many perturbations in its orbit. There are effects due to atmospheric drag, which as you'd expect affect lower satellite orbits more than higher orbits, but the atmosphere swells up all the time depending upon the level of solar activity. Gravitationally, the Earth is not a point mass and it has regions where the gravity gradient changes, which causes the satellite to get pulled one way or another (very slightly) as it orbits around."

https://space.stackexchange.com/questions/31378/how-accurate...

[dwaltrip]

The link in the top-level comment addresses all of these concerns, among other considerations and carefully calibrated corrections. They clearly know what they are doing.

They have a high quality map of the variations of gravity across the surface of the Earth. They also have a model that accounts for atmospheric drag.

https://research.csiro.au/slrwavescoast/sea-level/measuremen...