Going down the captain pedant conversation path here, but technically all satellites also need to burn energy to stay in orbit or will eventually fall. The only ones who don’t have achieved escape velocity

No, they don’t. In the absence of drag, which only the lowest satellites have, they just stay up there forever. The fuel is needed for orbit changes and correcting drift due to gravitational instabilities.

And all the dragless satellites around the earth are focusing on documenting as all the frictionless spherical cows on the earth

Are any of them truly free of drag? Like, are there 0 molecules of atmosphere at some height, or just entirely negligible amounts of atmosphere for all practical purposes?

None. In theory there are parts of space that are a true vacuum but not everywhere, and definitely not near planetary bodies.

There's a reason our satellites need station-keeping fuel. https://en.wikipedia.org/wiki/Orbital_station-keeping

Even in deep space there are something like two atoms per cubic meter just "there". But atmospheric density drops exponentially with altitude.

Yeah anything above about ~1000km or so is essentially zero drag.

It adds up. Also, Kessler syndrome potential is not negligible.

Kessler syndrome is important but somewhat unrelated.

Beyond LEO the drag is really negligible in the sense that other factors (e.g. gravitational abnormalities, the moon) have larger effects.

IANAP ("I am not a physicist"), but any two objects in orbit around their common center of gravity are slowly radiating energy into space in the form of gravity waves. This is why LIGO reports its chirps. Of course, this isn't very much energy, but given enough time all should orbits collapse.

I am a physicist. The gravitational energy loss from planet + satellite scale orbiting bodies is so small as to be orders of magnitude less than, say, the influence of gravitational anomalies like the Himalayas, or the tidal pull of the Moon.

To further add some (maybe helpful) pedantry, the boundary between an airplane and a satellite is usually taken to be the point at which the velocity required to remain aloft via aerodynamic lift exceeds the orbital velocity if there were no atmosphere.

This thread is like that meme/joke where a programmer's code gets more and less elaborate for a basic Hello World as their career advances.

Reminds me of this old classic: https://github.com/EnterpriseQualityCoding/FizzBuzzEnterpris...

> The only [satellites] who don’t have [to expend energy to stay in orbit] achieved escape velocity

... and are therefore no longer satellites. https://www.nasa.gov/audience/forstudents/5-8/features/nasa-... https://www.nasa.gov/audience/forstudents/5-8/features/nasa-...

Some Lagrange points are stable and therefore will not decay toward the Earth outside of other factors. (Because these systems are never sufficiently isolated, in the eternal view, therefore, also still require energy, though much, much less.) Though, of course, an object at a Lagrange point may still not technically be a satellite of earth. https://solarsystem.nasa.gov/faq/88/what-are-lagrange-points (though by the NASA definition above I'd argue that they are)

Lagrange points L1,2,3 are metastable and all are also perturbed by all the reality of not being result of two point masses in perfect vacuum.

Satellites also need to use some energy otherwise their orbit will eventually [0] bring them into atmosphere

[0]: https://en.wikipedia.org/wiki/Orbital_decay

We're all sitting in a curvature of space time, man. -_-