True, but it also means that they will never (in any reasonable lifetime) have to be de-orbited because they are out of fuel.
Hmmm...... there is no practical way to de-orbit a satellite that high up, unless it had a lot of fuel drop the periapsis (lowest part of the orbit) from over 22,000 miles to 80-ish miles or less, to graze the atmosphere for a slow eventual orbital decay.
IIRC, what is sometimes done with a Goesynchronious satellite that still works but is at the end of its useful life, is to use the last bit of propellant to nudge it out of a perfect geosynchronous orbit.
Ah.... after typing the above I did a little bit of googling and found this gem. It explains the use of "graveyard orbits" for old Geosync satellites.
https://en.wikipedia.org/wiki/Graveyard_orbit
But anyway, you do make a great point on how long and useful these satellites should be without needing to rely on a limited amount of propellant to maintain their Geosync orbits.
BTW - the google search also found this pdf file that goes into more detail about decomissioning a geosync satellite. Simply reading page two provides a great amount of information.
https://digitalcommons.calpoly.edu/cgi/viewcontent.cgi?article=1036&context=aerosp
This reminds me a bit of a story I heard long ago, that I am 99% sure is real but a quick google search could not come up with it (Which could mean the story may be from 20 years or more since a lot of things are glaringly missing from the internet, or barely mentioned and hard to find, if they did not occur before the internet. Well the popular information age internet anyway). There was some satellite that was early into its mission, or at least in its prime, and a ground signal was accidentally sent to it, to turn the satellite "off". That signal was a mistake. Because it did not put it to sleep, it literally turned it OFF, FOREVER. There was no way for a new signal to re-activate the satellite to work, because the satellite was OFF, dead. So no receiver would ever be on to receive such a signal and no guidance was on to keep the antenna pointed toward Earth to even receive such a signal. Just a useless piece of junk the instant it responded to the "off" signal (not in an orbit the shuttle could ever get to, and probably not worth a shuttle launch even if it was). I do not recall if that was a Geosync satellite, a NASA interplanetary mission, or what. But a big lesson was learned by that. Many (if not all) satellites do need to have the capability to be turned "off" when they are no longer useful, but its not as easy a thing to do as it was when that accidental signal was sent.
- George Gassaway
