>Also, it's impossible to hide a satellite in space. Every nation with a space program tracks every orbiting object that's even remotely big enough to be a functional artificial satellite. There are no "stealth" satellites, mostly because you can't hide a launch...

This isn't entirely true. First, satellites absolutely and do maneuver after launch, so they are not limited purely by the orbit they launch into. That is of course limited by how much propellant they carry onboard, but it is done (and for spy sats particularly). Second and more generally, for any object in space it's impossible to have persistent [0] omnidirectional stealth across all bands (due to thermodynamics). However, it's very much possible to have single band stealth (a shape that is radar stealth for example) as well as unidirectional multiband stealth, and because space is so big often that may be enough for a given scenario. For spy satellites in HEO they may as well be presenting a single side all the time to any Earth-based observers, and while some nations could react to that by launching tracking sats even farther the vast majority of actors (anyone on the level of ground-based amateur astronomers for sure) lack that capability. Transmission out can use the same idea, in space P2P laser links are generally invisible out of path, so a stealth sat could stealthily have comms to a non-stealth relay even further out.

As a practical matter right now it seems extremely doubtful any serious such systems are in place due to the huge hit on mission-effective mass which gets worse at distance, though it wouldn't be surprising if there have been some experiments at least. But with launch systems like Starship and enormously more mass to throw at problems, we may well see a certain number of much more serious stealth spy platforms eventually.

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0: In principle one could achieve perfect EM stealth temporarily by carrying onboard empty volume, a heat and a cold source (like a whole lot of liquid helium/nitrogen) then running as a closed system performing thermodynamic work averaging those out. Could run for some fixed period of time until the useful differential was exhausted and only be observable by interaction with mass in space or gravity. But who knows if that'll ever actually get utilized, since the unidirectional concept can be extended by an advanced space faring organization too. One can keep going farther and farther away from a target and compensate with a larger aperture with enough space capacity. If we imagine some aliens or something with an Earth observing stealth platform out in the Oort cloud say, it could be a kilometer across and very hot on the extrasolar facing side yet still damn near impossible for us to notice. Or of course someone could hide in the thermal noise of other sources. Interesting to speculate about from a hard scifi perspective anyway.