I don't think anything particularly detectable; they're so outweighed by the planet they're orbiting that the barycenter doesn't move measurably.
(To be clear, I'd imagine they're only doing the inspection thing right now, but I do suspect they're at least tinkering with on-orbit capture, refueling, disabling etc. with an arm.)
Maybe. The mass of an explosive could be pretty small compared to the mass of a satellite. And even if you do notice that your (secret military) satellite is slightly heavier than the spec says, what would you do about it?
How expensive is it to attach a couple of space-rated external cameras to a modern satellite? This wouldn’t eliminate the threat but it would certainly remove the uncertainty. Presumably once you recognized the threat, then defending against it couldn’t be the hardest problem to solve.
It would not need to be very big mine though would it? A grenade would probably be just fine to eliminate the satellite from being useful. Something that small means it could carry a lot of ammo
> A grenade would probably be just fine to eliminate the satellite from being useful
Sure, but if You are lucky or smart enough, to use it close enough.
For example Soviet satellite-interceptors spent few years and made few attempts (each time with bigger explosive), before achieve enough cloud density .
