I worked on a project that happened to have some spy satellite data as noise... You can hide them. A common practice is to do an orbital maneuver when the sate

I worked on a project that happened to have some spy satellite data as noise... You can hide them. A common practice is to do an orbital maneuver when the satellite is directly between the Sun-Earth line-of-sight, where attempts to use instruments are pretty well saturated/destroyed. With that said, it is still possible to see where the satellites go after such a boost if you are able to look really close to the limb of the sun with the right kind of equipment :)