In episode 11 of season 7 of TNG, the story takes place around the Argus Array, a subspace telescope reprogramed to observe several Federation sites: DS5, Starbase 47, the Iadara Colony, and the Utopia Planitia Shipyards. The problem with using this to spy is that
- Argus to DS5 = 28 ly
- Argus to Starbase 47 = 17 ly
- Argus to Iadara Colony = 5 ly
- Argus to Utopia Planitia (Mars) = 71 ly
Why would a hostile race use a telescope that gives data at least 5 years old?