spy satellite

satellite used for espionage

A spy satellite (officially referred to as a reconnaissance satellite) is an Earth observation satellite or communications satellite deployed for military or intelligence applications. The first generation type (i.e. Corona   and Zenit) took photographs then ejected canisters of photographic film, which would descend to earth. Corona capsules were retrieved in mid-air as they floated down on parachutes. Later spacecraft had digital imaging systems and downloaded the images via radio links.
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Noun
1. a satellite with sensors to detect nuclear explosions
(hypernym) satellite, artificial satellite, orbiter