An ultraviolet satellite was an orbital device that could emit ultraviolet light.
A constellation of 210 ultraviolet satellites was placed in a permanent 72-mile altitude, in orbit around Deneva in 2267 at the order of James T. Kirk. The light they emitted by burning tri-magnesite and trevium was powerful enough to reach through the planet's atmosphere to destroy an infestation of flying parasites. (TOS: "Operation -- Annihilate!")