Spaceflight

Le senseur stellaire is the star tracker, and the first word is a trap of a kind a dictionary rarely marks, because both entries are correct. The everyday French for a sensor is le capteur: un capteur de température, un capteur de pression, le capteur d’un appareil photo. That is the word used in a factory, in a car and in a laboratory, and it is built on capter, to pick something up — a signal, a station on the radio, somebody’s attention. Senseur is a straight borrowing of « sensor » and it survives in one field only: space and aeronautics, where le senseur solaire and le senseur stellaire are the settled terms. So the word that looks like the English one is not the general word but the narrow one, and writing it about a thermostat marks the writer as translating rather than speaking. The reverse slip is quieter and worth knowing too: capteur in a launch document would not be wrong, merely unidiomatic. Learn the pair together and let the subject choose between them.