Its not only in space, but very far away from the Earth and the Moon, so it doesn't become saturated with IR. That apart, there is a lot of important IR a spy s

Its not only in space, but very far away from the Earth and the Moon, so it doesn't become saturated with IR. That apart, there is a lot of important IR a spy satellite would search for. The heat signature from a fighter jet is much larger that its visual signature, for example.