Missile Defense Alarm System
The Missile Defense Alarm System, or MIDAS, was a United States Air Force Air Defense Command system of 12 early-warning satellites that provided limited notice of Soviet intercontinental ballistic missile launches between 1960 and 1966. Originally it was intended to serve as a complete early-warning system working in conjunction with the Ballistic Missile Early Warning System.
Source: Wikipedia — Missile Defense Alarm System (CC BY-SA 4.0)