For 56 years, U.S. military satellites watched the skies for the flash of a missile launch. That watch ended this month, when the Space Force retired the last two spacecraft of the Defense Support Program.
Both satellites flew a U.S. Space Command exercise in early September, rehearsing maneuvers across several orbits, then moved to a supersynchronous graveyard orbit, Combat Forces Command announced Oct. 1. The commander of Mission Delta 4, Col. Brandon Davenport, said the pair closed out a warning mission rooted in the Cold War.
The program’s first satellite reached geosynchronous orbit in 1970, tasked with spotting a Soviet missile launch and steadying a nuclear standoff. Later spacecraft tracked Scud launches in the 1991 Gulf War, and the same infrared sensors have doubled as wildfire and volcano watchers. Twenty-three DSP satellites flew in all. The last lifted off in 2007, only to drift off course a year later when a component failed.
A full-size test article sits in the National Museum of the United States Air Force in Ohio.
Its replacement, the Space-Based Infrared System, is already on station with six geosynchronous satellites and four in highly elliptical orbits. Lockheed Martin is finishing a pair of Next-Generation Overhead Persistent Infrared spacecraft for launch in the coming months; their sensors are built to pick out fainter signals.
Those two anchor a wider missile-warning architecture that spreads across orbits. Space Systems Command is planning a proliferated layer in medium Earth orbit, and the Space Development Agency is building one lower down. The Pentagon tried in its fiscal 2027 budget to end a polar Next-Gen OPIR effort, but lawmakers have kept it alive, leaving its fate to a final appropriations deal.
Mission Delta 4’s 2nd Space Warning Squadron will now shift to preparing that first Next-Gen OPIR launch and its early testing.
