The US Space Force has retired the last two surviving Defense Support Program satellites, closing a missile-warning program that began in 1970. According to Ars Technica, the two satellites took part in an on-orbit maneuvering exercise in early September and then raised their orbits by a few hundred kilometers, a move typically used to dispose of spacecraft into graveyard orbits above geostationary space. The Space Force confirmed that the maneuver marked the program's official retirement.
The DSP constellation was one of the most important elements of American military space power during the Cold War. Each satellite carried thousands of infrared detectors and acted as a sensitive telescope in geosynchronous orbit, continuously monitoring the globe for missile launches. Initially built to detect Soviet ICBMs, the satellites later proved useful in conventional warfare, including detecting Iraqi Scud launches. US Space Force Col. Brandon Davenport called the constellation foundational, saying it ensured deterrence during the Cold War and protected deployed warfighters from the Gulf War until retirement.
The United States is not flying blind without DSP. The military began launching the Space Based Infrared System in 2011, and those satellites have better sensors that can detect dimmer events and provide longer warning times. The next step is the Next-Generation Overhead Persistent Infrared program, whose first satellite could launch within the next 12 months on a Vulcan rocket. The DSP program's long run spanned multiple launch vehicles, from Titan rockets to the Delta IV Heavy and even NASA's Space Shuttle.