WashingtonThe US retired its last 2 Defense Support Program satellites.

They watched for nuclear launches for over 55 years, from Soviet intercontinental missiles to Iraqi Scuds.

Each satellite’s 6,000 infrared detectors sensed launches from geosynchronous orbit, and tracking shows both climbed hundreds of kilometres in September.

Space Based Infrared System satellites, flying since 2011, detect dimmer events and give longer warning.

The first Next-Generation Overhead Persistent Infrared satellite could launch on a Vulcan rocket within 12 months.

How each outlet framed it
Ars Technica
chronicles 55-year operational lifespan of 1970-launched Defense Support Program satellites, documents transition from Titan IIIC to SpaceX use of Cape SLC-40

Sources: Ars Technica