Defense Support Program

The Defense Support Program is the United States' original space-based missile warning system, in continuous service since 1970. DSP satellites carry large infrared telescopes in geostationary orbit to detect the hot plume of ballistic missile launches and nuclear detonations, providing the national command authority with tactical warning and attack assessment.

Twenty-three DSP satellites have been launched across successive blocks. The constellation is being retired as SBIRS completes its on-orbit build-out and Next-Gen OPIR comes online, though several DSP vehicles remain in operation as reserves. The program is a foundational element of the nuclear triad's command-and-control architecture.

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