DSP-20 (USA-149)

The DSP Block-3 (or DSP-I) satellites represent the third generation of DSP early warning satellites, each costing approximately $180 million. These spacecraft utilize slow spinning (6 rpm) around the nadir axis to enable Earth scanning by the detector system, while zero momentum (three-axis) stabilization is achieved using a reaction wheel to counter the spacecraft spin. With four deployed solar panels, they generate roughly 1300 W of power. DSP satellites are radiation hardened and feature a classified payload, likely consisting of a telescope with a 6000-element IR array, nuclear explosion detectors, and particle detection monitors.