The DSP (Defense Support Program) Block-3 (a.k.a DSP-I)
satellites are the third generation of DSP early warning satellites, which cost about $
180M per spacecraft.
The Spacecraft spins slowly (6 rpm) about the nadir axis to permit scanning of the
Earth by the detector system. Zero momentum (three axis) stabilized using a reaction wheel
to counter the spacecraft spin. Four solar panels deploy to generate roughly 1300 W. The
DSP are radiation hardened. The payload is classified, but is probably a telescope with
6000 element IR array, nuclear explosion detectors, particle detection monitors.
DSP 23 failed less then a year after launch and was inspected by the MITEx A and MITEx B satellites in orbit.
DSP 16 was retired in 2016 and was moved into a graveyard orbit above the geostationary belt.
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