The Fanion Slewto satellite was part of a series of so called Program 11 or P-11 "Subsatellite Ferrets", low orbit ELINT/SIGINT satellites to pinpoint and characterize different Radar emitters in the Soviet Union and Warsaw pact states.
The satellites were based on Lockheed's P-11 bus, which was designed to fit on the aft rack of the Agena-D upper stage. The bus contained each one or two focused payload black boxes and different antenna configurations according to payload, as well as deployable solar arrays. The satellite featured two solid rocket motors, which allowed them to rise and circularize their orbit after deployment from the host satellite. Both spin or gravity gradient stabilization was possible.
Fanion was a SIGINT mission targeted at EOB and Slewto was targeted at Hen House radars. Fanion derived a pencil beam from a Milss-Cross antenna pattern using two receivers and compared outputs. An accurate pointing angle measurements resulted when the satellite spun the crossing fan beams directly at the emitter.
This subsatellite was deployed from the propulsion rack of the Agena-D stage of a KH-4A Corona reconnaissance satellite. It used two solid-fuel kick-motors to maneuver itself into its operational orbit after deployment.
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