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Tophat 1, 2 (P-11 4423, 4428)

Tophat 1 [NSA]

The Tophat (sometimes also refered to by Top Hat) satellites were 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 Tophat communications intelligence (COMINT) payloads were used to intercept troposcatter communications signals in the 450–1000 MHz range, analyze the transmitted signal characteristics, and sample the signal information content. Tophat was equipped with four identical antennas in two arrays—two pointing up and two pointing down. It was equipped with three tape recorders, one serving as backup. It was not capable of operating in transpond mode, meaning that data had to be recorded and dumped. The satellite could provide geopositioning data to an accuracy of approximately 18 to 46 km.

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 or later on a rack on the KH-9 Hexagon reconnaissance satellite. 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.

These subsatellites were deployed from the propulsion rack of the Agena-D stage of a KH-4B Corona or directly from a KH-9 Hexagon reconnaissance satellites. They used two solid-fuel kick-motors to maneuver themselves into their operational orbits after deployment.

Nation: USA
Type / Application: SIGINT, COMINT
Operator: US Air Force (USAF)
Contractors: Lockheed (bus); Ling Tempco Vought → E-Systems (payload)
Equipment: ?
Configuration: P-11 bus
Propulsion: Kick motor
Power: Solar cells, batteries
Lifetime: 9 months (planned); 44 month reached (#1)
Mass: 171 kg (#2)
Orbit: 478 km × 508 km, 83.19° (#1); 501 km × 528 km, 94.00° (#2)
Satellite COSPAR Date LS Launch Vehicle Remarks
Tophat 1 (P-11 4423, Mission 7334, OPS 6829) 1970-098B 18.11.1970 Va SLC-3W Thorad-SLV2H Agena-D with KH-4B 12
Tophat 2 (P-11 4428, Mission 7340, OPS 4547) 1974-020C 10.04.1974 Va SLC-4E Titan-3D with KH-9 8, IRCB

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