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DSAP-4A (Defense Satellite Application Program Block 4A) was the fourth version of the military meteorological satellites of the Defense Meteorological Satellite Program.

The DSAP-4A satellites, slightly larger than their predecessors, was 30 inches in diameter, 29 inches high, and weighed 175 pounds. Still spin-stabilized, the satellite nonetheless provided improved weather coverage.

Previously, the single 1/2-inch focal length RCA vidicon television camera in Block 1 and Block 2 satellites furnished a nadir resolution of 3-to-4 nautical miles (nm) over an 800 nm swath, with significant gaps in coverage of the Earth at the equator. Block 4 vehicles carried two one-inch focal length vidicons canted at 26 degrees from the vertical that provided global coverage of the Earth (contiguous coverage at the equator), along a 1,500 nm swath. The resolution varied from 0.8 nm at the nadir to 3 nm at the picture's edge. Besides a multi-sensor infrared subsystem, Block 4 also incorporated a high resolution radiometer that furnished cloud-height profiles. A tape recorder of increased capacity stored pictures of the entire northern hemisphere each day, while the satellite furnished real-time, direct local tactical weather coverage to small mobile ground or shipboard terminals.

The designation DMSP-4A (Defense Meteorological Satellite Program Block 4A) was retroactively assigned to these satellites.

Nation: USA
Type / Application: Meteorology
Operator: US Air Force (USAF), NRO
Contractors: RCA Astro
Equipment: ?
Propulsion: ?
Power: Solar cells, batteries
Orbit: SSO
Satellite COSPAR Date LS Launch Vehicle Remarks
DSAP-4A F1 (OPS 6026) 1966-082A 16.09.1966 Va 4300-B6 Thor-DSV2U Burner-2
DSAP-4A F2 (OPS 6073) 1967-010A 08.02.1967 Va 4300-B6 Thor-DSV2U Burner-2
DSAP-4A F3 (OPS 7202) 1967-080A 23.08.1967 Va LE-6 Thor-DSV2U Burner-2
DSAP-4A F4 (OPS 1264) 1967-096A 11.10.1967 Va LE-6 Thor-DSV2U Burner-2

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