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TIROS 9 / ESSA 1, ..., 9 (Operational TIROS)


The ESSA series was the second generation of US meterological satellites after the TIROS (Television & Infra-Red Observation Satellite) series. They were also called OT (Operational TIROS), TOS (TIROS Operational Satellite).

This desiign was a spin-stabilized operational meteorological spacecraft designed to take and record daytime cloudcover pictures on a global basis for subsequent playback to a ground acquisition station. The satellite had essentially the same configuration as that of the TIROS series, i.e., an 18-sided right prism, 107 cm across opposite corners and 56 cm high, with a reinforced baseplate carrying most of the subsystems and a cover assembly (hat). Electrical power was provided by approximately 10,000 1- by 2-cm solar cells that were mounted on the cover assembly and by 21 nickel-cadmium batteries.

Two redundant wide-angle cameras were mounted on opposite sides of the spacecraft and canted 75 deg from the spacecraft spin axis. A pair of crossed-dipole command and receiving antennas projected out and down from the baseplate. A monopole telemetry and tracking antenna extended up from the top of the cover assembly.

There were differences in the imaging system acorss the series:

  • TIROS 9 and ESSA 1 carried the same AVCS (Advanced Vidicon Camera System) as flown on previous TIROS mission, consisting of two 500 scan line TV cameras with 1.27 cm vidicons. At an altitude of 1450 km, the imaging system covered a 1200 km × 1200 km footprint with 3 km resolution.
  • Even-numbered ESSAs (2, 4, 6, 8) carried the APT (Automatic Picture Transmission) system with two redundant APT cameras with 2.54 cm diameter vidicons and 108 wide angle 1/1.8 objective lense with a focla lenghth of 5.7 mm. The imaging system was programmed to take four or eight APT pictures per orbit
  • Odd-numbered ESSAs (ESSA 3, 5, 7, 9) carried two AVCS (Advanced Vidicon Camera System) and the FPR (Flat Plane Radiometer) to measure the global distribution of reflected solar and long-wave radiation leaving the earth.

The satellites were placed in a cartwheel orbital mode, with its spin axis maintained normal to the orbital plane. The satellite spin rate and attitude were determined primarily by a Magnetic Attitude Spin Coil (MASC). The MASC was a current-carrying coil mounted in the cover assembly. The magnetic field induced by the current interacted with the earth's magnetic field to provide the necessary torque to maintain a desired spin rate of 9.225 rpm. Five small solid-fuel thrusters mounted around the baseplate provided a secondard means of controlling the spacecraft spin rate.

Nation: USA
Type / Application: Meteorology
Operator: ESSA
Contractors: RCA
Equipment: 2 × AVCS (#T9, 1, 3, 5, 7, 9); 2 × APT (#2, 4, 6, 8); FPR (#3, 5, 7, 9)
Propulsion: ?
Power: Solar cells, batteries
Mass: 138 kg (#T9, 1); 286 kg (#2, 4) 145 kg (#3, 5, 7, 9), 298 kg (#6, 8)
Orbit: SSO
Satellite COSPAR Date LS Launch Vehicle Remarks
TIROS 9 (A 54) 1965-004A 22.01.1965 CC LC-17A Delta-C
ESSA 1 (OT 3, TIROS 11) 1966-008A 03.02.1966 CC LC-17A Delta-C
ESSA 2 (OT 2, TIROS 12) 1966-016A 28.02.1966 CC LC-17B Delta-E
ESSA 3 (TOS 1, TIROS 13) 1966-087A 02.10.1966 Va SLC-2E Delta-E
ESSA 4 (TOS 2, TIROS 14) 1967-006A 26.01.1967 Va SLC-2E Delta-E
ESSA 5 (TOS 3, TIROS 15) 1967-036A 20.04.1967 Va SLC-2E Delta-E
ESSA 6 (TOS 4, TIROS 16) 1967-114A 10.11.1967 Va SLC-2E Delta-E1
ESSA 7 (TOS 5, TIROS 17) 1968-069A 16.08.1968 Va SLC-2E Delta-N
ESSA 8 (TOS 6, TIROS 18) 1968-114A 15.12.1968 Va SLC-2E Delta-N
ESSA 9 (TOS 7, TIROS 19) 1969-016A 26.02.1969 CC LC-17B Delta-E1
ESSA 10 (TOS H) - cancelled


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