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ESSA 4 was a sun-synchronous operational meteorological satellite designed to provide real-time earth cloudcover TV pictures to properly equipped ground receiving stations for use in weather analysis and forecasting. The satellite had essentially the same configuration as that of the TIROS spacecraft, 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 Automatic Picture Transmission (APT) cameras were mounted on opposite sides of the spacecraft with their optical axes perpendicular to the spin axis. Projecting downward from the baseplate were a pair of crossed-dipole command reception antennas. A monopole telemetry (136.500 MHz) and tracking (136.770 MHz) antenna extended outward from the top of the cover assembly. The satellite spin rate was controlled by means of a Magnetic Attitude Spin Coil (MASC), with the spin axis maintained normal to the orbtial plane (cartwheel orbit mode) to within plus or minus 1 deg. 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 torque necessary to maintain a desired spin rate of 10.9 rpm. With the exception of the failure of one of the APT cameras, the spacecraft performed normally after launch. It was turned operationally off on December 6, 1967, and was finally deactivated on May 5, 1968.

Alternate Names

  • 02657
  • ESSA4
  • TOS-B

Facts in Brief

Launch Date: 1967-01-26
Launch Vehicle: Delta
Launch Site: Vandenberg AFB, United States
Mass: 285 kg

Funding Agency

  • Environmental Science Service Administration (United States)


  • Earth Science

Additional Information

Questions and comments about this spacecraft can be directed to: Coordinated Request and User Support Office



NameRoleOriginal AffiliationE-mail
Mr. William H. JonesProject ManagerNASA Goddard Space Flight
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