The Environmental Survey Satellite (ESSA) 



The ESSA series includes operational satellites providing routine, daily 

 global coverage of the entire earth from space. 



With the launching of ESSA 2, the TIROS Operational System (TOS) 

 series was started (ESSA 1 was sponsored by the U.S. Department of 

 Commerce). ESSA 2 was part of a pair of satellites which makes up the 

 TOS twins: one Automatic Picture Transmission System (APT) satellite 

 (even numbered ESSA) and one Advance Vidicon Camera System (AVCS) satellite 

 (odd numbered ESSA). The APT satellites do not store video data but transmit 

 data immediately for worldwide direct readout. The AVCS satellites 

 store their global video data for readout at one of the Command and Data 

 Acquisition (CDA) stations at Fairbanks, Alaska or Chincoteague, Virginia 

 where the data is transmitted to ESSA's National Environmental Satellite 

 Center (NESC) at Suitland, Maryland. 



The odd numbered satellites are of greater interest oceanographically 

 because their data are referenced and catalogued and therefore retrievable 

 for historic study. The following, discussion, therefore, deals with 

 ESSA 3, 5, and 7. 



The ESSA satellite is positioned in a "cartwheel" configuration in 

 space to allow earth-oriented picture coverage. The spin axis of the 

 satellite is normal to the plane of the orbit and the rim-mounted cameras 

 view the earth once during each revolution about the spacecraft axis. 



The cameras in the satellite are one-inch diameter vidicons of the 

 AVCS type. Although one camera provides full global coverage, two 

 cameras are operated to give full system redundancy. Each of the cameras 

 independently takes pictures and stores them for later playback to one 

 of the CDA stations. The CDA stations are able to get data from the 

 satellite during thirteen of the fourteen daily orbital passes. 



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