Pictures, taken once every 26O seconds, are usually obtained in 



sequences of twelve frames to a pass. During development at NESC , each 

 frame is electronically gridded by computer with latitude and longitude 

 lines and geographic outlines are merged with the picture. An identification 

 legend beneath each picture provides pertinent information. 



ESSA 3 was launched on 2 October I966 by the National Aeronautics 

 and Space Administration and was put into a nearly circular, sun-synchronous, 

 polar orbit, approximately 1,^35 km. {'^'jh nm. ) above the earth's surface 

 with an apogee of 1,U86 km. (802 nm. ) and a perigee of 1,382 km. {^h6 nm. ) . 

 The orbit inclined 101.0° to the equatorial plane with a nodal period of 

 IIU.5 minutes which corresponds to slightly more than I3 revolutions of 

 the earth each day. 



Because of a drift problem with respect to its sun-synchronous 

 position ESSA 3 was put into standby mode on 9 October I968. It is now 

 considered completely inoperative with no chance of operational recovery. 



ESSA ^ was launched on 20 April I967. Like ESSA 3, it was put into a 

 nearly circular polar orbit, approximately 1,386 km. {"jhQ nm. ) above 

 the earth's surface, with an apogee of 1,423 km. (768 nm. ) and a perigee 

 of 1,351 km. (729 nm.). The orbit inclines 101.9° to the equatorial 

 plane with an orbital period of II3.6 minutes which corresponds to 12.7 

 passes around the earth each day. 



ESSA 7 , the most recent AVCS satellite in the TOS series, was launched 

 on 16 August 1968. It, too, was placed into a nearly circular, sun- 

 synchronous, polar orbit approximately 1,^52 km. {iQh nm. ) above the 

 earth with an apogee of 1,^73 (795 nm, ) and a perigee of 1,^1-30 km. 

 (772 nm. ), The orbit is inclined 101.7° to the equatorial plane. 



58 



