Chapter 10 — WATCH ROUTINES 



APOGEE — The point in orbit at which the satel- 

 lite is farthest from the center of the earth. 

 (See fig. 10-1 (D).) 



ARGUMENT OF SATELLITE — The geocentric 

 angle of a satellite measured in its orbital 

 plane from its ascending node in the direc- 

 tion the satellite is traveling. (Take a 

 basketball and place a mark on it at any 

 point. Start around the basketball to any 

 other point. Mark the two points, and meas- 

 ure the angle between lines drawn from these 

 two points to the center of the basketball. 

 This is the argument of satellite.) 



ASCENDING NODE — The point at the equator 

 at which the satellite in its orbital motion 

 crosses from the Southern to the Northern 

 Hemisphere, or the point at which the satel- 

 lite crosses the equator going from south 

 to north. This is the direction in which all 

 satellites move at the time of the ascending 

 node. (See fig. 10-1(E).) 



ASCENDING NODE TIME — The time when the 

 satellite passes the equator going from south 

 to north, or passes the ascending node. 



ATS— Applications Technology Satellite. 



DEGRADATION — The lessening of picture image 

 quality because of noise, rotation of the 



(A) 

 PERIGEE 



TERMINATOR 



TWILIGHT 

 ZONE 



(E) 



ASCENDING 



NODE 



EQUATOR 



IC) 



NODAL 

 INCREMENT 



D) 

 APOGEE 



209.276 

 Figure 10-1. — Diagrammatic drawing defining 

 orbital satellite technology. 



satellite, etc., or any optical, electronic, 

 or mechanical distortions in the image form- 

 ing system. 



DESCENDING NODE — The south bound equator 

 crossing of the satellite, or to put it another 

 way, the halfway point in one orbit. (The 

 descending node will be approximately 180 

 degrees of longitude from the ascending 

 node.) The earth moves from under the 

 satellite; if the earth did not move, the 

 descending node would be exactly 180 de- 

 grees from the ascending node. 



DISTORTION — An apparent warping and twist- 

 ing of a picture image received from a 

 satellite. This distortion has two causes — 

 electronic and optical. 



DMSP — Defense Meteorological Satellite Pro- 

 gram. 



EARTH-SYNCHRONOUS ORBIT — An orbit in 

 which the motion of the satellite is syn- 

 chronized with the motion of the earth so 

 that the satellite will appear stationary in 

 time and space. 



ESSA— Environmental Survey Satellite. 



GOES — Geostationary Operational Environmental 

 Satellite. 



HRPT — High Resolution Picture Transmission. 



INCLINATION— The angle between the plane 

 of the satellite orbit and the earth's equa- 

 torial plane. In other words, the angle at 

 which the satellite crosses the earth on its 

 ascending node, measured counterclockwise 

 from the equator. An angle of less than 

 90 degrees is called a prograde orbit, and 

 an angle of more than 90 degrees is called 

 a retrograde orbit. Inclination of a retro- 

 grade orbit is expressed by 180 degrees 

 minus the prograde inclination. Refer to 

 figure 10-1 (B) for an example of orbit in- 

 clination. 



IR — An infrared sensor that measures radiated 

 heat rather than reflected light. 



NESS— National Environmental Satellite Service. 



NO AA— National Oceanographic and Atmospheric 

 Administration. 



NODAL INCREMENT — Degrees of longitude be- 

 tween successive ascending nodes. (The earth 

 moves out from under the satellite during 

 the nodal period; the nodal increment is 

 the amount of turning measured in degrees 



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