AEROGRAPHER'S MATE 3 & 2 



of longitude, that takes place during one 

 nodal period.) (See fig. 10-1.) 



NODAL PERIOD— The time elapsing between 

 successive passages of the satellite through 

 the ascending nodes. 



ORBIT — One complete circling of the earth toy 

 a satellite from a reference point to the 

 same reference point. 



ORBIT NUMBER — Refers to a particular cir- 

 cuit beginning at the satellite's ascending 

 node. The number from launch to the first 

 ascending node is designated as ZERO. 



PERIGEE — The point in orbit at which the sat- 

 ellite is closest to the center of the earth. 

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



POLAR ORBIT — An orbit in which the satellite 

 would pass over both of the earth's poles. 



PRINCIPAL POINT — The point on earth where 

 the camera is focused at any time during 

 the orbit. If the camera's vertical axis is 

 perpendicular to the earth's surface, the 

 principal point coincides with the subpoint. 

 (See fig. 10-2(A).) 



SMS — Synchronous Meteorological Satellite. 



SR — Scanning Radiometer. 



SUBPOINT — The point on earth directly below 

 the satellite at any given time during its 

 orbit. (See fig. 10-2(B).) 



SUBPOINT TRACK — Projection of satellite or- 

 bit on a rotating earth. It is the satellite's 

 projected path over the earth's surface with 

 a moving earth. From information obtained 

 from the subpoint track, the antenna can be 

 pointed in the direction of the satellite. (See 

 fig. 10-2(C).) 



SUN TIME — The time of the day according to 

 the sun. It has nothing to do with local 

 time or Zulu time. 1200 sun time is the 

 time that the sun is directly overhead. 1300 

 sun time is the time when the sun is ex- 

 actly 15 degrees of longitude to the west 

 of the longitude where it was at 1200. 



SUN-SYNCHRONOUS ORBIT — An orbit in which 

 the satellite will always pass over the equa- 

 tor at the same sun time on each of its 

 orbits. 



TERMINATOR — A line on the globe separating 

 the daylight side of the globe from the night- 

 time side. (See fig. 10-1 (F).) 



TIME PAST ASCENDING NODE — The amount of 

 time for a body in orbit to advance from the 

 last ascending node to an arbitrary position. 



TRACKING— Procedures for keeping the an- 

 tenna pointed at the satellite as it moves 

 through its orbit. 



TRACKING OR PLOTTING BOARD — Polar pro- 

 jection diagram of the earth centered at 

 either pole and extending to 30 degrees of 

 latitude past the equator into the other hemi- 

 sphere. The board has radials from the pole 

 representing 1-degree intervals of longitude; 

 each fifth radial is accentuated. Concentric 

 circles on the projection represent latitudes. 



TRACKING DIAGRAM — The tracking diagram 

 was constructed to show azimuth and dis- 

 tance of the satellite from the station for 

 a given subpoint position. 



A different tracking diagram is provided 

 for each 5-degree latitude belt. The diagram 

 drawn for the latitude closest to that of the 

 ground station should be used. 



CAMERA 



NADIR ANGLE 



(A) 

 PRINCIPAL 

 POINT 



209.277 

 Figure 10-2. — Diagrammatic drawing defining 

 satellite tracking terminology. 



178 



