(that is, whether the spacecraft could fly from the South Pole toward the 

 North Pole on the daylight side of its orbit). The study showed: that the 

 spacecraft can, indeed, operate successfully in such an orbit; that the 

 CZCS, less the radiation cooler, can fit on the spacecraft; and that the 

 present data system could be enlarged to accommodate data transmission 

 from the CZCS to the ground. 



The parameters of an orbit under consideration for the series of Advanced 

 Tiros-N (ATN) satellites that could carry a CZCS are summarized in Table 5- 

 2. The inclination of the orbit is necessary in order to preserve the sun 

 synchronous characteristic so that the orbit plane may precess at the same 

 rate as the earth rotates around the sun. NASA/GSFC also addressed the 

 question of whether the necessary space was available on the earth-viewing 

 portion of the ATN in order to accommodate a future CZCS (see Appendix A) 

 and the necessary data processing system to support it. Figure 5-1 shows 

 the bottom, or earth-viewing side, of the ATN and a location which can 

 accommodate the CZCS and the color data processor needed to support the 

 instrument. Unfortunately, the end of the spacecraft where radiation 

 coolers may be utilized is fully occupied by the AVHRR, the SSU, and the 

 HIRS; therefore, the CZCS will have to fly without a radiation cooler, 

 eliminating the 10.5 to 12.5 micrometer band. This is not a serious 

 problem in that the AVHRR, which operates continually, provides thermal 

 measurements in the split window of 10.5 to 11.5, and 11.5 to 12.5 micro- 

 meters over the ocean. There will be some problems registering the thermal 

 data with the color data since the AVHRR will not have the tilt mechanism 

 of the CZCS and the mirrors are not synchronized. Nevertheless, the CZCS 

 fits fairly comfortably into the bottom of the ATN. 



Table 5-2. NOAA-I/CZCS Orbit Parameters 



Parameter Nominal Value 



Altitude (km) 870 

 Inclination (degrees) 98.899 

 Nodal period (minutes) 102.368 

 Nodal regression (degrees/revolution) 25.592 

 Nodal precession (degrees/day) 0.9856 

 Orbits per day 14.067 

 Sun angle range limits (degrees) 46-80 



5-3 



