(3) Correction to universal time as 2 time code characters; 

 sign of correction (1111 = +, 0000 = -), and tenths of 

 seconds corrected. 



(4) Satellite ephemeris in geocentric measure as thirteen 4- 

 bit time code characters; longitude in degrees (hundreds), 

 (tens), (units), (1/10's), (1/100's); latitude in degrees 

 (sign), (units), (1/10's), (1/100's), orbital radius 

 correction in microseconds (sign), (hundreds), (tens), 

 (units) . 



NBS Technical Note 681, "A Satellite-Controlled Digital Clock," 

 describes use of the time code data transmitted via the DCS 

 Interrogate signal to obtain continuously updated time-of-year 

 data at a sensor platform site to an accuracy of about 100 micro- 

 seconds with +20-microsecond precision. 



2.2.4 Platform Radio Set Characteristics 



A sensor platform does not need to be equipped to receive the 

 Command/Interrogate signal for operation in the DCS. The additional 

 flexibility provided by the Command/Interrogate capability may be 

 desirable, for example, when the data reporting schedule requires 

 modification or when the sensor activities must be directed 

 remotely. 



The requirements for a sensor platform radio set are described in 

 NOAA/NESS Specification No. 200.004, "Data Collection Platform Radio 

 Set Specification." The design characteristics of platform radio 

 sets essential to operation in the DCS are presented in Appendix C, 

 "Platform Radio Set Certification Requirements." 



2.2.5 Environmental Considerations 



Efficient utilization of the DCS capability for timely data 

 collection from unattended sensor sites requires that platform radio 

 sets be able to operate within specifications for all environmental 

 conditions to which they are exposed. Environmentally induced 

 performance changes may result in loss of important data from the 

 affected sensor platform, as well as from other platforms which 

 experience interference produced by the malfunctioning equipment. 



2.3 Spacecraft Function in the DCS 



2.3.1 Communication Transponder 



The spacecraft (GOES) operates as a cross-strapped transponder 

 within the DCS communications chain. Command/Interrogate signals 

 from the CDA station are received by the spacecraft at S-band, then 

 translated to UHF and retransmitted through an Earth-coverage antenna 

 to the field of deployed sensor platforms. Response signals from 

 the sensor platform sites are received by the spacecraft at UHF, 

 translated to S-band, and sent to the CDA Station. The spacecraft 

 transponder Is fully redundant to guard against DCS outages, because 

 of premature equipment failure. 



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