Global Positioning System Reference
In-Depth Information
Fig. 10.2. gps constellation, circa 2015. (Courtesy Lockheed Martin)
ability to operate more than thirty-two active satellites in the constellation.
The existing thirty-two satellite limit stems from the number of unique digital
identifiers, the prn codes (described in chapter 5), that were programmed into
the original system. There were thirty-seven prn sequences, with prns 1
through 32 assigned as sv id numbers and 33 through 37 reserved for other
uses. Those latter five prns are being redesignated for use by svs, and the new
control system will add twenty-six additional codes, prn numbers 38 through
63. 13 While nobody expects sixty-three gps satellites in orbit anytime soon,
the new technical specifications make that number possible.
The More the Merrier?
gps started with a constellation of twenty-one satellites and three spares. Over
time, users became accustomed to about thirty, and that threshold appears set
to grow. The Europeans adopted thirty as the size of the Galileo constellation
before the first launch. Russia, having restored glonass to twenty-four, wants
to expand to thirty. China is working toward a constellation of thirty to thirty-
 
 
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