Success Has Many Fathers - GPS Declassified: From Smart Bombs to Smartphones - page 48

planes, with eight-hour orbits would be optimal. Ground stations were to be
placed in Alaska, St. Croix in the Virgin Islands, Guam, and Samoa. 27 Security
concerns limited ground locations to either the United States or U.S. territo-
ries. This restriction was eliminated in the 1990s after the end of the Cold War
with the placement of stations in less secure areas, such as Diego Garcia in the
central Indian Ocean. Eight-hour orbits were preferred to twelve-hour orbits
since they provided more frequent clock updates and minimized the problems
from not having a station in the Indian Ocean. Twelve-hour orbits became
more feasible when atomic clocks replaced quartz crystal oscillators in the sat-
ellites, reducing the need for ground updates.
A widespread myth is that worldwide time synchronization was an unex-
pected consequence of gps. “Certainly there was no serious consideration
given to gps becoming the de facto world standard for time,” blogged Don
Jewell in January 2008. 28 Jewell spent more than thirty years in the Air Force
and writes for gps Wo rld . A 2009 dissertation posited that, “somewhat unex-
pectedly, the precise timing information transmitted by gps satellites was
quickly incorporated into many inventive applications that are not related to
navigation.” 29 On the contrary, both Roy Anderson and Roger Easton antici-
pated worldwide clock synchronization. Anderson wrote in 1964 that his sys-
tem would provide worldwide synchronization to approximately one
microsecond. 30 Easton wrote in 1967 that “possible fallouts from such a sys-
tem are worldwide time synchronized to better than 0.1 microsecond.” 31 Thus
the timing was more accurate by a factor of ten. In the Timation Development
Plan , published in 1971, the estimated time transfer accuracy was improved
again by a factor of ten, to better than 0.01 microsecond. Easton stated in 1974
that “precise orbiting clocks will prove to be a valuable tool in a variety of appli-
cations, by providing the entire planet earth with a single, accurate time sys-
tem, enveloping the globe in a web of synchronized satellite signals.” 32 This
was about fifteen years before the term World Wide Web was coined. These
satellite navigation proposals provided three-dimensional position and time.
Even though time was less prominent than positioning, it was extremely impor-
tant. Today, space-based navigation systems are often referred to as providing
pnt, which means positioning, navigation, and timing. Time-transfer experi-
ments via satellite began with the Timation I satellite in early 1968. Timation
II performed the first international time transfer in July 1972 between the Royal
Greenwich Observatory, England, and the Department of Defense Master
Clock at the U.S. Naval Observatory in Washington dc. 33