New Moons Rising - GPS Declassified: From Smart Bombs to Smartphones - page 21

Fig. 1.3. Frank T. McClure ( cen-
ter ), director of the Research
Center at the Johns Hopkins Uni-
versity Applied Physics Labora-
tory, chats with physicists
William H. Guier ( left ) and
George C. Weiffenbach. (Cour-
tesy Johns Hopkins University
Applied Physics Laboratory)
Roger Easton, not wanting to uproot his young family, decided to remain
at the Naval Research Laboratory, where he turned his attention to one of
the few space projects retained by the laboratory—tracking spy satellites. 118
The challenge of building tiny transmitters to fit inside satellites and accu-
rate ground receivers to track them was replaced by the problem of tracking
silent satellites designed to evade detection. As head of the Space Surveil-
lance Branch, Easton led development of the Naval Space Surveillance Sys-
tem (sometimes shortened to navspasur, a moniker he never liked because
it confused the system with its command structure of the same name). 119 The
system still operates today as part of the larger Space Surveillance Network
directed by the U.S. Strategic Command in Omaha, Nebraska. 120 Space Sur-
veillance employs many of the same techniques used in Minitrack. A series
of six ground receivers spaced across the southern United States from San
Diego, California, to Fort Stewart, Georgia, forms a radar “fence,” but the
signals they track are generated not from satellites but by three large ground
transmitters in Alabama, Texas, and Arizona. As satellites pass over the fence,
continuous wave signals beamed into space by the transmitters bounce off
the satellites and are picked up by the ground stations. A central computer
at the program's headquarters in Dahlgren, Virginia, performs the high-
powered computing required for quickly calculating orbits. When the system
detected a large unknown satellite in late 1958, it created some excitement
at the Pentagon, but the object turned out to be Vanguard's third-stage booster
trailing behind the satellite. 121 The system's precision was sufficient to detect
even the strap that had secured the Vanguard satellite to the rocket. 122 With
improvements over the years, the system gained the capacity to detect
basketball-size objects in orbit out to a range of more than seventeen thou-