Spenser Excerpt

Chaos and control over Washington, while the Pentagon burned.

(USAF / Staff Sgt. Greg L. Davis)
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But people weren’t done building on Espenscheid’s simple invention.  This collective activity would transform air travel and further enhance safety.


STARTING in the late 1970s, the United States began launching into orbit a constellation of satellites known collectively as the NAVSTAR Global Positioning System.  Maintained by the U.S. Air Force, this infrastructure is available to the entire world.  A minimum of 24 operational GPS satellites (actually just over 30 at the time of this writing) girdle the earth in highly inclined orbits that ensure excellent coverage of the entire world.

GPS is freely available to aircraft, ground vehicles, ships, soldiers, scientists, hikers, and any other users worldwide.  This system provides accurate positioning to within one meter (about a yard) for civil users.  With atomic clocks aboard all the satellites, GPS also provides astonishingly accurate time information.

Other satellite navigation systems are also today being fielded or planned, notably Russia’s GLONASS and the European Union’s Galileo systems.  In addition to those global constellations, China and India have regional systems in the works.  For simplicity’s sake, therefore, the pioneering GPS system and those that follow are today collectively referred to as the global navigation satellite system (GNSS).

Aviation relies heavily on this GNSS infrastructure.  Jetliners flying the world’s oceans can be certain of their position despite the lack of positive radar coverage at sea.  And where GNSS is augmented regionally by one or more ground-based transmitters, it becomes even more accurate, allowing civil aircraft to fly precise instrument landing approaches without the need for traditional instrument landing systems located at the airport itself.


From The Airplane: How Ideas Gave Us Wings by Jay Spenser. Courtesy of HarperCollins Publishers.


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