GPS chaos: How a $30 box can jam your life
IT WAS just after midday in San Diego, California, when the disruption started. In the tower at the airport, air-traffic controllers peered at their monitors only to find that their system for tracking incoming planes was malfunctioning. At the Naval Medical Center, emergency pagers used for summoning doctors stopped working. Chaos threatened in the busy harbour, too, after the traffic-management system used for guiding boats failed. On the streets, people reaching for their cellphones found they had no signal and bank customers trying to withdraw cash from local ATMs were refused. Problems persisted for another 2 hours.
It took three days to find an explanation for this mysterious event in January 2007. Two navy ships in the San Diego harbour had been conducting a training exercise. To test procedures when communications were lost, technicians jammed radio signals. Unwittingly, they also blocked radio signals from GPS satellites across a swathe of the city.
Why would a GPS outage cause such disruption? These satellite signals now do a lot more than inform your car's satnav. GPS has become an "invisible utility" that we rely on without realising. Cellphone companies use GPS time signals to coordinate how your phone talks to their towers. Energy suppliers turn to GPS for synchronising electricity grids when connecting them together. And banks and stock exchanges use the satellites for time-stamps that prevent fraud. Meanwhile, our societies' reliance on GPS navigation is growing by the year.
