GPS technology was in the news a lot during 2009.  It was number one on the British Science Association’s March 2009 list of “Top Ten Inventions that Changed the World,” and number seven on a travel-related list of “Top Ten Inventions that Changed the World of Tourism” six months later.  In October 2009, Google’s announcement about a free GPS navigation tool for smart phones sent shockwaves through the entire GPS navigation industry and caused stock prices to plummet for a number of existing GPS device manufacturers.   In November, GPS World reported that the Dutch government was initiating a distance-driven tax to replace the existing road tax on cars.  The new tax will be calculated by onboard GPS receivers and is intended to reduce carbon emissions and traffic congestion.  In December 2009, GPS was on the ABC News list of “The Top Ten Gadgets of the Decade,” second only to the iPod.

However, a report on GPS issued in May 2009 by the Government Accountability Office (GAO) was much less favorable.  The GAO concluded that if significant action was not taken by the Air Force to meet critical goals for modernizing the system, the older satellites in the GPS constellation will begin to fail in 2010, and it is likely that the total number of operational satellites will fall below the minimum number of 24 needed to provide the level of GPS service that the world has grown accustomed to.  Currently, about half of the existing GPS constellation is approaching “single thread” operation status, where a critical system error could render could render a satellite inoperative. 

It is possible this assessment is overly pessimistic, at least in the short term.  The constellation is currently at its maximum number of 30 active satellites and has another five deactivated spares as well as satellites that are “in the barn” on the ground, ready to launch on short notice.  However, the GPS III upgrade has been repeatedly delayed and further delays could endanger the integrity of the system.  Colonel Brad Parkinson, the original architect of the GPS, recently testified to substantial concerns regarding the risk of a GPS “brownout” that could arise from reduced satellite numbers. 

A reduction in operational satellites would cause performance degradations and a decline in positioning accuracy that would do more than simply reduce the accuracy of your car navigation systems or impact the ability of your GPS-enabled smart phone to find the nearest public transit station.  For example, many Enhanced-9-1-1 emergency calls, particularly from mobile carriers, rely on GPS technology to determine and transmit caller location data to emergency dispatch centers.  Power companies also use the precision timing of GPS to synchronize power plants and substations.  Without it, they will lose the vital ability to trace back failures in the power grid in the event of a major blackout, and restoration of power could be significantly hampered.  In addition, the airline industry may need to delay, cancel or reroute flights to allow for projected gaps in GPS coverage.  Military operations would be impacted as well. 

The United States controls the GPS constellation, and although civilian access has been allowed on a global scale since selective availability (SA) was discontinued in May 2000, there has been growing concern in other nations that some level of selective availability could be re-established in the event of another terrorist attack or hostile military actions against the United States.  While the GPS III system will not include any SA capabilities, these fears, along with a desire for independence and concerns about the aging satellite infrastructure, have spawned the development of alternate Global Navigation Satellite Systems (GNSS) that would compete with and/or complement the existing GPS constellation.  Unfortunately, these systems will not be operational in time to provide any back-up to the United States in the event of one or more satellite failures within the next couple of years.  

I’ll have more information about the alternate GNSS in my next blog post. 

A diagram of the existing GPS constellation showing 24 healthy satellites in orbit around the earth. Failure of any of these satellites could cause some level of performance degradation and a decline in positioning accuracy for GPS users worldwide. (Public domain image courtesy of http://pnt.gov/public/images/.)