Issue link: https://read.dmtmag.com/i/62129
GPS coordinates during his famous ride? Our 21st century soldiers routinely use this technology in their activities, but it's fascinating to imagine how world history may have been altered with precise navigation tools. In addition to military applications, GPS has evolved into the world navigation standard for civil avia- tion, accurate survey, financial transactions, precision agriculture and vehicle navigation. W Across the globe, humanity freely uses GPS naviga- tion signals after purchasing receivers with preloaded software packages. A simple map and calming voice emanate from automobile dashboards, but the true source is a constellation of up to 32 GPS satellites orbiting Earth 12,500 miles overhead. Applying trilateration—similar to triangulation, but based on timing—GPS receivers use each satellite signal's "time of arrival" to sequentially solve for its location derived from the satellite's location in space. By determining the distance from the receiver to each satellite for at least four satellites, the receiver deter- mines its unique location. The Next Generation With GPS at the world's core navigation infrastructure, it's good to know the United States will continue to sustain and modernize "the" Global Positioning System. Entering service in 2014 will be the modern- ized GPS III satellites, which are the "next generation" of advanced navigation satellites. Each GPS III satellite will deliver up to four-times bet- ter accuracy due, in part, to improved atomic clocks. In fact, the GPS III atomic clocks are so accurate they lose only about one second every 1.5 million years (more than 50 trillion seconds). Interestingly, every nanosec- ond (billionth of a second) error in a GPS atomic clock contributes about one foot of location error. This is exciting technology given that these clocks now syn- chronize computer networks worldwide. After a U.S. GPS satellite has been launched into space, military operators closely monitor each satellite's performance and ensure the entire GPS Mobility/GPS Special Issue hat if the "one if by land, two if by sea" lan- terns at Boston's Old North Church could've been replaced with Paul Revere shouting constellation maintains close time synchronization. GPS is operated by the outstanding men and women of Air Force Space Command's 2nd Space Operations Squadron, based at Schriever Air Force Base, Colo. They manage and operate the GPS constellation and keep each satellite at top performance, so GPS receiv- ers worldwide receive the best navigation signals. These dedicated operators are making preparations to support the new GPS III satellites. Increased Accuracy, Power and Longevity GPS III satellites will broadcast a new civil signal (L1C) interoperable with other international satellite sys- tems such as Japan's Quasi-Zenith Satellite System and Europe's Galileo system. When broadcast by Lockheed Martin's GPS III satellite features a new robust civil navigation signal and increased power military signals. Operating at an altitude of 20,200 kilometers, GPS III has an average revisit time of 12 hours and will have an on-orbit service life of 15 years (10,950 revolutions around Earth). APRIL 2O12 / WWW . GEOPLA CE . COM 15