Before our Global Positioning System (GPS) navigation devices can tell us where we are, the satellites that make up the GPS need to know exactly where they are. For that, they rely on a network of sites that serve as "you are here" signs planted throughout the world. The catch is, the sites don't sit still because they're on a planet that isn't at rest, yet modern measurements require more and more accuracy in pinpointing where "here" is. To meet this need, NASA is helping to lead an international effort to upgrade the four systems that supply this crucial location information. NASA's Jet Propulsion Laboratory, Pasadena, Calif., in partnership with NASA's Goddard Space Flight Center in Greenbelt, Md., where the next generation of laser ranging and radio interferometry systems is being developed and built, is bringing all four systems together in a state-of-the-art ground station.
This is interesting. Details here.
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