* Astronomy

NASA Pinning Down Where 'Here' is Better Than Ever

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 Centre 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 demonstration station and merger of technique processing, known as the Space Geodesy Project, will serve as an example of what is required to measure Earth's properties to keep up with the ever-changing, yet subtle, movements in land as it rises and sinks along with shifts in the balances of the atmosphere and ocean. All of these movements tweak Earth's shape, its orientation in space and its center of mass -- the point deep inside the planet that everything rotates around. The changes show up in Earth's gravity field and literally slow down or speed up the planet's rotation.
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