NASA pinning down 'here' better than ever

Elizabeth Zubritsky in Space Daily via NASA's Goddard Space Flight Center: 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 initiative is run by Goddard Space Flight Center in Greenbelt, Md., where the next generation of two of these systems is being developed and built. And Goddard, in partnership with NASA's Jet Propulsion Laboratory in Pasadena, Calif., is bringing all four systems together in a state-of-the-art ground station.

"NASA and its sister agencies around the world are making major investments in new stations or upgrading existing stations to provide a network that will benefit the global community for years to come," says John LaBrecque, Earth Surface and Interior Program Officer at NASA Headquarters.

GPS won't be the only beneficiary of the improvements. All observations of Earth from space-whether it's to measure how far earthquakes shift the land, map the world's ice sheets, watch the global mean sea level creep up or monitor the devastating reach of droughts and floods-depend the International Terrestrial Reference Frame, which is determined by data from this network of designated sites.

Earth is a shapeshifter. Land rises and sinks. The continents move. The balance of the atmosphere shifts over time, and so does the balance of the oceans. All of this tweaks Earth's shape, orientation in space and 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....

Navstar-2F satellite of the Global Positioning System (GPS), from NASA