At 10, GRACE Continues Defying, and Defining, Gravity
A decade after launch, NASA's GRACE space twins continue their orbital waltz, producing amazing science.
Just as  the lead characters in the popular Broadway musical "Wicked" sing about defying  gravity, the low-Earth orbiting twin spacecraft of NASA's Gravity Recovery and  Climate Experiment (GRACE) continue to defy gravity 10 years after launch,  while also continuing to help define it. Along the way, they've also produced an  amazing array of breakthrough science that is giving us a new understanding of  changes in Earth's natural systems.Launched  from Northern Russia on March 17, 2002, on what was designed to be a three- to  five-year mission, GRACE continues its task of making detailed measurements of  Earth's gravity field. It does so by noting minute changes in gravitational  pull caused by local changes in Earth's mass. Masses of ice, air, water and  solid Earth can be moved by weather patterns, seasonal change, climate change  and even tectonic events such as large earthquakes. To track these changes, GRACE  uses GPS and a microwave ranging system to measure micron-scale variations in  the 220-kilometer (137-mile) separation between the two spacecraft, developed  by NASA's Jet Propulsion Laboratory, Pasadena, Calif.These  measurements are used to produce monthly gravity maps that are more than 100  times more precise than previous models, providing the resolution necessary to  characterize how Earth's gravity field varies over time and space, and over  land and sea. The data have substantially improved the accuracy of techniques  used by oceanographers, hydrologists, glaciologists, geologists and climate  scientists."GRACE  essentially demonstrated a new form of remote sensing for climate research that  has turned out even better than we hoped," said GRACE Project Scientist Michael  Watkins of JPL "We realized early on in the design of GRACE that we could  measure the gravity field well enough to observe the critical indicators of  climate change - sea level rise and polar ice melt."GRACE  is a joint mission with the German Aerospace Center (DLR) and the German  Research Center for Geosciences (GFZ), in partnership with the University of  Texas at Austin. During its first decade of operations, the mission has  made remarkable contributions to many scientific disciplines, expanding our knowledge  of ice loss from the polar ice sheets and mountain glaciers, groundwater  storage on land, sea level variations and large-scale ocean circulation, to  name but a few.GRACE  also pioneered the study technique now being used by NASA's Gravity Recovery  and Interior Laboratory (GRAIL) mission, which recently began mapping the  gravitational field of the moon to learn about its internal structure and  composition in unprecedented detail. GRAIL data will also provide a better  understanding of how Earth and other rocky planets in the solar system formed  and evolved.In  June 2010, NASA and DLR signed an agreement to continue GRACE through 2015-a  full 10 years past the planned mission duration. Recognizing the importance of extending  this long-term dataset, NASA has approved the development and launch of the  GRACE Follow-On mission, also developed jointly with Germany, and planned for  launch in 2017.For  more information on GRACE, visit:http://www.csr.utexas.edu/grace/,http://www.nasa.gov/grace,  andhttp://grace.jpl.nasa.gov/. For more information on GRAIL, visit:http://www.nasa.gov/grail.