A joint U.S./German space mission to track the continuous movement of water and other changes in Earth’s mass on and beneath the planet’s surface was successfully launched from the California coast on Tuesday.

The mission will measure changes in how mass is redistributed within and among Earth's atmosphere, oceans, land and ice sheets, as well as within Earth itself.

The twin spacecraft of the Gravity Recovery and Climate Experiment Follow-On (GRACE-FO), a joint NASA/German Research Centre for Geosciences (GFZ) mission, lifted off on a SpaceX Falcon 9 rocket from Space Launch Complex 4E at Vandenberg Air Force Base in California, sharing their ride into space with five Iridium NEXT communications satellites.

Ground stations have acquired signals from both GRACE-FO spacecraft. Initial telemetry shows the satellites are performing as expected. The GRACE-FO satellites are at an altitude of about 305 miles (490 kilometers), traveling about 16,800 mph (7.5 kilometers per second). They are in a near-polar orbit, circling Earth once every 90 minutes.

GRACE-FO will continue a study begun by the original GRACE mission, which proved that water movement can be tracked with high precision by its effect on Earth's gravitational field. GRACE-FO will continue the record of regional variations in gravity and about changes in glaciers, ground water, sea levels and the health of the planet as a whole.

“GRACE-FO will provide unique insights into how our complex planet operates,” said Thomas Zurbuchen, associate administrator of NASA’s Science Mission Directorate at NASA Headquarters. “Just as important, because the mission monitors many key aspects of the Earth’s water cycle, GRACE-FO data will be used throughout the world to improve people’s lives – from better predictions of drought impacts to higher quality information on use and management of water from underground aquifers.”

GRACE-FO continues the U.S./German partnership of the original GRACE mission, which operated from 2002 through 2017. “This mission continues and advances an amazing achievement of science and technology pioneered by the United States and Germany,” said Zurbuchen.

For 15 years, GRACE’s monthly maps of regional gravity variations provided new insights into how the Earth system functions and responds to change.

Among its innovations, GRACE was the first mission to measure the amount of ice being lost from the Greenland and Antarctic ice sheets. The mission improved understanding of the processes responsible for sea level rise and ocean circulation, provided insights into where global groundwater resources are shrinking or growing, showed where dry soils are contributing to drought, and monitored changes in the solid Earth, such as from earthquakes.

Frank Webb, GRACE-FO project scientist at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California, notes that to understand changes taking place in the climate system, scientists need data records several decades long.

"Extending the data record from GRACE will allow us to better distinguish short-term variability from longer-term trends," he said.