This artist's rendering shows the twin spacecraft of the Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) mission, a partnership between NASA and the German Research Centre for Geosciences (GFZ). GRACE-FO is a successor to the original GRACE mission, which began orbiting Earth on March 17, 2002. GRACE-FO will carry on the extremely successful work of its predecessor while testing a new technology designed to dramatically improve the already remarkable precision of its measurement system. The GRACE missions measure variations in gravity over Earth's surface, producing a new map of the gravity field every 30 days. Thus, GRACE shows how the planet's gravity differs not only from one location to another, but also from one period of time to another. https://photojournal.jpl.nasa.gov/catalog/PIA21607

Artist's rendering of the twin spacecraft of the Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) mission, scheduled to launch in May, 2018. GRACE-FO will track the evolution of Earth's water cycle by monitoring changes in the distribution of mass on Earth. https://photojournal.jpl.nasa.gov/catalog/PIA22431

The Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) twin satellites, attached to turntable fixtures, at the Astrotech Space Operations processing facility at Vandenberg Air Force Base, California. GRACE-FO will extend GRACE's legacy of scientific achievements, which range from tracking mass changes of Earth's polar ice sheets and estimating global groundwater changes, to measuring the mass changes of large earthquakes and inferring changes in deep ocean currents, a driving force in climate. To date, GRACE observations have been used in more than 4,300 research publications. Its measurements provide a unique view of the Earth system and have far-reaching benefits to society, such as providing insights into where global groundwater resources may be shrinking or growing and where dry soils are contributing to drought. GRACE-FO is planned to fly at least five years. https://photojournal.jpl.nasa.gov/catalog/PIA22338

The Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) twin satellites, attached to turntable fixtures, at the Astrotech Space Operations processing facility at Vandenberg Air Force Base, California. GRACE-FO will extend GRACE's legacy of scientific achievements, which range from tracking mass changes of Earth's polar ice sheets and estimating global groundwater changes, to measuring the mass changes of large earthquakes and inferring changes in deep ocean currents, a driving force in climate. To date, GRACE observations have been used in more than 4,300 research publications. Its measurements provide a unique view of the Earth system and have far-reaching benefits to society, such as providing insights into where global groundwater resources may be shrinking or growing and where dry soils are contributing to drought. GRACE-FO is planned to fly at least five years. https://photojournal.jpl.nasa.gov/catalog/PIA22340

One of the two Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) satellites and its turntable fixture at the Astrotech Space Operations processing facility at Vandenberg Air Force Base, California. GRACE-FO will extend GRACE's legacy of scientific achievements, which range from tracking mass changes of Earth's polar ice sheets and estimating global groundwater changes, to measuring the mass changes of large earthquakes and inferring changes in deep ocean currents, a driving force in climate. To date, GRACE observations have been used in more than 4,300 research publications. Its measurements provide a unique view of the Earth system and have far-reaching benefits to society, such as providing insights into where global groundwater resources may be shrinking or growing and where dry soils are contributing to drought. GRACE-FO is planned to fly at least five years. https://photojournal.jpl.nasa.gov/catalog/PIA22339

The Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) twin satellites, attached to turntable fixtures, at the Astrotech Space Operations processing facility at Vandenberg Air Force Base, California. GRACE-FO will extend GRACE's legacy of scientific achievements, which range from tracking mass changes of Earth's polar ice sheets and estimating global groundwater changes, to measuring the mass changes of large earthquakes and inferring changes in deep ocean currents, a driving force in climate. To date, GRACE observations have been used in more than 4,300 research publications. Its measurements provide a unique view of the Earth system and have far-reaching benefits to society, such as providing insights into where global groundwater resources may be shrinking or growing and where dry soils are contributing to drought. GRACE-FO is planned to fly at least five years. https://photojournal.jpl.nasa.gov/catalog/PIA22341

The Gravity Recovery and Climate Experiment Follow-on (GRACE-FO) mission is a partnership between NASA and the German Research Centre for Geosciences (GFZ). GRACE-FO is a successor to the original GRACE mission, which began orbiting Earth on March 17, 2002. GRACE-FO will carry on the extremely successful work of its predecessor while testing a new technology designed to dramatically improve the already remarkable precision of its measurement system. The GRACE missions measure variations in gravity over Earth's surface, producing a new map of the gravity field every 30 days. Thus, GRACE shows how the planet's gravity differs not only from one location to another, but also from one period of time to another. Airbus Defence and Space (Friedrichshafen/Germany) is the industrial prime contractor to build the satellites.

Karen Fox, of NASA's Office of Communications, introduces Michael Watkins, GRACE-FO science lead and director of NASA's Jet Propulsion Laboratory and Frank Webb, GRACE-FO project scientist at JPL, during a briefing on the upcoming launch of the Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) mission, Monday, April 30, 2018 at NASA Headquarters in Washington. The twin GRACE-FO spacecraft will measure and monitor monthly changes in how mass is redistributed within and among Earth's atmosphere, oceans, land and ice sheets, as well as within Earth itself. Photo Credit: (NASA/Joel Kowsky)

Karen Fox of NASA's Office of Communications, introduces David Jarrett, GRACE-FO program executive in the Earth Science Division at NASA Headquarters and Phil Morton, NASA GRACE-FO project manager at JPL, during a briefing on the upcoming launch of the Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) mission, Monday, April 30, 2018 at NASA Headquarters in Washington. The twin GRACE-FO spacecraft will measure and monitor monthly changes in how mass is redistributed within and among Earth's atmosphere, oceans, land and ice sheets, as well as within Earth itself. Photo Credit: (NASA/Joel Kowsky)

Frank Webb, GRACE-FO project scientist at JPL, discusses the upcoming launch of the Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) mission, Monday, April 30, 2018 at NASA Headquarters in Washington. The twin GRACE-FO spacecraft will measure and monitor monthly changes in how mass is redistributed within and among Earth's atmosphere, oceans, land and ice sheets, as well as within Earth itself. Photo Credit: (NASA/Joel Kowsky)

Frank Flechtner, GRACE-FO project manager for the German Research Centre for Geosciences (GFZ) in Potsdam, Germany, participates in a briefing on the upcoming launch of the Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) mission via a remote video link, Monday, April 30, 2018 at NASA Headquarters in Washington. The twin GRACE-FO spacecraft will measure and monitor monthly changes in how mass is redistributed within and among Earth's atmosphere, oceans, land and ice sheets, as well as within Earth itself. Photo Credit: (NASA/Joel Kowsky)

Frank Webb, GRACE-FO project scientist at JPL, discusses the upcoming launch of the Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) mission, Monday, April 30, 2018 at NASA Headquarters in Washington. The twin GRACE-FO spacecraft will measure and monitor monthly changes in how mass is redistributed within and among Earth's atmosphere, oceans, land and ice sheets, as well as within Earth itself. Photo Credit: (NASA/Joel Kowsky)

Michael Watkins, GRACE-FO science lead and director of NASA's Jet Propulsion Laboratory, discusses the upcoming launch of the Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) mission, Monday, April 30, 2018 at NASA Headquarters in Washington. The twin GRACE-FO spacecraft will measure and monitor monthly changes in how mass is redistributed within and among Earth's atmosphere, oceans, land and ice sheets, as well as within Earth itself. Photo Credit: (NASA/Joel Kowsky)

David Jarrett, GRACE-FO program executive in the Earth Science Division at NASA Headquarters, discusses the upcoming launch of the Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) mission, Monday, April 30, 2018 at NASA Headquarters in Washington. The twin GRACE-FO spacecraft will measure and monitor monthly changes in how mass is redistributed within and among Earth's atmosphere, oceans, land and ice sheets, as well as within Earth itself. Photo Credit: (NASA/Joel Kowsky)

Michael Watkins, GRACE-FO science lead and director of NASA's Jet Propulsion Laboratory, discusses the upcoming launch of the Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) mission, Monday, April 30, 2018 at NASA Headquarters in Washington. The twin GRACE-FO spacecraft will measure and monitor monthly changes in how mass is redistributed within and among Earth's atmosphere, oceans, land and ice sheets, as well as within Earth itself. Photo Credit: (NASA/Joel Kowsky)

Phil Morton, NASA GRACE-FO project manager at JPL, discusses the upcoming launch of the Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) mission, Monday, April 30, 2018 at NASA Headquarters in Washington. The twin GRACE-FO spacecraft will measure and monitor monthly changes in how mass is redistributed within and among Earth's atmosphere, oceans, land and ice sheets, as well as within Earth itself. Photo Credit: (NASA/Joel Kowsky)

David Jarrett, GRACE-FO program executive in the Earth Science Division at NASA Headquarters, left, and Phil Morton, NASA GRACE-FO project manager at JPL, discuss the upcoming launch of the Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) mission with Karen Fox of NASA's Office of Communications, Monday, April 30, 2018 at NASA Headquarters in Washington. The twin GRACE-FO spacecraft will measure and monitor monthly changes in how mass is redistributed within and among Earth's atmosphere, oceans, land and ice sheets, as well as within Earth itself. Photo Credit: (NASA/Joel Kowsky)

Karen Fox, of NASA's Office of Communications, right, discusses the upcoming launch of the Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) mission with Michael Watkins, GRACE-FO science lead and director of NASA's Jet Propulsion Laboratory, left, and Frank Webb, GRACE-FO project scientist at JPL, Monday, April 30, 2018 at NASA Headquarters in Washington. The twin GRACE-FO spacecraft will measure and monitor monthly changes in how mass is redistributed within and among Earth's atmosphere, oceans, land and ice sheets, as well as within Earth itself. Photo Credit: (NASA/Joel Kowsky)

A model of one of the twin Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) spacecraft is seen following a pre-launch briefing on the mission, Monday, April 30, 2018 at NASA Headquarters in Washington. The twin GRACE-FO spacecraft will measure and monitor monthly changes in how mass is redistributed within and among Earth's atmosphere, oceans, land and ice sheets, as well as within Earth itself. Photo Credit: (NASA/Joel Kowsky)

Illustration of the twin spacecraft of the NASA/German Research Centre for Geosciences (GFZ) Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) mission. GRACE-FO will continue tracking the evolution of Earth's water cycle by monitoring changes in the distribution of mass on Earth. https://photojournal.jpl.nasa.gov/catalog/PIA22441

Illustration of the twin spacecraft of the NASA/German Research Centre for Geosciences (GFZ) Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) mission. GRACE-FO will continue tracking the evolution of Earth's water cycle by monitoring changes in the distribution of mass on Earth. https://photojournal.jpl.nasa.gov/catalog/PIA22440

NASA Headquarters Public Affairs Officer Steve Cole, left, moderates the Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) mission prelaunch media briefing with David Jarrett, GRACE-FO program executive in the Earth Science Division at NASA Headquarters; Frank Webb, GRACE-FO project scientist at JPL; Frank Flechtner, GRACE-FO project manager for the German Research Centre for Geosciences (GFZ) in Potsdam, Germany; Phil Morton, NASA GRACE-FO project manager at JPL; and Capt. Jennifer Haden, weather officer, 30th Space Wing, Vandenberg Air Force Base, right, Monday, May 21, 2018, at Vandenberg Air Force Base in California. The twin GRACE-FO spacecraft 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. Photo Credit: (NASA/Bill Ingalls)

NASA Headquarters Public Affairs Officer Steve Cole, left, moderates the Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) mission prelaunch media briefing with David Jarrett, GRACE-FO program executive in the Earth Science Division at NASA Headquarters; Frank Webb, GRACE-FO project scientist at JPL; Frank Flechtner, GRACE-FO project manager for the German Research Centre for Geosciences (GFZ) in Potsdam, Germany; Phil Morton, NASA GRACE-FO project manager at JPL; and Capt. Jennifer Haden, weather officer, 30th Space Wing, Vandenberg Air Force Base, right, Monday, May 21, 2018, at Vandenberg Air Force Base in California. The twin GRACE-FO spacecraft 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. Photo Credit: (NASA/Bill Ingalls)

Illustration of the twin spacecraft of the NASA/German Research Centre for Geosciences (GFZ) Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) mission. GRACE-FO will continue tracking the evolution of Earth's water cycle by monitoring changes in the distribution of mass on Earth. https://photojournal.jpl.nasa.gov/catalog/PIA22446

Illustration of the twin spacecraft of the NASA/German Research Centre for Geosciences (GFZ) Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) mission. GRACE-FO will continue tracking the evolution of Earth's water cycle by monitoring changes in the distribution of mass on Earth. https://photojournal.jpl.nasa.gov/catalog/PIA22447

Illustration of the twin spacecraft of the NASA/German Research Centre for Geosciences (GFZ) Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) mission. GRACE-FO will continue tracking the evolution of Earth's water cycle by monitoring changes in the distribution of mass on Earth. https://photojournal.jpl.nasa.gov/catalog/PIA22445

Frank Webb, GRACE-FO project scientist at JPL, left, and \Frank Flechtner, discuss the Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) mission during a prelaunch media briefing, Monday, May 21, 2018, at Vandenberg Air Force Base in California. The twin GRACE-FO spacecraft 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. Photo Credit: (NASA/Bill Ingalls)

David Jarrett, GRACE-FO program executive in the Earth Science Division at NASA Headquarters is seen during a Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) mission prelaunch media briefing, Monday, May 21, 2018, at Vandenberg Air Force Base in California. The twin GRACE-FO spacecraft 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. Photo Credit: (NASA/Bill Ingalls)

Frank Webb, GRACE-FO project scientist at JPL, discusses the Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) mission during a prelaunch media briefing, Monday, May 21, 2018, at Vandenberg Air Force Base in California. The twin GRACE-FO spacecraft 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. Photo Credit: (NASA/Bill Ingalls)

Phil Morton, NASA GRACE-FO project manager at JPL, discusses the Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) mission during a prelaunch media briefing, Monday, May 21, 2018, at Vandenberg Air Force Base in California. The twin GRACE-FO spacecraft 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. Photo Credit: (NASA/Bill Ingalls)

Phil Morton, NASA GRACE-FO project manager at JPL discusses the Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) mission during a prelaunch media briefing, Monday, May 21, 2018, at Vandenberg Air Force Base in California. The twin GRACE-FO spacecraft 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. Photo Credit: (NASA/Bill Ingalls)

Frank Flechtner, GRACE-FO project manager for the German Research Centre for Geosciences (GFZ) in Potsdam, Germany, discusses the Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) mission during a prelaunch media briefing, Monday, May 21, 2018, at Vandenberg Air Force Base in California. The twin GRACE-FO spacecraft 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. Photo Credit: (NASA/Bill Ingalls)

Phil Morton, NASA GRACE-FO project manager at JPL, second from right, discusses the Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) mission during a prelaunch media briefing, Monday, May 21, 2018, at Vandenberg Air Force Base in California. The twin GRACE-FO spacecraft 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. Photo Credit: (NASA/Bill Ingalls)

Frank Flechtner, GRACE-FO project manager for the German Research Centre for Geosciences (GFZ) in Potsdam, Germany, discusses the Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) mission during a prelaunch media briefing, Monday, May 21, 2018, at Vandenberg Air Force Base in California. The twin GRACE-FO spacecraft 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. Photo Credit: (NASA/Bill Ingalls)

David Jarrett, GRACE-FO program executive in the Earth Science Division at NASA Headquarters, discusses the Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) mission during a prelaunch media briefing, Monday, May 21, 2018, at Vandenberg Air Force Base in California. The twin GRACE-FO spacecraft 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. Photo Credit: (NASA/Bill Ingalls)

Experts discuss the Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) mission during a prelaunch media briefing, Monday, May 21, 2018, at Vandenberg Air Force Base in California. The twin GRACE-FO spacecraft 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. Photo Credit: (NASA/Bill Ingalls)

A graphic is shown as experts discuss the Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) mission during a prelaunch media briefing, Monday, May 21, 2018, at Vandenberg Air Force Base in California. The twin GRACE-FO spacecraft 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. Photo Credit: (NASA/Bill Ingalls)

A graphic is shown as experts discuss the Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) mission during a prelaunch media briefing, Monday, May 21, 2018, at Vandenberg Air Force Base in California. The twin GRACE-FO spacecraft 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. Photo Credit: (NASA/Bill Ingalls)

A photo showing the The twin GRACE-FO spacecraft installed on top of the five Iridium NEXT communications satellites is seen as experts discuss the Gravity Recovery and Climate Experiment Follow-On mission during a prelaunch media briefing, Monday, May 21, 2018, at Vandenberg Air Force Base in California. The twin GRACE-FO spacecraft 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. Photo Credit: (NASA/Bill Ingalls)

Capt. Jennifer Haden, weather officer, 30th Space Wing, Vandenberg Air Force Base, discusses the weather forecast during a Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) mission prelaunch media briefing, Monday, May 21, 2018, at Vandenberg Air Force Base in California. The twin GRACE-FO spacecraft 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. Photo Credit: (NASA/Bill Ingalls)

NASA Headquarters Public Affairs Officer Steve Cole moderates a Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) mission prelaunch media briefing, Monday, May 21, 2018, at Vandenberg Air Force Base in California. The twin GRACE-FO spacecraft 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. Photo Credit: (NASA/Bill Ingalls)

At the Harris Spaceport Systems facility at Vandenberg Air Force Base in California, the twin GRACE-FO satellites are integrated with the multi-satellite dispenser structure that will be used to deploy the satellites during launch on the SpaceX Falcon 9 launch vehicle. https://photojournal.jpl.nasa.gov/catalog/PIA22444

GRACE-FO has completed its first mission phase and demonstrated the performance of the precise ranging system that enables its measurements of how mass migrates around Earth. Along the satellites' ground track (top), the inter-spacecraft distance between them changes as the mass distribution underneath (i.e., from mountains, etc.) varies. The small changes measured by the Microwave Ranging Instrument (middle) agree well with topographic features along the orbit (bottom). https://photojournal.jpl.nasa.gov/catalog/PIA22507

The NASA/German Research Centre for Geosciences GRACE Follow-On spacecraft launch onboard a SpaceX Falcon 9 rocket, Tuesday, May 22, 2018, from Space Launch Complex 4E at Vandenberg Air Force Base in California. 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. GRACE-FO is sharing its ride to orbit with five Iridium NEXT communications satellites as part of a commercial rideshare agreement. Photo Credit: (NASA/Bill Ingalls)

The NASA/German Research Centre for Geosciences GRACE Follow-On spacecraft launch onboard a SpaceX Falcon 9 rocket, Tuesday, May 22, 2018, from Space Launch Complex 4E at Vandenberg Air Force Base in California. 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. GRACE-FO is sharing its ride to orbit with five Iridium NEXT communications satellites as part of a commercial rideshare agreement. Photo Credit: (NASA/Bill Ingalls)

The NASA/German Research Centre for Geosciences GRACE Follow-On spacecraft launch onboard a SpaceX Falcon 9 rocket, Tuesday, May 22, 2018, from Space Launch Complex 4E at Vandenberg Air Force Base in California. 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. GRACE-FO is sharing its ride to orbit with five Iridium NEXT communications satellites as part of a commercial rideshare agreement. Photo Credit: (NASA/Bill Ingalls)

The NASA/German Research Centre for Geosciences GRACE Follow-On spacecraft launch onboard a SpaceX Falcon 9 rocket, Tuesday, May 22, 2018, from Space Launch Complex 4E at Vandenberg Air Force Base in California. 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. GRACE-FO is sharing its ride to orbit with five Iridium NEXT communications satellites as part of a commercial rideshare agreement. Photo Credit: (NASA/Bill Ingalls)

The SpaceX Falcon 9 rocket is seen with the NASA/German Research Centre for Geosciences GRACE Follow-On spacecraft onboard, Monday, May 21, 2018, at Space Launch Complex 4E at Vandenberg Air Force Base in California. 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. GRACE-FO is sharing its ride to orbit with five Iridium NEXT communications satellites as part of a commercial rideshare agreement. Photo Credit: (NASA/Bill Ingalls)

The NASA/German Research Centre for Geosciences GRACE Follow-On spacecraft launch onboard a SpaceX Falcon 9 rocket, Tuesday, May 22, 2018, from Space Launch Complex 4E at Vandenberg Air Force Base in California. 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. GRACE-FO is sharing its ride to orbit with five Iridium NEXT communications satellites as part of a commercial rideshare agreement. Photo Credit: (NASA/Bill Ingalls)

The SpaceX Falcon 9 rocket is seen with the NASA/German Research Centre for Geosciences GRACE Follow-On spacecraft onboard, Tuesday, May 22, 2018, at Space Launch Complex 4E at Vandenberg Air Force Base in California. 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. GRACE-FO is sharing its ride to orbit with five Iridium NEXT communications satellites as part of a commercial rideshare agreement. Photo Credit: (NASA/Bill Ingalls)

The NASA/German Research Centre for Geosciences GRACE Follow-On spacecraft launch onboard a SpaceX Falcon 9 rocket, Tuesday, May 22, 2018, from Space Launch Complex 4E at Vandenberg Air Force Base in California. 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. GRACE-FO is sharing its ride to orbit with five Iridium NEXT communications satellites as part of a commercial rideshare agreement. Photo Credit: (NASA/Bill Ingalls)

The NASA/German Research Centre for Geosciences GRACE Follow-On spacecraft launch onboard a SpaceX Falcon 9 rocket, Tuesday, May 22, 2018, from Space Launch Complex 4E at Vandenberg Air Force Base in California. 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. GRACE-FO is sharing its ride to orbit with five Iridium NEXT communications satellites as part of a commercial rideshare agreement. Photo Credit: (NASA/Bill Ingalls)

The NASA/German Research Centre for Geosciences GRACE Follow-On spacecraft launch onboard a SpaceX Falcon 9 rocket, Tuesday, May 22, 2018, from Space Launch Complex 4E at Vandenberg Air Force Base in California. 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. GRACE-FO is sharing its ride to orbit with five Iridium NEXT communications satellites as part of a commercial rideshare agreement. Photo Credit: (NASA/Bill Ingalls)

The SpaceX Falcon 9 rocket is seen with the NASA/German Research Centre for Geosciences GRACE Follow-On spacecraft onboard, Monday, May 21, 2018, at Space Launch Complex 4E at Vandenberg Air Force Base in California. 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. GRACE-FO is sharing its ride to orbit with five Iridium NEXT communications satellites as part of a commercial rideshare agreement. Photo Credit: (NASA/Bill Ingalls)

The NASA/German Research Centre for Geosciences GRACE Follow-On spacecraft launch onboard a SpaceX Falcon 9 rocket, Tuesday, May 22, 2018, from Space Launch Complex 4E at Vandenberg Air Force Base in California. 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. GRACE-FO is sharing its ride to orbit with five Iridium NEXT communications satellites as part of a commercial rideshare agreement. Photo Credit: (NASA/Bill Ingalls)

The NASA/German Research Centre for Geosciences GRACE Follow-On spacecraft launch onboard a SpaceX Falcon 9 rocket, Tuesday, May 22, 2018, from Space Launch Complex 4E at Vandenberg Air Force Base in California. 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. GRACE-FO is sharing its ride to orbit with five Iridium NEXT communications satellites as part of a commercial rideshare agreement. Photo Credit: (NASA/Bill Ingalls)

The NASA/German Research Centre for Geosciences GRACE Follow-On spacecraft launch onboard a SpaceX Falcon 9 rocket, Tuesday, May 22, 2018, from Space Launch Complex 4E at Vandenberg Air Force Base in California. 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. GRACE-FO is sharing its ride to orbit with five Iridium NEXT communications satellites as part of a commercial rideshare agreement. Photo Credit: (NASA/Bill Ingalls)

Long exposure photograph showing the NASA/German Research Centre for Geosciences GRACE Follow-On spacecraft launching onboard a SpaceX Falcon 9 rocket, Tuesday, May 22, 2018, from Space Launch Complex 4E at Vandenberg Air Force Base in California. 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. GRACE-FO is sharing its ride to orbit with five Iridium NEXT communications satellites as part of a commercial rideshare agreement. Photo Credit: (NASA/Bill Ingalls)

The NASA/German Research Centre for Geosciences GRACE Follow-On spacecraft launch onboard a SpaceX Falcon 9 rocket, Tuesday, May 22, 2018, from Space Launch Complex 4E at Vandenberg Air Force Base in California. 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. GRACE-FO is sharing its ride to orbit with five Iridium NEXT communications satellites as part of a commercial rideshare agreement. Photo Credit: (NASA/Bill Ingalls)

The NASA/German Research Centre for Geosciences GRACE Follow-On spacecraft launch onboard a SpaceX Falcon 9 rocket, Tuesday, May 22, 2018, from Space Launch Complex 4E at Vandenberg Air Force Base in California. 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. GRACE-FO is sharing its ride to orbit with five Iridium NEXT communications satellites as part of a commercial rideshare agreement. Photo Credit: (NASA/Bill Ingalls)

The SpaceX Falcon 9 rocket is seen with the NASA/German Research Centre for Geosciences GRACE Follow-On spacecraft onboard, Monday, May 21, 2018, at Space Launch Complex 4E at Vandenberg Air Force Base in California. 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. GRACE-FO is sharing its ride to orbit with five Iridium NEXT communications satellites as part of a commercial rideshare agreement. Photo Credit: (NASA/Bill Ingalls)

The NASA/German Research Centre for Geosciences GRACE Follow-On spacecraft launch onboard a SpaceX Falcon 9 rocket, Tuesday, May 22, 2018, from Space Launch Complex 4E at Vandenberg Air Force Base in California. 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. GRACE-FO is sharing its ride to orbit with five Iridium NEXT communications satellites as part of a commercial rideshare agreement. Photo Credit: (NASA/Bill Ingalls)

The NASA/German Research Centre for Geosciences GRACE Follow-On spacecraft launch onboard a SpaceX Falcon 9 rocket, Tuesday, May 22, 2018, from Space Launch Complex 4E at Vandenberg Air Force Base in California. 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. GRACE-FO is sharing its ride to orbit with five Iridium NEXT communications satellites as part of a commercial rideshare agreement. Photo Credit: (NASA/Bill Ingalls)

The SpaceX Falcon 9 rocket is seen with the NASA/German Research Centre for Geosciences GRACE Follow-On spacecraft onboard, Monday, May 21, 2018, at Space Launch Complex 4E at Vandenberg Air Force Base in California. 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. GRACE-FO is sharing its ride to orbit with five Iridium NEXT communications satellites as part of a commercial rideshare agreement. Photo Credit: (NASA/Bill Ingalls)

The SpaceX Falcon 9 rocket is seen with the NASA/German Research Centre for Geosciences GRACE Follow-On spacecraft onboard, Tuesday, May 22, 2018, at Space Launch Complex 4E at Vandenberg Air Force Base in California. 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. GRACE-FO is sharing its ride to orbit with five Iridium NEXT communications satellites as part of a commercial rideshare agreement. Photo Credit: (NASA/Bill Ingalls)

The NASA/German Research Centre for Geosciences GRACE Follow-On spacecraft launch onboard a SpaceX Falcon 9 rocket, Tuesday, May 22, 2018, from Space Launch Complex 4E at Vandenberg Air Force Base in California. 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. GRACE-FO is sharing its ride to orbit with five Iridium NEXT communications satellites as part of a commercial rideshare agreement. Photo Credit: (NASA/Bill Ingalls)

Almost all of Greenland continued to lose mass in May 2019 as the ice sheet continues to melt. https://photojournal.jpl.nasa.gov/catalog/PIA23340

At the Harris Spaceport Systems facility at Vandenberg Air Force Base in California, the twin GRACE-FO satellites are integrated with the multi-satellite dispenser structure that will be used to deploy the satellites during launch on the SpaceX Falcon 9 launch vehicle. https://photojournal.jpl.nasa.gov/catalog/PIA22442

North America was almost entirely above its long-term average in mass in May 2019, due to Midwestern flooding, with the runoff raising the Great Lakes to record levels. https://photojournal.jpl.nasa.gov/catalog/PIA22840

Technicians inspect the twin GRACE Follow-On satellites and their multi-satellite dispenser at the SpaceX facility at Vandenberg Air Force Base in California. The satellites were subsequently stacked atop another satellite dispenser containing the five Iridium NEXT communications satellites they will share a ride to orbit with. https://photojournal.jpl.nasa.gov/catalog/PIA22452