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, 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)

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)