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)