NASA Scientist Michelle Thaller, Tom Wagner, ICESat-2 Program Scientist, NASA Headquarters, center, and Bill Barnhart, ICESat-2 Program Manager, Northrop Grumman, are seen during a NASA Ice, Cloud and land Elevation Satellite-2 (ICESat-2) prelaunch briefing, Thursday, Sept. 13, 2018, at Vandenberg Air Force Base in California. The ICESat-2 mission will measure the changing height of Earth's ice. Photo Credit: (NASA/Bill Ingalls)

Bill Barnhart, ICESat-2 Program Manager, Northrop Grumman, left, Doug McLennan, ICESat-2 Project Manager, NASA's Goddard Space Flight Center, center, and Cathy Richardson, Deputy Program Manager, Earth Science Projects Division, NASA's Goddard Space Flight Center, are seen during a NASA Ice, Cloud and land Elevation Satellite-2 (ICESat-2) prelaunch briefing, Thursday, Sept. 13, 2018, at Vandenberg Air Force Base in California. The ICESat-2 mission will measure the changing height of Earth's ice. Photo Credit: (NASA/Bill Ingalls)

Bill Barnhart, ICESat-2 program manager, Northrop Grumman, speaks to members of the news media and social media participants during a prelaunch mission briefing for NASA's Ice, Cloud and land Elevation Satellite-2 (ICESat-2), a mission to measure the changing height of Earth's ice, on Sept. 13, 2018 at Vandenberg Air Force Base (VAFB) in California. ICESat-2 will launch aboard a United Launch Alliance Delta II, the rocket’s final mission, from Space Launch Complex 2 at VAFB. Launch is scheduled for 8:46 a.m. EDT (5:46 a.m. PDT).