Lori Magruder, University of Texas at Austin, ICESat-2 science definition team lead, 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).