Launch preparations for GRACE-FO geosciences satellites. Technicians inspecting the twin GRACE Follow-On satellites and their multi-satellite dispenser at the SpaceX facility at Vandenberg Air Force Base in California, USA. The Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) satellite is a partnership between NASA and the German Research Centre for Geosciences (GFZ). It consists of two twin spacecraft, enabling it to measure variations in gravity over the Earth's surface. GRACE-FO will track the evolution of Earth's water cycle by monitoring changes in the distribution of mass on Earth. It was launched on 22 May 2018. Image published on 11 May 2018.