A core mission of the European Space Agency’s Earth Explorer Program that aims to provide new understanding of the physics of the Earth’s interior, including geodynamics associated with the lithosphere, mantle composition and rheology, and uplifting and subduction processes, measurements to permit a precise estimate of the marine geoid and combined with satellite altimetry of absolute ocean circulation and transport of mass, mapping of short-wavelength features of the dynamic topography to an accuracy of 1–2 cm on a global scale, identification of features of the geostrophic current field, estimation of the thickness of polar ice sheets, and to provide a highly accurate reference system for global heights. The satellite was launched on 17 March 2009, from Plesetsk, Russia, into a Sun-synchronous circular orbit at an altitude of 250–270 km.