As changes in gravity are directly related to massvariability, satellite missions observing the Earth’s timevarying gravity eld are a unique tool for observing masstransport processes in the Earth system, such as the watercycle, rapid changes in the cryosphere, oceans, andsolid Earth processes, on a global scale. The observationof Earth’s gravity eld was successfully performed by theGRACE and GOCE satellite missions, and will be continuedby the GRACE Follow-On mission. A comprehensiveteam of European scientists proposed the next-generationgravity eld mission MOBILE in response to the EuropeanSpace Agency (ESA) call for a Core Mission in theframe of Earth Explorer 10 (EE10). MOBILE is based onthe innovative observational concept of a high-low trackingformation with micrometer ranging accuracy, complementedby new instrument concepts. Since a high-lowtracking mission primarily observes the radial componentof gravity-induced orbit perturbations, the error structureis close to isotropic. This geometry signi cantly reducesartefacts of previous along-track ranging low-low formations(GRACE, GRACE-Follow-On) such as the typical stripingpatterns. The minimum con guration consists of atleast two medium-Earth orbiters (MEOs) at 10000 km altitudeor higher, and one low-Earth orbiter (LEO) at 350-400 km. The main instrument is a laser-based distance ordistance change measurement system, which is placed atthe LEO. TheMEOs are equipped either with passive re ectorsor transponders. In a numerical closed-loop simulation,itwas demonstrated that this minimum con gurationis in agreement with the threshold science requirements of5 mm equivalent water height (EWH) accuracy at 400 kmwavelength, and 10 cm EWH at 200 km. MOBILE providespromising potential future perspectives by linking the conceptto existing space infrastructure such as Galileo nextgeneration,as future element of the Copernicus/Sentinelprogramme, and holds the potential of miniaturization even up to swarm con gurations. As such MOBILE can beconsidered as a precursor and role model for a sustainedmass transport observing system from space.