As changes in gravity are directly related to mass
variability, satellite missions observing the Earth’s time
varying gravity eld are a unique tool for observing mass
transport processes in the Earth system, such as the water
cycle, rapid changes in the cryosphere, oceans, and
solid Earth processes, on a global scale. The observation
of Earth’s gravity eld was successfully performed by the
GRACE and GOCE satellite missions, and will be continued
by the GRACE Follow-On mission. A comprehensive
team of European scientists proposed the next-generation
gravity eld mission MOBILE in response to the European
Space Agency (ESA) call for a Core Mission in the
frame of Earth Explorer 10 (EE10). MOBILE is based on
the innovative observational concept of a high-low tracking
formation with micrometer ranging accuracy, complemented
by new instrument concepts. Since a high-low
tracking mission primarily observes the radial component
of gravity-induced orbit perturbations, the error structure
is close to isotropic. This geometry signi cantly reduces
artefacts of previous along-track ranging low-low formations
(GRACE, GRACE-Follow-On) such as the typical striping
patterns. The minimum con guration consists of at
least two medium-Earth orbiters (MEOs) at 10000 km altitude
or higher, and one low-Earth orbiter (LEO) at 350-
400 km. The main instrument is a laser-based distance or
distance change measurement system, which is placed at
the LEO. TheMEOs are equipped either with passive re ectors
or transponders. In a numerical closed-loop simulation,
itwas demonstrated that this minimum con guration
is in agreement with the threshold science requirements of
5 mm equivalent water height (EWH) accuracy at 400 km
wavelength, and 10 cm EWH at 200 km. MOBILE provides
promising potential future perspectives by linking the concept
to existing space infrastructure such as Galileo nextgeneration,
as future element of the Copernicus/Sentinel
programme, and holds the potential of miniaturization even up to swarm con gurations. As such MOBILE can be
considered as a precursor and role model for a sustained
mass transport observing system from space.
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