Both GRACE and GOCE have proven to be very successful missions, providing a wealth
of data which are exploited for geophysical studies such as climate changes, hydrology,
sea level changes, solid Earth phenomena, with benefits for society and the whole world
population. It is indispensable to continue monitoring gravity and its changes from space,
so much so that a GRACE follow-on mission has been launched in 2018. In this paper, a
new satellite mission concept named MOCASS is presented, which can be considered as a
GOCE follow-on, based on an innovative gradiometer exploiting ultra-cold atom technology
and aimed at monitoring Earth mass distribution and its variations in time. The technical
aspects regarding the payload will be described, illustrating the measurement principle
and the technological characteristics of a cold atom interferometer that can measure gravity
gradients. The results of numerical simulations will be presented for a one-arm and a
two-arm gradiometer and for different orbit configurations, showing that an improvement
with respect to GOCE could be obtained in the estimate of the static gravity field over
all the harmonic spectrum (with an expected error of the order of 1 mGal at degree 300
for a 5-year mission) and that estimates are promising also for the time-variable gravity
field (although GRACE is still performing better at very low degrees). Finally, the progress
achievable by exploiting MOCASS observations for the detection and monitoring
of geophysical phenomena will be discussed: the results of simulations of key geophysical
themes (such as mass changes due to hydrology, glaciers and tectonic effects) with
expected gravity change-rates, time constants and corresponding wavelengths, show that an
improvement is attainable and that signals invisible to past satellites could be detected by
exploiting the cold atom technology.
