Earth System Mass Transport Mission (e.motion): A Concept for Future Earth Gravity Field Measurements from Space

In the last decade, satellite gravimetry has been revealed as a pioneering
technique for mapping mass redistributions within the Earth system. This fact has allowed
us to have an improved understanding of the dynamic processes that take place within andbetween the Earth’s various constituents. Results from the Gravity Recovery And Climate
Experiment (GRACE) mission have revolutionized Earth system research and have
established the necessity for future satellite gravity missions. In 2010, a comprehensive
team of European and Canadian scientists and industrial partners proposed the e.motion
(Earth system mass transport mission) concept to the European Space Agency. The proposal
is based on two tandem satellites in a pendulum orbit configuration at an altitude of
about 370 km, carrying a laser interferometer inter-satellite ranging instrument and
improved accelerometers. In this paper, we review and discuss a wide range of mass
signals related to the global water cycle and to solid Earth deformations that were outlined
in the e.motion proposal. The technological and mission challenges that need to be
addressed in order to detect these signals are emphasized within the context of the scientific
return. This analysis presents a broad perspective on the value and need for future satellite
gravimetry missions.