Earth System MassTransport Mission

Proposal for new ESA Earth Explorer Satellite Mission

Observing the gravity field of the Earth from space is the only available tool to observe and monitor mass distribution and mass transport in the system Earth consistently and globally. Such observations enable the quantification of the global water cycle budget, which includes for example ground water monitoring, melting of polar ice caps and deglaciation, river run-offs and many others. In addition the modelling of lithospheric processes in solid Earth physics and determination of ocean circulation are other major applications. The value of such observations was proven by the ESA’s GOCE mission and the joint NASA/DLR GRACE satellites during the last decade. The success of these missions triggered the realization of another a joint US/German mission (GRACE Follow-On) to be launched in 2018, which is designed to continue the observation of mass transport with the same spatial and temporal resolutions.

Since many years the chair of Astronomical and Physical Geodesy is involved in these activities and specifically works on future concepts for observing mass transport in the system Earth. In recent projects performed for the European Space Agency (ESA), it was identified that a so-called Bender constellation of two satellite pairs flying in different inclined orbits (one near polar and another inclined satellite pair) can fulfil the requirements of Earth science disciplines asking for mass transport observations with higher temporal and spatial resolutions as it can be achieved nowadays. Each pair observes changes of their inter-satellite distances with a few 10’s of nanometre precision by making use of a newly developed laser interferometer. Non-gravitational accelerations, which are disturbing the gravitational signal, are measured with electrostatic space accelerometers at the level of 10-11 m/s2 precision.

This concept was recently proposed by a larger group of European scientists with the support of technological and industrial partners and under coordination of the Chair of Astronomical and Physical Geodesy (who acts as lead proposer) as Earth Explorer 9 mission to ESA. The name of this mission is e.motion2 (Earth System Mass Transport Mission – Square). Depending on the constellation mass transport can be observed with factor of 5 to 50 increased sensitivity with respect to nowadays knowledge. In addition such constellations offer the possibility to observe daily mass transport in the Earth system, which is an important observable for atmospheric modelling, and operational services, e.g., for water management and groundwater monitoring as well as forecasting of floods and droughts.