03.11.2016: In cooperation with the US space agency NASA, the GFZ runs the GRACE Follow-on (GRACE-FO) program. The objective of the corresponding satellite mission is to investigate the Earth’s gravity field. The launch of the mission is planned for the end of 2017. Now Airbus Defence and Space, the second largest aerospace company in the world, finalized the first of two satellites of the tandem-mission, built under subcontract of NASA’s Jet Propulsion Laboratory, JPL. The second satellite will follow in about four weeks.

The primary objective of the satellite mission GRACE-FO, the successor of the GRACE mission that is in orbit already since 2002, is to measure the Earth’s gravity field and its temporal variations. “GRACE” stands for „Gravity Recovery and Climate Experiment“. Two identically constructed satellites will circle the Earth within a distance of 220 kilometers to each other on a low polar orbit in a height of about 500 kilometers. The distance between the two satellites will be constantly measured by a microwave instrument with a precision of 0.002 millimeters. Any distance changes are subject to gravitation and allow for a precise modelling of the Earth’s gravity field. Throughout the entire mission of at least five years the measurements will provide an updated model of the field every 30 days. These time series serve to monitor indicators of climate change, like the melting of polar ice caps, sea level rise or changes in the global hydrologic cycle. The satellites further provide up to 200 daily atmospheric temperature and water vapour profiles.

For the first time, the satellite tandem is equipped with a Laser Ranging Interferometer (LRI). The LRI allows for measurements of the distance between the satellites way more precisely than via the microwave instrument. This technology demonstration serves as a preparation of future GRACE-like satellite missions.
Next, the satellite is delivered to Ottobrunn close to Munich, Germany, and tested for several months with regard to expected launch and space environment at the analysis and testing company IABG.

Within NASA the JPL is responsible for the realization of the GRACE FO project. The German contributions are managed by the GFZ and jointly funded by the Federal Ministry of Education and Research, the Federal Ministry of economics and Technology, the Helmholtz Association, the German Aerospace Center, and the GFZ. Frank Flechtner, head of the GFZ section Global Geomonitoring and Gravity Field, is the responsible project manager of the mission at the GFZ. According to the Memorandum of Understanding between NASA and the GFZ, the GFZ is responsible within the joint US-German Science Data System for the scientific data evaluation and distribution of the GRACE-FO products via the GFZ Information Systems and Data Center, for the manufacturing of the LRI, the launch services, provision of laser retro-reflectors for both satellites, the lead of the European science team, as well as the mission operations supported by the USA, subcontracted to the German Space Operations Center of the German Aerospace Center, DLR. (ak)

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