GRACE Follow-On

GRACE Follow-On observes critical indicators of climate change through changes in Earth's gravitational field with LISA technology. The mission uses a laser interferometer between two satellites with nanometre-level accuracy.

GRACE

GRACE (Gravity Recovery And Climate Experiment, 2002-2017), was a joint US-German satellite mission that has provided new and unexpected insights into the natural processes of the Earth. In the GRACE mission, the distance between two spacecraft was measured using a microwave ranging system. Temporal estimates of the Earth's gravity field are inferred from changes in this distance. The changes in Earth's gravity field in turn can be used to measure indicators of climate change – like melting polar ice or changes in groundwater levels.

GRACE Follow-On

The GRACE Follow-On mission (GRACE FO, 2018-today) reflies the identical GRACE spacecraft and instruments, but supplements the micrometre-level accuracy microwave measurement with a laser interferometer with nanometre-level accuracy.

The laser interferometer demonstrator on GRACE Follow-On is a partnership between NASA, which provides the laser, cavity assembly, and ranging processor, the German Research Center for Geosciences (GFZ), and the Albert Einstein Institute, which is responsible for and overseeing the laser ranging instrument and in particular the measurement optics and steering mirror assembly along with instrument integration and testing.

The mission was successfully launched into Earth orbit on May 22, 2018. First observational data were received in the summer of 2018. Since then, the system has been running reliably and has been delivering high-precision distance measurements in scientific data taking mode.

LISA technology in an Earth orbit

For monitoring the Earth gravitational field LISA Pathfinder technology is employed: The LISA phasemeter was adapted to the needs of the gravity field mapping mission.

Under this project a consortium of U.S. and German institutions produced hardware for the laser ranging interferometer flying on the GRACE Follow-On mission. This system improved the inter-satellite ranging sensitivity by a factor of 200 over the initial GRACE mission.

Preparing the next geodesy satellites

In the future, two orbiting satellite missions could measure the Earth's gravitational field and how it changes even more precisely.

GRACE-I is a joint project of the Helmholtz Association, NASA, DLR, and the Max Planck Society. The pair of identical satellites, will fly in an Earth orbit significantly lower than GRACE Follow-On. This will allow it to monitor changes in the Earth's gravitational field and the global water cycle with unprecedented accuracy.

The European Space Agency ESA is currently planning a “Next Generation Gravity Mission” (NGGM) which will consist of a GRACE-like pair of satellites in an orbit lower than and inclined to that of GRACE-like missions. By combining the data from both missions in the “Mass-Change and Geosciences International Constellation” (MAGIC) project, the measurement accuracy of changes in the Earth's gravitational field – both in time and in space – will be significantly improved.

Because of their expertise, AEI researchers are involved in the design of the laser interferometers used in both projects.

GRACE Follow-On News

Successful German-US environmental mission to be continued with GRACE-C

The next generation of the satellite pair will use a high-precision laser instrument with key contributions from the AEI Hannover to monitor indicators of climate change. more

20 years ago: Launch of the GRACE geodesy mission

Anniversary event at the GFZ German Research Centre for Geosciences looks back and towards the future more

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Scientific literature

Misfeldt, M. M.; Bekal , P.; Müller, V.; Heinzel, G.: Disturbances from Single Event Upsets in the GRACE Follow-On Laser Ranging Interferometer. Advances in Space Research 72 (6), pp. 2259 - 2269 (2023)
Misfeldt, M. M.; Müller, V.; Müller, L.; Wegener, H.; Heinzel, G.: Scale Factor Determination for the GRACE-Follow On Laser Ranging Interferometer including Thermal Coupling. Remote Sensing 15 (3), 570 (2023)
Müller, V.; Hauk, M.; Misfeldt, M. M.; Müller, L.; Wegener, H.; Yan, Y.; Heinzel, G.: Comparing GRACE-FO KBR and LRI ranging data with focus on carrier frequency variations. Remote Sensing 14 (17), 4335 (2022)
Yan, Y.; Müller, V.; Heinzel, G.; Zhong, M.: Revisiting the Light Time Correction in Gravimetric Missions Like GRACE and GRACE Follow-On. Journal of Geodesy 95, 48 (2021)
Wegener, H.; Müller, V.; Heinzel, G.; Misfeldt, M.: Tilt-to-Length Coupling in the GRACE Follow-On Laser Ranging Interferometer. Journal of Spacecraft and Rockets 57 (6), pp. 1362 - 1372 (2020)
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