First light for GRACE Follow-On laser interferometer

For the first time, laser interferometry between two satellites in space measures their 220-kilometer distance to nanometer precision

July 02, 2018

The laser ranging interferometer (LRI), a novel instrument onboard the GRACE Follow-On satellite mission, had its “first light” on 14th June 2018. An international team of researchers from the German Max Planck Institute for Gravitational Physics (Albert Einstein Institute, AEI) in Hannover, the Leibniz Universität Hannover, and the NASA Jet Propulsion Laboratory switched on their instrument and achieved success on first try. Since then, the LRI has been taking scientific measurements in parallel to the main microwave ranging instrument. Initial results agree well, and the research team is optimistic that the LRI’s improved precision will assist in tracking indicators of climate change by observing Earth’s gravity field and its variations. GRACE Follow-On is a joint project of NASA with German partners, which are led by the GFZ German Research Centre for Geosciences. The success is also an important milestone on the path towards LISA, the planned gravitational-wave observatory in space.

Background information

GRACE Follow-On is a joint project of NASA and German partners led by the GFZ German Research Centre for Geosciences. It is the improved successor to the successful GRACE mission which operated from 2002 to 2017.

The LRI is a cooperation between NASA and German partners, with the German contribution led by the AEI. In Germany, the LRI concept, its prototypes and technical specifications were done at the AEI. AEI researchers have been heavily involved in developing and testing the flight hardware. The development of the LRI is based on a longstanding partnership between AEI and NASA’s Jet Propulsion Laboratory. If the laser instrument stands the test future missions could rely solely on the more precise laser interferometers instead of microwave interferometers.

The German contributions to the LRI include the entire optical system, consisting of a steering mirror, built by Hensoldt (previously Zeiss) in Oberkochen and the optical bench from SpaceTech GmbH in Immenstaad, opto-electronics from the German Aerospace Center (DLR) in Berlin-Adlershof, and electronic systems from Apcon AeroSpace & Defence in Neubiberg near Munich. SpaceTech GmbH is responsible for the industrial part of the entire German LRI contribution. The DLR Institute of Space Systems in Bremen developed and delivered calibration and testing instruments. Both satellites were built on behalf of NASA by Airbus in Friedrichshafen. Mission control for GRACE Follow-On is provided by the German Space Operations Centre (GSOC) in Oberpfaffenhofen near Munich under subcontract of GFZ.

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