The laser ranging interferometer (LRI) onboard the GRACE Follow-On satellite mission had its “first light” on June 14, 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 the novel instrument and achieved success on first try.
The LRI measures the 220 kilometer distance between the two spacecraft with nanometer precision. Changes in the distance indicate changes in the mass below the twin satellites. GRACE-FO can thus measure Earth’s gravity as did the mission GRACE from 2002 to 2017. Measurements are carried out by microwave sensors. The LRI will add to the precision and is also an important milestone on the path towards LISA, the planned gravitational-wave observatory in space. (jz)