The satellite mission Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) has resumed collecting data.

A switchover to the backup system was required after an anomaly occurred on the Instrument Processing Unit (IPU) of the primary system of one of the satellites of the twin satellite mission: The primary unit was powered down on 19 July 2018 when an instrument fault monitor detected that the microwave instrument (MWI) was using less current than expected. After a detailed investigation by a team of NASA’s Jet Propulsion Laboratory, the backup IPU in the MWI was powered up on 19 Oct, successfully.

"The backup IPU is performing nominally and we have re-established satellite data collection”, says Frank Flechtner, GRACE-FO project manager and head of GFZ section Global Geomonitoring and Gravity Field.

After successfully completing the switchover to the backup system it still misses in-orbit checks. These will include calibrations and other system tests and are expected to continue until mid of January 2019, when GRACE-FO will enter the science phase of its mission.

The MWIs are the primary measurement instruments of the satellite mission. Via the MWIs the satellites very precisely measure distance changes between them. Based on these, changes in Earth’s gravity field are detected. Measurements of changes in Earth's gravity field indicate mass change and enable unique insights into Earth's changing climate, Earth system processes like droughts and sea level changes, and the impacts of human activities on water resources.
The primary science objective of GRACE-FO -- like that of its predecessor mission GRACE, which operated from 2002 to 2017 - is to track how water is redistributed on Earth by producing highly accurate, monthly gravity field maps.

GRACE-FO is a partnership between GFZ and NASA. The spacecrafts are operated from the German Space Operations Center in Oberpfaffenhofen, Germany, under a GFZ contract with the German Aerospace Center. JPL manages the mission for NASA's Science Mission Directorate at NASA's Headquarter in Washington. Caltech in Pasadena, California, manages JPL for NASA. (ak)

More information:
https://www.nasa.gov/gracefo
https://gracefo.jpl.nasa.gov/