GRACE-FO

Mission Specification

GRACE-FO twin satellites as seen in an artist's rendering
Credit: NASA

The Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) mission is a partnership between NASA and the German Research Centre for Geosciences (GFZ). GRACE-FO is a successor to the original GRACE mission, which began orbiting Earth on March 17, 2002. GRACE-FO will carry on the extremely successful work of its predecessor while testing a new technology designed to dramatically improve the already remarkable precision of its measurement system. The twin GRACE-FO satellites will follow each other in orbit around the Earth, separated by about 137 miles (220 km). 

GRACE-FO, scheduled for launch in 2018, will continue the work of tracking Earth's water movement to monitor changes in underground water storage, the amount of water in large lakes and rivers, soil moisture, ice sheets and glaciers, and sea level caused by the addition of water to the ocean. These discoveries provide a unique view of Earth's climate and have far-reaching benefits to society and the world's population.

How it works

GRACE-FO's raw data will be a series of measurements showing how the distance between the two satellites varies as they orbit Earth. The twin GRACE satellites follow each other in orbit around the Earth, separated by about 137 miles (220 km). They constantly send microwave signals to each other to track the distance variation (down to about one-millionth of a meter) between them.

As the pair circles the Earth, areas of slightly stronger gravity (greater mass concentration) affect the lead satellite first, pulling it away from the trailing satellite. As the satellites continue, the trailing satellite is pulled toward the lead satellite as it passes over the gravity anomaly. The change in distance would certainly be imperceptible to our eyes, but the extremely precise microwave ranging system on GRACE-FO detects minuscule changes in the distance between the satellites. A highly accurate measuring device known as an accelerometer, located at each satellite’s center of mass, measures the non-gravitational accelerations (such as those due to atmospheric drag) so that only accelerations caused by gravity are considered. Satellite Global Positioning System (GPS) receivers determine the exact position of the satellite over the Earth to within a centimeter or less. All this information from the satellites is used to construct monthly maps of the Earth’s average gravity field, offering details of how mass, in most cases water, is moving around the planet.

GRACE-FO data products

The GRACE-FO mission will continually generate the full records of Level 1, Level 2 and Level 3 products which are listed in table below by three key partners​.  All GRACE-FO products are managed and distributed through the PO.DAAC data center. To promote the GRACE-FO data interoperability, all products are produced in either standard netCDF and/or ASCII YAML format, in compliance with PO.DAAC data best practices and NASA ESDIS metadata standards. Different from GRACE ASCII files, GRACE-FO ASCII files have been redesigned with its header constructed in the YAML format. 

GRACE-FO Standard Products Table (in work)