After a successful year-long test programme by Airbus (www.airbus.com) at IABG in Ottobrunn (near Munich), the twin GRACE-FO (Gravity Recovery and Climate Experiment Follow-On) satellites will soon travel to their launch site in California.

During testing, the gravity-measuring satellites (they will track the continuous movement of water, ice and the solid Earth due to the Earth’s changing seasons, weather and climate processes, earthquakes and even human activities) were subjected to conditions similar to those they will experience during launch and in low Earth orbit.

Both satellites, each weighing 600kg, will be flown to the Vandenberg Air Force Base launch site (in California) in
December for final launch preparations.

The project is a partnership between NASA’s Jet Propulsion Laboratory (in Pasadena, California) and the German Research Centre for Geosciences (GFZ in Potsdam).

Both GRACE-FO research satellites will be launched into polar orbit sat an altitude of around 500km and 220km apart. They will then take continuous and very precise measurements of the distance variations between each other and make monthly maps of the changes in Earth’s gravitational field.

The launch of the GRACE-FO twin satellites is planned for spring 2018, and their mission is planned to last at least five years.

A Global Positioning System and a microwave ranging system will measure the distance between the satellites to within a few microns, while a sensitive accelerometer will account for non-gravitational effects, such as atmospheric drag and solar radiation.

The satellites will also feature an inter-satellite laser ranging instrument, developed by a German/American joint venture; it will be tested for use in future generations of gravitational research.