28 October 2016 – Airbus Defence and Space, the world’s second largest space company, has finished construction of the first of the two GRACE-FO (GRACE = Gravity Recovery and Climate Experiment, FO = Follow-On) satellites in Friedrichshafen, Germany. The satellite will now be transferred to Ottobrunn near Munich for several months of operational testing in the IABG test centre.

NASA’s Jet Propulsion Laboratory JPL (Pasadena, California) will send both GRACE-FO research satellites into a polar orbit at an altitude of around 500 km and at a distance of 220 km apart. This is a follow-on to the GRACE mission, which has been successfully in operation since 2002. As they travel around the Earth, these satellites constantly take very exact measurements of their separation distance, which changes depending on the Earth’s gravity. In this way, scientists are able to map the Earth’s gravitational fields.

A global positioning system and a microwave ranging system enable the distance between the satellites to be measured to within one micron. The GRACE-FO satellites will feature an additional element: a new inter-satellite laser ranging instrument, developed by a German/American joint venture, which will be tested for use in future generations of gravitational research satellites.