Measuring Earth: Current status of the GRACE Follow-On Laser Ranging Interferometer

The GRACE mission that was launched in 2002 has impressively proven the feasibility of low-orbit satellite-to-satellite tracking for Earth gravity observations. Especially mass transport related to Earth's hydrological system could be well resolved both spatially and temporally. This allows to study processes such as polar ice sheet decline and ground water depletion in great detail. Owing to GRACE's success, NASA and GFZ will launch the successor mission GRACE Follow-On in 2017. In addition to the microwave ranging system, GRACE Follow-On will be the first mission to use a Laser Ranging Interferometer as technology demonstrator to track intersatellite distance changes with unprecedented precision. This new ranging device inherits some of the technologies which have been developed for the future spaceborne gravitational wave detector LISA. I will present the architecture of the Laser Ranging Interferometer, point out similarities and differences to LISA, and conclude with the current status of the flight hardware production. Figure 1. Artistic view of the GRACE Follow-On satellites. The microwave beam is shown in blue, the laser beams in red. Watch a brief animation about GRACE Follow-On and the Laser Ranging Interferometer by scanning the QR code or by going to www.gracefo.spacegravity.org/video1. Image credit: Satellites: AEI/Daniel Schütze, Earth: NASA