The Innovative Acquisition and Pointing Metrology for Next Generation Gravity Mission

The measurement of static and temporal variation of Earth's gravity field provides an insight on water storage, seasonal and sub-seasonal water cycles, their impact on water levels, and delivers key data to Earth's climate models. After missions like GOCE (ESA), GRACE and GRACE Follow-On (US-DE), ESA is studying a new mission provisionally named “Next Generation Gravity Mission” (NGGM) consisting of two pairs of satellites and a heterodyne laser interferometer for intersatellite ranging. Currently, two laser ranging interferometer concepts are under evaluation: the transponder and the retroreflector concept. Both concepts require to perform the laser link acquisition via an auxiliary optical metrology, named Acquisition and Pointing Metrology System (APMS). It is composed by a light source (mounted on one out of the two satellites) and an acquisition detector (mounted on the counterpart satellite). This paper describes the recently performed activity related to breadboarding and testing of the APMS optical head.