Abstract
The Gravity Recovery and Climate Experiment (GRACE) is a joint US/German mission that has been mapping the Earth's gravity field since 2002 by measuring the distance variations between two spacecraft using a micro-wave link. GRACE is reaching the end of its lifetime. For this reason and in order to minimize data gaps, an almost identical mission will be launched in 2017. This mission is called GRACE-Follow On (GRACE-FO) and it will include an additional instrument as a technological demonstrator to monitor distance changes between the spacecraft. This instrument is the Laser Ranging Interferometer (LRI), which is based on heterodyne laser interferometry at 1064 nm and takes advantage of many technologies developed for LISA. In this paper a short overview of the current status of the German contribution is presented.
Highlights
The Gravity Recovery and Climate Experiment (GRACE) mission has been measuring changes in the gravity field of the Earth since 2002 and has allowed the quantification of mass variations, such as the mass loss of polar ice sheets, the contribution of mass influx to sea level rise, and changes in the hydrological cycle [1]
For this reason and in order to minimize data gaps, an almost identical mission will be launched in 2017. This mission is called GRACE-Follow On (GRACE-FO) and it will include an additional instrument as a technological demonstrator to monitor distance changes between the spacecraft. This instrument is the Laser Ranging Interferometer (LRI), which is based on heterodyne laser interferometry at 1064 nm and takes advantage of many technologies developed for LISA
Triple Mirror Assembly The TMA is a large lateral offset (600 mm) retro-reflector composed of three orthogonal mirrors [9, 10] and is a key element for the LRI since: (i) it routes the beam around the microwave ranging instrument and the cold gas tanks; (ii) it keeps the incoming and outgoing beams anti-parallel and (iii) it allows to place its virtual vertex in the SC accelerometer reference point, and minimize SC jitter to path-length coupling, which is crucial due to the GRACE-FO low Earth orbit
Summary
The Gravity Recovery and Climate Experiment (GRACE) mission has been measuring changes in the gravity field of the Earth since 2002 and has allowed the quantification of mass variations, such as the mass loss of polar ice sheets, the contribution of mass influx to sea level rise, and changes in the hydrological cycle [1]. 2. Triple Mirror Assembly The TMA is a large lateral offset (600 mm) retro-reflector composed of three orthogonal mirrors [9, 10] and is a key element for the LRI since: (i) it routes the beam around the microwave ranging instrument and the cold gas tanks; (ii) it keeps the incoming and outgoing beams anti-parallel and (iii) it allows to place its virtual vertex in the SC accelerometer reference point, and minimize SC jitter to path-length coupling, which is crucial due to the GRACE-FO low Earth orbit. TMA Flight Models (FM) will go under performance and environmental tests in late 2014 and early 2015
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