Gravity Recovery And Climate Experiment

The twin satellite Gravity Recovery And Climate Experiment ( GRACE ) is a project for the accurate determination of the Earth's gravity field in a low orbit. Due to their correlated orbit satellites were given the nickname " Tom" and "Jerry". The GRACE satellites are the successor of the predecessor mission CHAMP, which was launched in 2000. They are based on the model developed by Astrium flexbus concept that enables an extremely cost-effective and rapid production of the satellites.

The satellites were launched on 17 March 2002 for a Rokot rocket from Plesetsk into a near -polar (inclination = 89 ° ) and circular orbit with a Anfängshöhe of 500 km. The satellites operate on the principle SST (Satellite -to- Satellite Tracking ): they fly around the world on the same path in 200 km distance and measure with microwaves continuously mutual distance. This irregularity of the gravity field with high precision can be analyzed, although the gravity anomalies in a few hundred kilometers above already account for significantly less than at the surface.

When a satellite, for example, a region approaches with increased gravity, he becomes slightly accelerated ( compared to an unperturbed orbit ) and the satellite spacing increases. Where the second satellite at this point, the distance will thus typically.

The project was developed by DLR and NASA / JPL in cooperation and promises in a few years a knowledge of the global geoid to about a centimeter - about five to ten times more accurately than with previous methods of satellite geodesy. However, the spatial resolution due to the altitude of about 470 km to 150 km is limited, so that flight and terrestrial gravimetry and the geoid determination astrogeodätische not yet unnecessary. Along with the latter, the geoid could be / is determined in a few years and regionally locally on centimeter accuracy; would be necessary in order to fully exploit the potential of geoscientific dGPS.

The scientific evaluation is carried out at the University of Texas CSR and the Research Centre for Geosciences (GFZ ).

GRACE also makes it possible to determine changes of the geoid with high precision from the accumulated data. This coming new aspects of Geodynamics and independent investigation methods for oceanography and possibly climate change to the attention of scientists. A comparison of the data with those of the started in March 2009 gradiometry satellite GOCE is in progress.

The measured data from GRACE showed that the Antarctic ice mass has decreased within 3 years to about 150 cubic kilometers, which corresponds to an increase in sea level by 0.4 mm per year. Also, changes in quantity of groundwater could be determined. Furthermore, GRACE continuously since May 2006, precise information on global temperature and water vapor distributions ready. These are calculated using the innovative GPS Radiookkultationsmethode for Atmospheric Remote Sensing in analogy to the CHAMP measurements.

The two satellites were designed for a lifetime of five years. After over ten years in orbit, however aging of the components, the satellite can not record more data, for example, on the night side of the earth because can provide enough energy without sunlight the batteries to not. A follow-up mission is planned. The production of the two satellites, which in August 2017Vorlage: / should start tomorrow in 3 years, takes place at Astrium.