Gravity Recovery And Climate Experiment

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GRACE
GRACE
Type: Research satellite
Country: United StatesUnited States United States / GermanyGermanyGermany 
Operator: National Aeronautics and Space AdministrationNASA NASA / DLRGerman Aerospace CenterDLR 
COSPAR-ID : 2002-012A / B
Mission dates
Begin: March 17, 2002
Starting place: Plesetsk Cosmodrome
Launcher: Rocot
Status: burned out - follow-on mission active
Orbit data
Rotation time : 94.5 min
Track height: 450-500 km
Orbit inclination : 89 °
Eccentricity : 0.0018185786

The twin satellite Gravity Recovery And Climate Experiment ( GRACE ) is a project for the precise determination of the earth's gravity field in a low orbit .

The GRACE satellites are the successor to the previous CHAMP mission , which was launched in 2000. They are based on the Flexbus concept developed by Astrium , which enables the satellites to be manufactured relatively cheaply and quickly.

mission

Model of the small satellite GRACE in 1:20 scale, GeoForschungsZentrum

The satellites were launched on March 17, 2002 with a Rokot rocket from the Plesetsk Cosmodrome (Northern Russia) into an almost polar and circular orbit with an inclination of 89 ° and an initial altitude of 500 km. The satellites work according to the SST principle ( Satellite-to-Satellite Tracking ) : They circle the earth on the same (more precisely: correlated) orbit at a distance of about 200 km and use microwaves to continuously measure the mutual distance. This allows irregularities in the gravity field to be analyzed with high precision, although the gravity anomalies at a height of a few hundred kilometers are significantly weaker than on the earth's surface.

For example, if the first satellite approaches a region with increased gravity, it will be accelerated slightly (compared to an undisturbed orbit ) and the distance between the two will increase. If the second satellite reaches this point and experiences the acceleration in turn, the distance between the two is reduced again in a typical manner. Because of this quasi mutual chasing, but never catching up, the satellites were nicknamed "Tom" and "Jerry" .

technology

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

The two satellites were designed for a lifespan of five years. After more than ten years in orbit, however, the components age. For example, the satellites on the night side of the earth can no longer record data because the batteries cannot provide enough energy without solar radiation.

Data

Three-dimensional model of the Potsdam potato (2017), GeoForschungsZentrum

The scientific evaluation takes place at the CSR (Center for Space Research) at the University of Texas and at the GeoForschungsZentrum Potsdam (GFZ). The visualization of the gravity field anomaly of the earth by the GFZ became known as "Potsdam Potato", whereby data from other satellites and terrestrial measurement data are also included. Since the anomalies are greatly exaggerated for didactic reasons compared to the globe or elliptical representation of the earth, this earth model with its dents and dents is reminiscent of a potato.

GRACE also makes it possible to determine changes in the geoid with high precision from the collected measurement data. As a result, new aspects of geodynamics and independent research methods for oceanography and possibly climate change come into the sights of the scientists. A comparison of the data with those of the GOCE gradiometric satellite launched in March 2009 is in progress.

The measurement data from GRACE showed that the Antarctic ice mass has decreased by approx. 150 km³ within 3 years, which corresponds to an increase in sea level of 0.4 mm per year. Changes in the amount of groundwater could also be determined. Furthermore, since May 2006, GRACE has continuously provided precise information about global temperature and water vapor distributions. These are the innovative GPS - Radiookkultationsmethode determined to atmosphere remote sensing in analogy to the CHAMP measurements.

Furthermore, the data is analyzed again by a cooperation between several institutes of the Gottfried Wilhelm Leibniz University of Hanover , the Laser Center Hanover , the GEO600 , the PTB Braunschweig and the Bremen ZARM with the aim of further developing the models and minimizing false signals.

Data collected by GRACE-FO since 2018 confirmed continued mass loss in Greenland as well as Antarctica.

GRACE-FO

Reflection prism ( Carl Zeiss Jena (2016)) for the GRACE-FO mission, GeoForschungsZentrum

A follow-up mission "GRACE Follow-On" (GRACE-FO) will measure the changes in distance between the satellites by laser interferometry in addition to the microwave measurement . The two satellites, which launched on May 22, 2018, were manufactured by Astrium . They should orbit the earth at a height of 500 km at a distance of 220 km from each other. Instrumental core is a measuring instrument in the microwave range K . At the same time, the GRACE-FO's laser interferometer is used to demonstrate the technology for eLISA . Cooperation partners in this project are the Albert Einstein Institute Hanover , which makes contributions to the laser interferometer, the Helmholtz Center Potsdam - German GeoForschungsZentrum , which evaluates the data obtained, and NASA, whose Jet Propulsion Laboratory has coordinating tasks and the implementation of the Project at Goddard Space Flight Center . GRACE-FO is the only mission in space that can continuously observe mass transports in the Earth system.

See also

Web links

Commons : Gravity Recovery And Climate Experiment  - Collection of images, videos and audio files

Footnotes

  1. ↑ Stuart Clark: Spacewatch: twin research satellites head for burn-out , The Guardian, September 28, 2017, accessed March 13, 2018
  2. ↑ Stephen Clark: NASA procures satellites for new gravity mission. Spaceflight Now, December 2, 2012, accessed December 3, 2012 .
  3. ↑ Homepage
  4. ^ The institute of geodesy in the cluster of excellence QUEST
  5. ↑ Ice Sheets
  6. ↑ SpaceX's tweet confirming successful deployment of the GRACE-FO satellites ( Memento from May 22, 2018 in the Internet Archive )
  7. ↑ Astrium is building two new research satellites for NASA ( Memento from May 23, 2018 in the Internet Archive )
  8. ^ Grace Follow-On
  9. ↑ Gravity Recovery and Climate Experiment-Follow-On (GRACE-FO) Mission
  10. ^ First GRACE Follow-On Satellite Completes Construction
  11. ↑ Marie Heidenreich: Satellites measure the world water balance , bundesregierung.de from July 9, 2018, accessed on August 15, 2018