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Nasa’s Jet Propulsion Laboratory (JPL) in California has selected France-based Astrium to develop two new research satellites, which will be used to measure the Earth’s gravity field.

The agreement was signed in Friedrichshafen, Germany. During their five-year mission beginning in 2017, the new Gravity Recovery and Climate Experiment Follow-On (Grace FO) units will measure data gathered by the first twin Grace satellites on Earth’s gravity field since their launch in March 2002.

Measuring approximately 3 x 2 x 0.8m and weighing 580kg, each Grace FO satellite will be positioned in a polar orbit, 500km above the Earth, and they will be positioned 220km apart.

The distance between the two new satellites will vary under the influence of the planet’s gravity, which will offer data for continued measurement of Earth’s gravitational field.

Measurements taken by the two research satellites are expected to be precise as their positions will be determined with the help of onboard GPS receivers, while a microwave link between the two will calculate the actual distance to within a few thousandths of a millimetre.

"Scientists can generate an updated model of the Earth’s gravitational field every month."

The distance will also be calculated using lasers, an experiment that can be used in future gravity-research satellites.

Using these values, scientists can generate an updated model of the Earth’s gravitational field every month.

Every day, these satellites are expected to create some 200 profiles of temperature distribution and water vapour content in the atmosphere and ionosphere.

With the help of the first two Grace satellites, geoscientists have been able to gain new understanding about the Earth’s interior, deep and surface currents in the oceans, and variations in the ice levels at the poles and over mountain ranges.

Astrium’s other scientific missions based on its satellite platform include Champ, GOCE and Swarm.


Image: An artistic rendering of Grace FO satellites, which will measure the data gathered by the first twin Grace satellites on Earth’s gravitational field. Photo: courtesy of Astrium.