SpaceX launched two US-German research satellites into Earth orbit on Tuesday as part of a collaborative initiative to monitor changes in the earth's mass to better predict the effects of droughts.

The car-sized satellites were deployed minutes after taking off aboard a Falcon 9 rocket from Vandenberg Air Force Base in California.

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The German Center for Geosciences (GFZ) and the US National Aeronautics and Space Administration (NASA) are set to use the payload as part of their Gravity Recovery and Climate Experiment-Follow On (GRACE-FO) mission.

The satellites will orbit the earth once every 90 minutes at an altitude of 304 miles (490 kilometers) at a set distance of 137 miles apart. The initiative builds on GRACE, which examined changes in the Earth's water and its mass by measuring tiny variations in the planet's gravity.

Building on 'Revolutionary mission'

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"GRACE was really a revolutionary mission for us understanding the water cycle and how the climate behaves and the trends which are taking place over the last 10 or 15 years," said Frank Webb, a GRACE-FO project scientist.

GFZ contributed €77 million ($91 million) to the project, while NASA contributed $430 million. European aerospace giant Airbus built the identical satellites in the southern German town of Friedrichshafen.

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SpaceX also launched five communications satellites for US-based Iridium Communications from the same Falcon 9 rocket during the spacecraft's second stage. The company is planning to spend $3 billion to replace its entire fleet of commercial communication satellites.

After a launch in January, the Falcon 9's first stage was recovered, but SpaceX did not repeat the feat with Tuesday's launch.

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amp/rc (AP, AFP, dpa)