The European Space Agency is launching the Cryosat-2 spacecraft into orbit to assess the state of ice cover at the Earth's poles.
It is being launched on top of a converted intercontinental ballistic missile from the Baikonur cosmodrome in Kazakhstan.
The launch is scheduled for 1357 GMT.
The information it gathers will help researchers calculate how melting polar ice affects ocean circulation patterns, sea level and global climate.
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