Swarm mission to map Earth's magnetism
22 November 2013 Last updated at 15:00 GMT
The Swarm mission to map the Earth's global magnetic field in unprecedented detail has launched from Russia.
The trio of European Space Agency (Esa) satellites left the Plesetsk Cosmodrome at 12:02 GMT, riding a Rockot vehicle.
They were deployed at an altitude of 490km, in a polar orbit, shortly after 13:30 GMT.
Swarm's data should help scientists understand better how the field is generated, and why it appears to be weakening.