Three Swarm satellites equipped to study the Earth's magnetic shield were vaulted into space Friday atop a Russian launcher and reached orbit less than two hours later, the European Space Agency said.

The Rokot launcher left the pad at the Plesetsk cosmodrome in northwestern Russia at 12:02 GMT.

A little more than 90 minutes later, the launcher's Breeze-KM upper stage released the satellites into a near-polar circular orbit at an altitude of 490 kilometers (305 miles).

The ESA's operations center here in Darmstadt quickly established contact with the satellites through ground stations in Sweden and Norway.

The next crucial phase begins at 21:00 GMT Friday, when the Swarm satellites begin the process of deploying the 4-meter (13-foot) booms carrying the sensors to be used in the mission.

The satellites will shift to their operational orbits over the next 90 days.

Once in place, two of the devices will travel side-by-side above the equator at an altitude of 460 kilometers, while the third is to orbit the Earth at a higher altitude, 530 kilometers.

"The Swarm satellites will give us unprecedented insights into the complex workings of the magnetic shield that protects our biosphere from charged particles and cosmic radiation," the ESA said in a statement.

ESA hopes the data collected by the satellites over the next four years will help explain a recently detected weakening in the magnetic shield. EFE