Three European Space Agency satellites designed to study Earth’s magnetic field were launched Friday aboard a Rokot carrier from a space center in northern Russia.

The ESA satellites, carried by the Russian-made launcher with a Briz-KM upper stage booster, blasted off at 4:02 p.m. Moscow time (1202 GMT) from the Plesetsk space center.

The three Swarm satellites will examine the magnetic field that protects the planet from cosmic radiation and charged particles carried by solar winds, making life possible on Earth.

Two satellites will initially fly at an orbital height of 460 kilometers (290 miles), which will be reduced over four years to 300 kilometers. The third will fly at 530 kilometers to offer a different angle.

The Swarm satellites are expected to reach their target orbit at 5:33 p.m. Moscow time (1333 GMT).

The launch had been scheduled for mid-2012, but was postponed several times following concerns about Briz booster malfunctions.

The Plesetsk Cosmodrome, located about 800 kilometers north of Moscow, is a military installation that acts an alternative launch pad for Russia to the Baikonur space center in Kazakhstan.