An unmanned Atlas 5 rocket lifted off on Thursday from Cape Canaveral Air Force Station in Florida, placing a pair of heavily shielded NASA science satellites into position to study Earth’s radiation belts.

The 190-foot (58-meter) tall rocket, built by United Launch Alliance, blasted off at 4:05 a.m. EDT (0805 GMT), soaring out over the Atlantic Ocean toward an orbit as far as 19,042 miles (30,645 km) above the planet’s surface.

Riding atop the rocket were the identical twin Radiation Belt Storm Probes, which are expected to spend two years surveying the Van Allen radiation belts, hostile regions that surround Earth and that most other spacecraft try to avoid.

“They’re now at home in the Van Allen belts, where they belong,” deputy project scientist Nicola Fox told reporters after the launch. “For the science team, the real work now begins.”

Named after University of Iowa physicist James Van Allen, the two doughnut-shaped belts of trapped particles were discovered in 1958 by Explorer 1, the first U.S. science satellite. They are held in place by Earth’s magnetic field, which traps the electrically charged particles from the sun and deep space.

How the belts form and why they sometimes balloon out is a long-standing mystery.

Understanding the phenomenon is more than scientific curiosity. Every spacecraft orbiting Earth, including the $100 billion International Space Station and its crew, fly through the high-radiation regions, which can degrade solar panels and affect electronics.

“Modern society depends on satellites and other space-based technologies ... making the research and understanding that will come from (the probes) invaluable to building better protected satellites in the future,” New Jersey Institute of Technology physicist Lou Lanzerotti said at a pre-launch news conference.

The satellites are expected to spend the coming two years flying in tandem through the heart of the radiation belts. The inner belt begins about 650 miles (1,046 km) above Earth and extends to about 8,000 miles (12,875 km), but at times it can dip as low as about 125 miles (201 km). The space station flies about 250 miles (402 km) above the planet.