An unmanned rocket turned night into day early Thursday as two heavily armored NASA spacecraft were launched into orbit to study Earth's harsh radiation belts, after a week of delays.

The twin Radiation Belt Storm Probes launched at 4:05 a.m. ET from Florida's Cape Canaveral Air Force Station, soaring into space atop an unmanned United Launch Alliance Atlas 5 rocket. The liftoff had been planned for Aug. 23, but it was pushed back two days due to technical glitches, and then another five days to avoid foul weather from Tropical Storm Isaac.

"It was a wonderful event, a very smooth countdown," NASA launch manager Tim Dunn said after the launch, adding that the Atlas 5 gave NASA's newest science satellites "a great ride."

"We're all thrilled. Just excited as can be," Dunn added.

After a 60-day commissioning period on orbit, the radiation-tracking spacecraft will begin the science phase of their two-year mission, which aims to help scientists understand how Earth's two doughnut-shaped Van Allen radiation belts affect our planet's space weather.

Such information could have considerable practical applications, researchers said, since extreme space weather can knock out satellites and disrupt GPS signals, radio communications and power grids.

"RBSP will be able to predict the extremes and the dynamic conditions of space weather," Mona Kessel, program scientist for the $686 million mission at NASA Headquarters in Washington, told reporters during a prelaunch briefing on Aug. 20. [Launch Photos: NASA's Radiation Probes Blast Off]

Mysterious radiation belts The twin solar-powered probes will ply the Van Allen belts, where trillions of high-energy charged particles from the sun have been trapped by Earth's magnetic field. These fast-moving particles can damage satellites and potentially pose a threat to orbiting astronauts.

To deal with this harsh radiation environment, critical components on each RBSP spacecraft are shielded by 0.33 inches (8.5 millimeters) of aluminum.

The inner Van Allen belt usually extends from the top of Earth's atmosphere to about 4,000 miles up (6,437 kilometers), while the outer one runs from around 8,000 to more than 26,000 miles above our planet (12,874 to 41,842 kilometers). The belts are dynamic, however, and can expand greatly during solar storms.

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NASA launches probes to study radiation belts