An Atlas 5 rocket blasted off from Cape Canaveral Air Force Station in Florida before dawn on Thursday, carrying a pair of science satellites that will make the first detailed studies of Earth's Van Allen radiation belts.
After waiting out delays for a technical problem and stormy weather associated with Tropical Storm Isaac, the 190-foot tall rocket lifted off from its seaside launch pad at 4:05 a.m. EDT.
Riding on top of the booster are NASA's Radiation Belt Storm Probes, identical twin, radiation-hardened and heavily shielded satellites designed to spend the next two years studying a hazardous region around Earth that most other spacecraft try to avoid.
The so-called Van Allen radiation belts, named after University of Iowa physicist James Van Allen, have remained largely a mystery since their discovery in 1958 by NASA's first science satellite, Explorer 1.
The two doughnut-shaped rings of charged particles are held in place by the planet's magnetic field, but how they form and why they change shape is not well understood.