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.
Aside from answering some basic questions about physics, the $686-million Radiation Belt Storm Probes mission is expected to help engineers design satellites that can better withstand the harsh radiation environment surrounding Earth.
"Modern society depends on satellites and other space-based technologies that must operate in the belt, 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 told reporters during a prelaunch press conference.
Once in orbit, the satellites are expected to fly in tandem through the heart of the radiation belts. The inner belt begins about 650 miles above Earth and extends to about 8,000 miles, although sometimes it dips as low as 125 miles - well within the region where the International Space Station flies.
The outer belt begins at an altitude of about 8,000 miles and extends to about 26,000 miles, encompassing an area where communications and GPS satellites operate.
Scientists say two spacecraft are key to getting accurate measurements of how solar activity and other phenomenon impact the radiation belts.
HOWSTUFFWORKS: Van Allen Radiation Belts
"If you imagine sitting on a life raft in the ocean and you suddenly go down and come up again, you don't know very much about what caused you to go down and come up," said deputy project scientist Nicola Fox.
"If you have a friend who is sitting on a life raft a little way away, you can say ‘Well, did we both go down and up at the same time?' In which case it's a big-scale feature like a tsunami. Did one of us go down and then the other one? You can really start to look at the global dynamics of what's happening in the radiation belts," Fox said.
Image: Artist's rendering of the Van Allen radiation belts, two giant rings of charged particles that circle Earth. Credit: NASA/T. Benesch, J. Carns