The Radiation Belt Storm Probes are in orbit after a successful launch atop a United Launch Alliance Atlas V rocket at 4:05 a.m. EDT from Cape Canaveral Air Force Station in Florida, the space agency said.
Two previous launches were postponed for technical reasons and for weather consideration at the launch site.
"I'm very happy to report that we have two happy spacecraft on orbit," said Rick Fitzgerald, RBSP project manager from the John Hopkins University Applied Physics Laboratory, which is managing the mission for NASA.
"Many thanks to ULA and Launch Services Program for getting us on orbit, giving us a great ride and injecting us in exactly the orbit that we wanted to be in."
The twin RBSP spacecraft will fly in separate orbits throughout the inner and outer Van Allen radiation belts that encircle the Earth to study the sun's influences on the behavior of the radiation belts, which in turn can impact life on Earth and endanger astronauts and spacecraft in orbit, NASA said.