The $1.5 billion National Polar-orbiting Operational Environmental Satellite System Preparatory Project, or NPP, lifted off into the darkness at 5:48 a.m. from Vandenberg Air Force Base in California.
An United Launch Alliance Delta II rocket was carrying the satellite to orbit.
"Smooth ride," declared Flight Commentator Steve Agid.
The NPP spacecraft was scheduled to separate from the rocket's upper stage just under an hour into flight.
NASA and ULA teams from the Cape were in Vandenberg for the launch.