Vandenberg Air Force Base officials say the Taurus XL rocket carrying NASA's Glory satellite lifted off about 2:10 a.m. PST Friday from the base.
But Nasa launch commentator George Dillar said 15 minutes later that a payload faring didn't separate from the Glory spacecraft and consequently it doesn't have the velocity to reach orbit.
He says says Launch Director Omar Baez has called for a contingency plan for the spacecraft. The status of the flight wasn't immediately clear.
Nasa officials declined comment when reached by The Associated Press, saying a press statement would be forthcoming.
Glory was launched on a three-year mission to analyze how airborne particles affect Earth's climate. Besides monitoring particles in the atmosphere, it will also track solar radiation to determine the sun's effect on climate change.
The $424 million mission is managed by the NASA's Goddard Space Flight Center in Maryland.