A Boeing Delta II rocket carrying the CloudSat and CALIPSO satellites blasted off at 1002 GMT Friday from Vandenberg Air Force Base in California.

The launch was carried live on NASA's satellite television channel.

Launches have been scrubbed daily for the past seven days due to weather or technical problems.

NASA was limited in part because the mission had a narrow one-minute launch window.

"There is not much margin to get (the satellites) in the exact orbit we want it to be," said NASA spokesman Bruce Buckingham. "It's an instantaneous launch window -- either you go or don't go."

A space shuttle flight usually has a 10-minute launch window, while other missions have launch windows of several hours, he said.

The satellites are designed to help answer questions about how clouds spread and deliver precipitation around the globe, as well as how they affect Earth's atmosphere and global warming.

Problems have plagued attempts to deploy the satellites since late last week. Last Friday's launch was scrubbed due to a communications malfunction, while the takeoffs planned for Saturday, Sunday and Monday were postponed because of problems with the refueling aircraft.

After they reached a 438-mile (705-kilometer) circular orbit -- 15 minutes after launch for Calipso and 30 minutes after that for CloudSat -- the new spacecraft were to fly in formation with the so-called "A-Train," a constellation with three other Earth observatories belonging to the US National Aeronautics and Space Administration and France.

The "A-Train" includes NASA's Aqua and Aura satellites and France's PARASOL.

The arrival of CloudSat and CALIPSO, scientists said, will help researchers gain new insights into the global distribution and evolution of clouds.

CALIPSO was developed in collaboration between NASA and France's National Center for Space Studies. It was shipped from the Alcatel Space facility in Cannes, France, to the United States last May.

The two satellites were initially scheduled to be launched last year, but technical problems and a strike at Boeing got in the way.

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