VANDENBERG AIR FORCE BASE, Calif. (AP) -- A rocket carrying a top-secret payload blasted off Tuesday from the California coast.

The Delta IV rocket lifted off at 4:12 p.m. From the Vandenberg Air Force Base, about 130 miles northwest of LA.

"We've just seen the successful liftoff" of the rocket, launch commentator Don Spencer claimed in a webcast.

Since the launch involved a classified cargo for the Nation's Reconnaissance Office, no details were instantly available about whether it was boosted to its intended orbit.

The reconnaissance office, which supervises the nation's constellation of spy satellites, has kept mum about the object of the mission and directed United Launch Alliance to chop off the live broadcast 3 minutes after liftoff.

Intelligence researchers believe the rocket carried a radar imaging satellite capable of seeing at night and through bad weather. In recent times, the U. S. has worked to phase out its fleet of older, heavier radar reconnaissance satellites with smaller but equally able ones, claimed Charles Vick, a space policy analyst with the Globalsecurity.org working party.

Such radar satellites would be well placed to zero in on countries of interest and see details that classic Earth satellites can't, specialists said.

Tuesday's launch involved reconfiguring the rocket to add on two strap-on boosters to provide more thrust. The protective nose cone enclosing the cargo also had to be made larger.

ULA, the partnership of rocket builders Lockheed Martin Co. And Boeing Co, expounded it was the first time the Delta IV had been launched this way.

The launch was delayed almost a week as engineers worked to fix an issue with the higher stage engine.

The next launch out of Vandenberg will be a flight test of the Minuteman III on April 10.

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