Video: massive Delta IV Heavy rocket launches US spy satellite

A massive rocket carrying a spy satellite for the US government has been launched from California.

The Delta IV Heavy rocket left the launch pad at Vandenberg Air Force Base on Wednesday and sped toward low-Earth orbit.

The rocket carried a satellite for the National Reconnaissance Office, which oversees the nation's constellation of intelligence-gathering satellites.

Since the mission is classified, no other details were available.

United Launch Alliance is a joint venture of Lockheed Martin Corp and Boeing to provide space launch services to the US government with their Atlas and Delta rocket programs.

At 23 stories, the Delta IV Heavy is the largest US rocket. The last time it launched from Vandenberg - in 2011 - the roar of the engines shook the nearby city of Lompoc. Some people reported hearing the engine roar from 50 miles away.

This time around, the three main engines were ignited one after another to lessen the impact during liftoff.