By Irene Klotz
CAPE CANAVERAL, Florida (Reuters) - An unmanned Atlas 5 rocket lifted off from Cape Canaveral Air Force Station in Florida on Thursday to put a classified satellite into orbit for the U.S. National Reconnaissance Office.
The 20-story tall rocket, built by United Launch Alliance, blasted off its seaside launch pad at 1:45 p.m. ET (1745 GMT). United Launch Alliance is a partnership of Lockheed Martin and Boeing.
No information about the rocket's payload was released. The secretive National Reconnaissance Office designs, builds and operates the nation's fleet of spy satellites.
The rocket was outfitted with a single upper-stage Centaur engine and four strap-on solid rocket motors, all built by Aerojet Rocketdyne. In that configuration, the Atlas 5 can deliver up to about 7,800 pounds (3,500 kg) into an orbit 22,300 miles above Earth, United Launch Alliance documents show.
Launch originally was slated for March 25, but a radar system needed to track the rocket during flight short-circuited, prompting a delay. The Air Force reactivated a spare radar while repairs to the damaged system are under way.
The radar is part of a safety system that ensures a failed rocket will not threatened populated areas. If a rocket leaves its planned flight path, officials can detonate explosives on the vehicle so that debris rains down in the ocean.
The radar problem also sidelined a Space Exploration Technologies' Falcon 9 rocket launch for NASA that had been scheduled for March 30. The rocket, now targeted to fly on Monday, will be carrying a Dragon cargo capsule to the International Space Station, a $100 billion research laboratory that flies about 250 miles above Earth.
(Editing by James Dalgleish)