Rocket carrying Air Force satellite blasts into space

A Delta 4 rocket blasted off, carrying a U.S. national security satellite into space.

The 23-story rocket, which replaced the Titan fleet two years ago, blasted slowly at 8:50 p.m. Saturday, taking nearly 15 seconds to clear the launch pad.

The 1.6 million pound (730,000 kilogram) rocket, which can carry the military's largest payloads, uses three common booster cores that are strapped together with a trio of hydrogen-fueled motors and then added to an upper stage rocket.

It carried the 23rd and final satellite of the Air Force's Defense Support Program. The satellite was expected to set into orbit 6 1/2 hours after liftoff, more than 22,000 miles (35,000 kilometers) above the Earth.

The reconnaissance satellites use infrared sensors that detect heat from missile and booster plumes against the background of the Earth.