The Delta IV Heavy rocket is scheduled to lift off from Vandenberg Air Force Base at 1752 GMT, according to United Launch Alliance.
The rocket is set to send a classified spacecraft into orbit for the NRO, which is in charge of U.S. intelligence-gathering satellites.
It's the second time that a Delta IV Heavy rocket will be launched from Vandenberg. In January 2011, a sound wave as loud as a freight train swept over a nearby town. Some people reported hearing the rocket's roar as far as 50 miles (80 kilometres) away.
United Launch Alliance is a joint venture of Lockheed Martin Corp. and The Boeing Co. to provide space launch services to the U.S. government with their Atlas and Delta rocket programs.