On Wednesday, the 235-foot Delta IV Heavy rocket will lift off from the base's Space Launch Complex 6, leaving a thick white plume over the Pacific.
The rocket, the tallest ever to be launched from the base, is set to place a classified spacecraft into polar orbit for the National Reconnaissance Office, the covert umbrella agency that operates spy satellites. Air Force security and local police have closed nearby locations as a precaution.
Although little is publicly known about what exactly the rocket will be carrying into space, analysts say it is probably a high-powered spy satellite capable of snapping pictures detailed enough to distinguish the make and model of an automobile hundreds of miles below.
This is the second time that a Delta IV Heavy will be launched from Vandenberg. The first time, in January 2011, a sound wave as loud as a freight train swept over nearby Lompoc, a town of about 43,000.
Some people reported hearing the rocket's roar as far away as 50 miles. Vehicles were stopping on the southbound shoulder of U.S. 101 to watch it hurtle into the afternoon sky.
The rocket was built by United Launch Alliance, a joint venture of Lockheed Martin Corp. and Boeing Co. It made its maiden flight in 2004 and is capable of lifting payloads of up to 24 tons into low Earth orbit.
Three hydrogen-fueled engines - each roughly the size of a pickup truck - will guzzle nearly a ton of propellants per second to provide 17 million horsepower. When the engines do roar to life, more than 200 Aerojet-Rocketdyne engineers and technicians will be watching.
It took the company five years to develop the engines at the company's sprawling Canoga Park, Calif., facility during the 1990s. It was also where the engine parts were fabricated before being assembled in Mississippi.
Wednesday's mission, designated NROL-65, has stayed on schedule for months.
Although Cape Canaveral, Fla., is the launch site for NASA's civilian space program, Vandenberg has been the site of military space projects for more than half a century.
Vandenberg, a 98,000-acre base along the Pacific, has been the primary site for launching spy satellites since the beginning of the Cold War because of its ideal location for putting satellites into a north-to-south orbit.
Space Launch Complex 6 is known on base as "Slick Six." The launch pad was built in the 1960s and later was intended to accommodate space shuttle launches, but they remained in Florida. Since then, the pad has gone through many renovations. Most recently, Vandenberg spent $100 million on upgrades over three years.
The launch is slated to be webcast Wednesday at rocket maker United Launch Alliance's website at http:/// www.ulalaunch.com.
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