The mobile service tower at Space Launch Complex-3 West is toppled on Saturday. Photo: U.S. Air Force

With a loud pop and puff of black smoke, a 35-year old launch tower came crashing down Saturday at Vandenberg Air Force Base in California.

The 140-foot tall cocoon-like mobile gantry that once served to shield Atlas and Thor rockets before liftoff at Space Launch Complex-3 West was toppled in a $100,000 demolition effort undertaken by Lockheed Martin.

The U.S. aerospace giant will spend the next three weeks dismantling and hauling away the tower's remains.

The pad was activated in 1960 and saw its first launch in October of that year.

In all, 81 rockets departed from the site that is nestled between mountains and the Pacific Ocean.

Nine Atlas D rockets with Agena upper stages were launched during the pad's first three years of life. From 1963 to 1972, 38 Thor-Agena rockets used the site. Following a period of modifications, the pad served 34 Atlas E and F boosters from 1974 to 1995. The last launch, an Atlas E with a U.S. military weather satellite, occurred on March 24, 1995.

An old Atlas rocket lifts off from Space Launch Complex-3 West. Photo: U.S. Air Force

Saturday's explosive event, the second in three months for Lockheed Martin, was done in the name of safety because the A-frame tower was weakened and posed a hazard.

Experts rigged about 20 pounds of explosives to the tower's front support legs. When the charges fired at about 2300 GMT (6 p.m. EST), the legs were blown out and the purposely-weakened back legs collapsed to allow the tower to topple over.

Workers last fall stripped the 400-ton tower of siding, wiring, cables and its hydraulic equipment to prepare for demolition.

Officials opted to bring the tower down instead of dismantling it piece by piece while standing upright. That would have been more costly and taken months, not to mention it could have proved deadly for workers riding cranes.

The demolition was slated for October, but officials delayed the operation so the company could focus on the remodeling effort underway at Florida's Cape Canaveral Complex 41. That East Coast pad was demolished in similar fashion on October 14.

Both Complex 41 and SLC-3 West were picked to serve as the launch pads for Lockheed Martin's next generation Atlas 5 rocket family. The boosters will use streamlined pre-launch processes than do not need the mobile service towers of old.

Artist's concept of an Atlas 5 rocket sitting on the new Complex 41 at Cape Canaveral. The assembly building is seen in background. Photo: Lockheed Martin

Instead of being assembled at the pad, the rockets will be put together in nearby buildings and rolled to the pad a day before liftoff.

Construction is well underway in Florida for the new pad set to hold its inaugural launch late next year, but plans at Vandenberg remain tentative.

"There is no rush to build anything at that site right now," Lockheed Martin spokeswoman Joan Underwood said.

The nearby SLC-3 East pad was rebuilt a few years ago for the Atlas 2 series of rocket and saw its first launch in December.

Officials might opt to fly Atlas 5 rockets from a retrofitted SLC-3 East instead of using SLC-3 West.

The company is investing more than $1.5 billion to develop the Atlas 5 fleet in conjunction with the U.S. Air Force's Evolved Expendable Launch Vehicle program.