It has been described by every worn cliche in the book, most notably the "Big Bang," but the demolition of two huge metal structures at Launch Complex 41 at Cape Canaveral Air Station will truly be "Out with the old, in with the new."

It should indeed be a "Big Bang" on Thursday at 10:00 a.m. ET when 275 pounds of explosives will knock down 7 million pounds of metal.

To be demolished are the Launch Complex 41 Umbilical Tower (UT) and the Launch Complex 41 Mobile Service Tower (MST), which is the largest moving vehicle in the world. Both have most recently been used to support launches of Air Force Titan IVB rockets, the largest and most powerful unmanned rockets in the United States.

The complex supported its first launch -- an Air Force Titan III-C rocket -- on December 21, 1965. The most recent launch was of an Air Force Titan IVB rocket on April 9, 1999. There have been 27 launches from Launch Complex 41.

"There are a few NASA folks who will have tears in their eyes Thursday, but we think this work will be extremely important to the U.S. launch industry in years to come," said Lockheed Martin Launch Site Manager Tim Meehan.

Indeed, Launch Complex 41 represents hallowed ground for NASA. The NASA Viking 1 and 2 Mars landers were launched from the complex in 1975, as were the NASA Voyager 1 and 2 deep space probes in 1977. These remain among the most popular missions in NASA history.

On the other hand, the Air Force would just as likely forget the facility. The two most recent launches from the complex were failures, the more dramatic of which was the explosion of an Air Force Titan IVA rocket 42 seconds after it was launched on August 12, 1998.

Now, the countdown clock is ticking, so to speak, toward the Launch Complex 41 demolition, now firmly set for Thursday, weather permitting. "When the button is pressed, the umbilical tower and mobile service tower should be felled like trees," said Glen Miller, Project Superintendent for Hensel Phelps Construction Company, which is refurbishing the complex.

But if they are trees, they will be big ones. The UT measures 200 feet tall by 50 feet wide by 75 feet deep and weighs 2 million pounds. It is a fixed structure, acting as a support for vital connections until the very second the rocket is launched.

Even more impressive is the MST, which measures 265 feet tall by 100 feet wide by 75 feet deep. It weighs 5 million pounds and acts as a support structure for pre-launch operations. A few hours before launch, the MST moves under its own power to a parking area about 500 feet from the launch pad. It is the largest moving vehicle in the world.

At least it will be until Thursday, when 275 pounds of explosives will knock the UT and MST down at the knees, causing the mammoth structures to fall onto special sand embankments created to lessen the shock of impact. The fall is expected to take about 30 seconds.

"The explosives are detonated by a push button, with all the explosives connected by just one wire," explained Tom Archer, Superintendent for Olshan Demolishing, the company hired to perform the demolition.

Although a symbolic countdown and button push will be carried out at a VIP site about 2,500 feet from the launch pad, the actual detonation will be controlled from a building located about 1,000 feet from the launch pad. "We could get a lot closer, but we decided to play it safe," added Archer.

Rumors that the demolition will be featured in the upcoming Clint Eastwood film "Space Cowboy" appear to be unfounded. "They are not involved in the demolition in any way," said Meehan.

But Lockheed Martin spokeswoman Joan Underwood exclaimed, "Of course, if they want to come and take pictures, we'll get them in."