Rocket power

The rocket launch towers at Launch Complex 17 in Cape Canaveral, Florida, have withstood hundreds of high-impact blasts. Over a span of more than five decades, the towers stood firm as hundreds of rockets and other aircraft launched into space from their steel beams, leaving nothing behind but a trail of sparks.

With one last explosion in July, the two towers finally toppled to their fate in a cloud of smoke.

Demolition crews recently took out the two fixed launch towers on pads 17A and 17B at the Cape Canaveral Air Force Station to clear way for commercial operator Moon Express to launch moon-bound expeditions in the future. Located near the southern perimeter of the sprawling Air Force station, Complex 17 was one of the Florida spaceport’s oldest launch pads from which 325 missiles, satellites and rockets launched between 1957 and 2011.

Ames 1 LLC of Anchorage, Alaska, subcontracted D.H. Griffin Wrecking Company Inc. (DHGW), Greensboro, North Carolina, for the demolition work, which included the two towers, one of the launch pads, multiple ancillary support structures and all associated footings and foundations within the complex.

DHGW spent four months developing an initial plan to mechanically fell the structure.

Once contractors began pre-cutting steel structures, though, they discovered they’d need a new plan.

“As we started exposing columns and preparing for the precuts, we discovered that the degree of corrosion on and within structural members was too great to guarantee the necessary structural integrity required to safely proceed with this method,” says Karen Soricelli, a division manager at DHGW who helped oversee the project. “We made the decision to consult with Dykon Explosive Demolition Corp. (Tulsa, Oklahoma) and asked our client to appeal to the Air Force to allow for the utilization of explosive means in felling the towers.”

Plan B

Demolishing steel structures by means of explosion on a military base in the middle of Florida is no easy feat. Once explosives entered the picture, the Air Force implemented an additional set of stringent safety guidelines for carrying out the demolition—including a 99-pound cap on the amount of explosives that Dykon could use.

Successfully working within the limitations required almost an entire extra year of extensive planning coordinated between the three contractors and the Air Force. DHGW also hired two outside engineering firms to perform structural analysis and stamp the plan, along with another outside contractor to perform continuous monitoring throughout the prep work.

“Working on a military base always entails a heightened level of security. The process for approval regarding the change in method and use of explosives was lengthy due to the number of departments within the Air Force that had to review the plan,” Soricelli says.

The complex’s southern location presented an additional challenge, Soricelli adds, as the area was prone to seasonal thunder and lightning storms, and even hurricanes, that could delay work.

To develop the explosive plan, Jim Redyke, the president of Dykon, says he and his team walked the site and measured every particular, down to the individual columns, to help determine the quantity of explosives needed to fell the 190-foot towers.

While the site was relatively empty, the Air Force outlined which direction it wanted each structure to fall for cleanup purposes—Redyke just needed to figure out how to do it with limited impact.

“I think preplanning and engineering requirements are probably the most important things that are needed for a good blast. Owners always want to see exactly how you’re going to do it, so the more detail you give them going in, the more of a comfort level they can have,” Redyke says. “That’s part of good planning in any type of job: attention to detail and checking to make sure you have everything you need to know about the structure so you can plan accordingly.”

Minimizing the impact

After months of preparation and planning, the Air Force approved Redyke’s plan to use 97 pounds of explosives—just two pounds shy of the maximum allowed on-site.

Dykon was able to limit its use of explosives by torching the structure to pre-weaken it before the blast. The towers’ sturdy steel cross-brace composition, especially at the base of the structures, posed a challenge for contractors, who needed to eliminate some density at the base to create frame consistency all the way through the structure for easier control.

“The real secret is the art in the torch work you do,” says Ron Gilbert, the vice president of operations for Dykon. “Pre-weakening the structure with a cutting torch mitigates the amount of explosives you need.”

After abating asbestos and polychlorinated biphenyls (PCBs), demolishing the concrete launch pads and removing several ancillary structures on the site, contractors got to work methodically slicing through select intersections of steel beams, cutting slots into the columns that would help the towers topple in the right direction.

Once the structure was weakened, Protec Documentation Services Inc. of Hainesport, New Jersey, performed surveys of all structures on-site that were to remain to help assess any damage claims following the blast.

Prepare for blast-off

Before the detonation, the Dykon team placed 900 grains per foot of linear shaped charges in the towers to sever structural members, along with nitroglycerin-based dynamite to displace them. Explosives were placed about 43 feet high, leaving some of the tower intact near the bottom for the structure to pivot on to help direct its fall.

“If you can leave up a portion of the building as blast protection and tear it down later, that is important,” Redyke says.

The exact placement of explosives and sequencing of detonation, though, are details contractors keep close to maintain a competitive edge. “Every blaster is like a chef in the kitchen. Everyone cooks different, so you don’t want to let all your secrets out,” Gilbert says. “It’s cookie-cutter in a lot of respects, but you’ve got your own touches that you put in the food.”

Prior to the demolition, contractors designated impact areas and set up a safety perimeter. The Air Force required all spectators and personnel to remain at least 2,000 feet away from the towers, so Redyke spent nearly an hour routing a detonating cord to the designated site to use with both non-electric and electric detonators.

Protec was on-site the morning of July 18 to conduct seismic monitoring of the vibrations produced by the explosion, along with dozens of onlookers to say their final goodbyes to the historic towers.

The launch complex was built in 1956 to test the first operational ballistic missile in the U.S. arsenal. Over the years, its ownership was passed between the Air Force and NASA, making it a starting point for dozens of notable missions, including the Mars Exploration Rovers, Spirit and Opportunity.

With so much history, it was only right that a familiar face administer the towers’ final blast. After a warning siren, a countdown and a call to “fire in the hole,” Brig. Gen. Wayne Monteith, commander of the Air Force’s 45th Space Wing, pushed the detonator’s plunger.

Five loud pops sent the cereal box-shaped towers tipping in opposite directions: one fell toward the south, while its attached mobile tower and the other fixed tower fell to the north. Within 10 seconds, the towers were steel ruins on the ground.

Cleanup

Following the blast, DHGW mechanically demolished the remaining lower portion of the towers using hydraulic shears and took out the rest of the concrete foundation. Crews recovered approximately 1,400 gross tons of steel and more than 10,000 tons of concrete, Soricelli says—a majority of which was recycled, along with some asphalt and nonferrous metals.

Now that the towers were successfully demolished, a new generation of space explorers are moving in—all thanks to the careful collaboration among contractors who worked to clear the site to plot a new course of history.

“I always want to make sure the world knows these are joint efforts,” Redyke says. “Playing the team role here is really important.”

The author is assistant editor for Construction & Demolition Recycling and can be contacted at tcottom@gie.net.