Mon February 11, 2013
A Look at Tethered Aerostats
A private company in Elizabeth City is manufacturing a lighter than air technology called a tethered aerostat. They're being sold to governments and are the worlds only company devoted entirely to the production of these unique products. We recently toured the massive facility.
From the road, Weeksville air station is unassuming. But if you get up close, the sheer size and breadth of the facility is overwhelming. The largest structure on the complex is the hangar, which is nearly 1,000 feet long and 300 feet wide. It was used to store blimps during World War II. Now, the site is being used to manufacture what is called an aerostat. An aerostat is a large, inflated balloon which is tethered to the ground and outfitted with surveillance equipment. TCOM's Safety and Training Coordinator and Historian, Stephen Chalker.
"There's a chain of them on the southern border of the United States watching for drug smugglers. The larger sized ones are typically equipped with a radar on the belly of them, so from a altitude of 10000 feet above ground level they can see out in all directions and are not affected by the curvature of the earth. Our smaller ones have been used in Iraq and are being used in Afghanistan for base security, they put them up with day and night cameras and watch for infiltrators."
On land, they're used for security at military bases. In the air they'll detect low flying aircraft and/or missiles. Or on the water, they're tied to the back of a battleship or carrier. The balloons optical sensors, thermal imaging and night vision technology polices the waters, staving off piracy and smuggling, or in less threat based situations will provide service to search and rescue teams, or will be used to watch over fishing activity.
TCOM was started as a subsidiary of the Electric giant Westinghouse. Their clients have almost exclusively remained governments. In their early years, tethered aerostats were built for communications purposes, used in developing countries, and remote areas around the world.
The process of designing the aerostat material takes place on a long table, a mix of a conveyer belt, and air hockey table. A special material designed by TCOM is bonded to a material similar to sailcloth.
"So the first thing that happens is the material is written on, the material is lying inside or backside up. So what gets written on there comes out basically looking like a dress pattern, you have match marks so everything is lined up and it shows you where everything goes. The next pass will be the cutting pass, so the parts are cut, we put them on these racks over here and the floor supervisor will assign a person or a team of people to start the assembly."
The assembly team uses thermal bonding, where heat and pressure bind the layers together. Next, the aerostats are tested in dock 1, in the hangar that rises nearly 200 feet off the ground.
It's the only steel hangar left of the two built before WWII for squadrons of blimps. In the 40's and 50's blimps were stored and serviced in two hangers in Elizabeth City, one made of steel, the other made of wood. At the time, it was the world's largest wooden structure. The airships, or dirigibles, patrolled the Atlantic Ocean and led convoys, spotting submarines with great success. They predominately patrolled off the coast of the Outer Banks. Before the blimps were used, at least one ship was lost every day off the North Carolina coast. When the blimps went into service, that number dropped significantly to one every two and a half months. After World War II, the hangar was no longer used for blimps. Instead, it stored planes, vehicles, and even kitchen appliances. At one point, it was the testing site for the first satellite to be launched in space, a metallic balloon that's reflective surface was used to bounce radio waves off of.
TCOM was started in 1971, and the wooden hangar was purchased.
"Our biggest defining moment was August 3rd 1995 when we discovered that the world's largest wooden building also makes the world's largest bonfire. Having lost everything in that facility, all our production equipment, all our raw materials, completed Aerostats, and some blimps that happened to be in the hanger at that time, we were back in business in 45 days. We took up residence in a vacant Kmart in town and were able to complete all our contracts for that year."
About a year after the fire they bought Dock 1, the steel hangar. Now, the space is used for what they call the checkout process. First aerostats are inflated to .127 psi. an initial inspection is done, and then a tedious process called "pinholing."
"Someone will be on the inside and someone will be on the outside with that big lamp and they go over the entire thing with the person on the inside watching for pinholes of light to come through the material and when they see one they patch it."
To keep aerostats from popping they use a ballonet, which is basically a smaller balloon within the bigger one.
"On the ground that ballonet is filled with air. As the aerostat or the blimp goes up and the helium in the rest of it expands it pushes the air out of that ballonet through valves."
The air in the ballonet maintains the ships buoyancy by regulating the amount of pressure in the balloon, but more importantly, it keeps the helium molecules inside cool enough so they don't expand.
After pinholing, the aerostat goes through a stress test, then repeat inspections, and finally they are tested with helium. Chalker shows us one of the aerostats being helium tested.
"This particular one is obviously used. this one has come back from Iraq and sent to us to evaluate and tell the government is it worth preparing, is it not, it's easy to tell which one's have come back, well when they left here they were white, and now they're sort of sand colored. Now, I'll answer a question that always gets asked okay what if someone shoots at these?"
.127 psi is a very low pressure, so low, that if the aerostat is pierced it won't burst. It will slowly leak.
While the team at TCOM's headquarters in Columbia Maryland, approve all the data from the helium float test, the site in Elizabeth City will often install the surveillance equipment. The payload, as they call it is usually installed underneath the balloon. In the process of building their aerostats TCOM has to work closely with both the customer, and surveillance developers.
They have to know where the Aerostat will be operated, how heavy the payload will be, and how high in altitude they want it.
"A good example would be Iraq and Afghanistan. In Iraq to carry the same equipment, they could use a 17 meter aerostat, in Afghanistan to carry that same equipment we had to go to a 22 meter aerostat because Afghanistan is like 5, 6 thousand feet above sea level, so in order to get to the same altitude off the ground we had to take that altitude off of sea level into consideration and size the aerostat accordingly."
Aerostats are kept in place with a mooring system that works like a fishing rod. The tether is the line, and the moor, which is either mobile or immobile, works like the rod. The tether itself is very strong, usually made of Kevlar. It has electrical conductors in it to power the aerostat and the mooring system, and it is also equipped with fiber optic cables, making it responsible for getting the data from the payload down to the crew on the ground.
I ask about the viability of an aircraft that doesn't have the advantages of the mobility of a drone or the stealth of a satellite in space. Chalker says the aerostats are cost effective, and are able to run for weeks at a time, which makes them, at least for now, indispensable.
Unfortunately, cameras were not allowed in the hangar, but an aerostat was grounded outside, and we get snapped a picture of it. You can see the aerostat at Publicradioeast.org.