Visiting America's Rocket Factory

On several occasions over the last ten years I’ve had the pleasure of visiting the United Launch Alliance (ULA) rocket construction facility in Decatur, Alabama. This marvelous factory was first built by Boeing exclusively to build the Delta 4 family of rockets, but as time progressed, it later included the construction of Delta 2 rockets and now Atlas 5 rockets as well.

This factory LITERALLY takes in sheets of stock aluminum-6061 at one end of the factory and at the other end a finished Delta 4 rocket emerges. The steps in between were the subject of our tour.

First the sheet aluminum is milled by huge milling machines built by Cincinnati Milacron to create an “isogrid” pattern in the aluminum sheet. This process removes most of the material that was originally present in order to lighten the aluminum sheet while still preserving its strength. For the reason, the Decatur factory produces a vast amount of aluminum to be recycled–in fact, most of the aluminum that enters the facility will end up as aluminum chips.

Then the milled isogrid aluminum panels are bent on a huge machine into an arc 72 degrees in extent. The arced panels are rotated to a vertical position and five of them are positioned in a friction-stir welding machine that “zips” them together through the magic of friction-stir welding into a cylindrical barrel. Each core stage of the Delta 4 rocket has a liquid oxygen tank and a liquid hydrogen tank. The oxygen tank uses one barrel section, the hydrogen tank uses two. A different welding process joins two barrels (for the hydrogen tank) and then adds the single-piece caps to the tanks.

The LOX tank is pressure-tested using water (fairly safe) but the hydrogen tank is pressure-tested using compressed gas (not so safe). This is because water weighs about the same as LOX, but liquid hydrogen weighs so little that there isn’t a fluid that’s a good match, so they simply use gas. Pressure-testing the hydrogen tank is done in a chamber designed to contain the “explosion” if the tank fails. It’s pretty beefy–would make a good tornado shelter.

Then the tanks have spray-on foam applied, cured, and trimmed to create a smooth surface. In the final part of the factory, the LOX tank and hydrogen tank are joined by a composite intertank structure, then another composite thrust structure is added at the aft end of the hydrogen tank and the RS-68 engine is installed. The composite interstage structure is added at the top of the LOX tank if the core is the central or only core in the stack, or if the core is one of the two outerboard cores on the Delta 4 Heavy rocket, a composite “nose cone” structure is added.

The completed core then are sent out of the plant and down the road on a large trailer to the nearby Tennessee River, where they are loaded on a special boat called the Delta Mariner and carried down the river to the Gulf of Mexico. Then they either go around Florida to Cape Canaveral or through the Panama Canal to Vandenberg Air Force Base in California.

From stock aluminum to rocket, all in one building.

Now what does all this have to do with thorium and LFTR? Because I think the production of the Delta 4 rocket in Decatur is analogous to what we will need to do in order to build the hundreds, even thousands of liquid-fluoride reactors needed to power the world safely with thorium. It is not hard for me to envision a future factory where the raw materials for a finished LFTR arrive at one end of the factory: Hastelloy-N, hydrogen fluoride, raw lithium salts, beryllium, purified thorium, graphite prisms, nickel-based piping, heat exchange material, turbine and compressor blades and stator, and electrical generator assemblies.

The Hastelloy would be shaped and bent and welded into the reactor vessel, drain tanks, and another fabrication operation would build the primary containment. Into the primary containment would go the drain tanks first, and then the reactor vessel. Crews would attach and weld the freeze plug system to connect the tanks. The drain tanks would also be piped to external fill and drain systems.

Then the core inlets and outlets would be welded to the reactor vessel, used to connect the reactor to the primary heat exchanger, which would be constructed in another part of the factory. Side piping that would take core and blanket fluids to the integrated reprocessing system would also be added.

In another part of the factory, the gas turbines would be coming together. On a balanced shaft in a large forging would be placed the rotors and stators of the compressor and turbines. The finished casings would have gas inlets and outlets welded to both compressors and turbines.

Finally, the reactor system and the gas turbines would be connected to one another. Gas inlets and outlets would join the reactor system (with the primary heat exchange loop and the gas heaters) to the gas turbines. The entire system would be taken from the factory down to the river or seashore and the completed unit would be lowered into the water, to be towed to the next coal plant to be converted to clean thorium en
ergy.

With a factory analogous to the Delta 4 plant, I could envision a 400-MWe class LFTR rolling out the door every few weeks. With a production rate of 25 400-MWe cores per year, each factory could be producing 10 gigawatts of clean, baseload energy per year, and that would be a future worth working towards.