Tag Archives: friction stir welding

A (much) Closer Look at How We Build SLS

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By Martin Burkey

How do you put the world’s largest rocket under a microscope?

One piece at a time, of course.

NASA’s Space Launch System – SLS – will be the world’s most powerful, capable rocket. It will send intrepid explorers, their spacecraft, their landers, their habitats, and all their other equipment to survive and thrive in deep space.

But, first, it has to survive launch. SLS is an extreme machine for operating in extreme environments – 6 million pounds going from zero to around 17,500 miles per hour in just 8 minutes or so after liftoff. Some parts are minus 400 degrees F. Some parts are 5,000 degrees. Extreme.

So NASA works hard to make sure everything works as planned, including the largest part, the core stage – 212 feet long, 27 feet in diameter, and weighing more than 2 million pounds all gassed up and ready to go.

NASA and core stage prime contractor Boeing are building hardware at Michoud Assembly Facility in New Orleans, Louisiana for the first flight in 2018. Engineers have put the design through numerous computerized structural analyses and simulations, but that’s not the same as actually cutting, welding, and assembling giant metal panels, domes, rings, etc. on new manufacturing tools with new processes for the first time. Each time, the team starts to weld new flight hardware, they methodically go through a series of steps to make sure that first flight hardware is perfect.

SLS liquid oxygen tank weld confidence article comes off the Vertical Assembly Center at Michoud Assembly Facility.

A liquid oxygen tank confidence article for NASA’s new rocket, the Space Launch System, completes final welding on the Vertical Assembly Center at Michoud Assembly Facility in New Orleans.

“Perfect” is a relative term. Some technically-minded people consider welding itself as a defect in a metal structure because the weld is never as strong as the rest of the metal, according to Carolyn Russell, chief of the metal joining and processes branch at Marshall Space Flight Center in Huntsville, Alabama, with 32 years of experience in the field. Given the advanced state of welding technology, other people might consider the term “defect” as a bit extreme.

None other than legendary rocket scientist Wernher von Braun declared in the midst of Saturn V moon rocket development in 1966: “A lifetime of rocketry has convinced me that welding is one of the most critical aspects of this whole job.”

The first step to SLS flight hardware was establishing the “weld schedule,” – how the welding will be done. SLS uses “friction stir welding” – a super fast rotating pin whipping solid metal pieces until they are the consistency of butter and meld together to bond the core stage’s rings, domes, and barrel segments. The result is a stronger and more defect-free weld, than traditional methods of joining materials with welding torches.

The completed SLS Launch Vehicle Stage Adapter awaits testing.

The completed SLS Launch Vehicle Stage Adapter (LVSA) structural test article awaits transfer to a test stand at NASA’s Marshall Space Flight Center in Huntsville, Alabama. Measuring 56-feet tall, the LVSA connects the SLS core stage to the upper stage.

Based on the particular aluminum alloy and thickness, engineers establish the required pin rotational speed, travel speed, how hard it pushes on the metal Before committing the welding schedule to full size or flight hardware, the core stage team checks the process on test panels about 2 feet long. Test panels are made at Michoud and sent to Marshall, where they are nondestructively inspected, sectioned and then analyzed microscopically for minute defects.

A false color composite image of the metal grain in an LVSA panel.

A false color composite image produced by an electron beam microscope at NASA’s Marshall Space Flight Center shows the crystal orientation of a portion of the thickness of a metal panel for the Launch Vehicle Stage Adapter.

Marshall materials scientists study the samples under magnification in the search for cracks and voids, and to understand how deeply the weld penetrated the parts. They also undergo non-destructive evaluation, including x-ray, ultrasonic, and dye penetrant testing.

With weld processes tested for every part of the core stage, the manufacturing team can begin building weld confidence articles, or “WCAs.” There are WCAs for the engine section, the liquid oxygen tank, and the liquid hydrogen tank. Likewise, the WCAs are cut into samples that are again put under the microscope at Marshall. In theory, the WCAs should be perfect if the weld schedule was followed. In reality, it doesn’t quite work out.

WCA welding consists of lots of “firsts,” Russell explained. It’s a test of the tooling and factors like parts alignment and tolerances. Heat transfer from the welds to the surrounding metal is different once large parts are clamped together. It short, stuff happens. Adjustments are made. Weld samples are cut and again put under the microscope until the weld schedule is perfected.

All this testing and microscope-gazing has led to a major SLS milestone: the welding of structural test articles – STAs – and flight articles for the hydrogen and oxygen tanks, engine section, and forward skirt, which is underway now. The STAs will be shipped to Marshall next year. Secured into test stands – that are secured firmly to the ground – these test articles will be rigged with hundreds of sensors and then pushed and prodded to see if they can survive the stresses the flight hardware will experience – accelerating bending, twisting, etc.

Then, and only then, can engineers say that the giant core stage is ready for its launch debut. But that’s a story for another day.


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Small Hitchhikers Ride through the Galaxy

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By Beverly Perry

On the first launch of the Space Launch System (SLS), America’s next-generation heavy-lift rocket, the Orion Stage Adapter (OSA) will carry 13 CubeSats, or boot box-sized science and technology investigations, that will help pave the way for future human exploration in deep space. Engineers and technicians at NASA’s Marshall Space Flight Center have built the main structure of this hardware that will be part of the rocket when it lifts off from Launch Complex 39B at NASA’s modernized spaceport at Kennedy Space Center in Florida.

The Orion Stage Adapter being designed and manufactured at NASA’S Marshall Space Flight Center in Huntsville, Ala. nears completion.

Jennifer Takeshita, the lead for friction stir welding at Teledyne Brown Engineering, compares a model of the Orion Stage Adapter (OSA), including brackets to secure CubeSats during their spaceflight, to the flight hardware nearing completion at Marshall Space Flight Center.

The Orion Stage Adapter does exactly what its name indicates: it connects the Orion spacecraft to the second stage of the launch vehicle. Using enormous friction-stir welding machines, engineers just finished welding three large panels into a ring that is 18 feet in diameter and 5 feet high. With this welding complete, it’s time for analysis. The main structural ring is currently undergoing nondestructive analysis using 3-D structured light scanning and photogrammetry, which creates a computer model using photography, to ensure hardware was built to design specification.

Three-dimensional structured light scanning, photogrammetry, and solid modeling software are helping engineers visualize the minute differences between the OSA that was designed and the hardware that was built.

Engineers use 3-D structured light scanning and photogrammetry to analyze the main structure of the Orion Stage Adapter (OSA) at Marshall Space Flight Center. Targets for the optical scanner and SLR camera can be seen on the aluminum structure. Solid modeling software will combine the images into a single computer model so engineers can compare finished hardware to the design.

Next, engineers will trim it, weld upper and lower rings onto the large ring, machine it to final dimensions, apply paint, and install the diaphragm, a barrier that separates SLS from Orion. After that, installation of cables and the brackets that will secure the secondary payloads during their spaceflight will complete this critical piece of flight hardware.

The 13 CubeSat secondary payloads will be some of the first small satellites to explore deep space and answer critical questions relevant to NASA’s future exploration plans. These small but mighty scientific investigations include ten satellites from U.S. industry, government, and commercial partners as well as the three CubeSats being built by international partners.


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