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Rocketology Research Paper

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.

“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.

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.

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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Key concepts
Chemical reactions
Physics
Gravity
Rockets
Thrust
Pressurization

Introduction
Have you ever marveled at how fireworks, toy rockets or real spacecraft can launch into the air? It can be an amazing thing to witness. It is thrilling to see something lift off against Earth's gravity. The strong push required to launch a spacecraft comes from a chemical reaction in its rockets. This means that every time you see a spacecraft launch, you're watching chemistry at work. In this activity you'll get to blast an object into the air using two simple household ingredients: baking soda and vinegar. Investigate how to mix these chemicals to get the best lift off, and then this Independence Day you could give your family a homemade, gravity-defying show!

Background
How does a spacecraft lift off and get into space? The simple answer is that it has rocket engines that propel it. The rockets depend on combustion to provide the thrust the spacecraft needs to overcome the force of gravity and climb into orbit. Combustion is a fast, exothermic chemical reaction between a fuel (for example, jet fuel) and an oxidizer (such as oxygen) in which the fuel burns and heat is produced. Usually the fuel is an organic compound (containing hydrogen and carbon, and sometimes metal and/or other components). During the chemical reaction, new compounds are made. These are referred to as the exhaust. The rockets push the hot exhaust out from the bottom at high pressure and thus the spacecraft is thrust upward.

In this activity instead of using rocket fuel you will use baking soda (sodium bicarbonate) and vinegar (acetic acid) to make a different kind of chemical reaction that can launch a small-scale rocket made from a film canister. The reaction produces water and carbon dioxide (which will appear as bubbles). You'll take advantage of the pressure the carbon dioxide gas makes in the capped film canister to launch your rocket.

Materials
• Plastic film canister with a lid and tight seal. Fuji or Kodak canisters should work.
• Baking soda
• Measuring spoons
• Wax paper or bowl
• Spoon
• Water
• Vinegar
• An open outdoor area at least two meters from buildings. It is ideal to have a hard, flat surface such as a paved patio or driveway.
• Safety goggles
• Rag or paper towel
• Optional: Construction paper, transparent tape, stickers and scissors
• Optional: A helper to watch, a helper to take a video or a video camera with a tripod

Preparation
• If you like, you may decorate your film canister rocket. You could wrap a piece of construction paper around the canister and cut the paper so it just covers the rocket's sides (but does not go above or below the sides). After evenly wrapping the paper on the canister, secure it with some tape. You can add additional flat decorations, like stickers or drawings. Make sure it is still easy to put the lid on.
• Remember, when you launch your film canister rocket be sure to wear eye protection and exercise caution!

Procedure
• Place one teaspoon (tsp.) of baking soda onto the wax paper or bowl. Add one eighth tsp. of water to the baking soda and mix it in well. If you're using wax paper, you can carefully use the wax paper to fold the damp baking soda onto itself to help mix in the water.
• Turn the film canister lid upside down and pack the inside of the depression with the damp baking soda. (Do not put baking soda near the rim where the canister snaps onto the lid.) Pack it tightly. Turn the lid right side up again for a moment. Does the damp baking soda stay in place? If it stays, move on to preparing the vinegar. If it falls out, add a little bit more water to the baking soda and mix it in, but try to add as little water as needed. The baking soda will not need to stay packed into the lid long.
• Add one tsp. of vinegar to the canister at a time, filling it almost to the top. You need to add as much vinegar to the canister as possible—just enough to keep the vinegar and the baking soda from coming into contact when you later snap the lid onto the canister. Depending on the canister, this may be about five tsp. of vinegar. How much vinegar did you use?
• Go outside to an open area at least six feet from buildings. If you want to videotape the reactions, set the video camera so that it has in its viewfinder the spot where you will launch your canister rocket and the equivalent of at least the first story of a building and then start the video. (Alternatively, you may have a helper watch the reactions to help you figure out how high the canisters go.)
• Put on your safety goggles. Stoop down near the ground on a flat, hard spot and quickly snap the lid onto the canister to seal it. Immediately turn the canister over so the lid is on the ground, and quickly move away. Wait for the chemical reaction to occur. How long does it take to happen? When the lid pops off, the rocket should launch. How high does the canister go?
• Tip: If the rocket did not launch, the lid might not have been sealed tightly enough. (If this happens you may simply see many foamy bubbles coming out of the canister.) The rocket may not have launched right for some other apparent reason (such as not sealing the lid fast enough). If it didn't launch right, try preparing and launching the canister rocket again. You may need a little practice to get used to launching the rocket.
• After the launch, carefully rinse the lid and canister with water and then dry them. If your canister is covered by construction paper, make sure it doesn't get too wet.
• Prepare the damp baking soda and vinegar as before but this time use a little more than half the original amount of vinegar. For example, if you used five tsp. of vinegar, this time use three tsp. (Still use one tsp. of baking soda.)
• Again, go outdoors, put your safety goggles on and launch your newly prepared canister rocket. Does it take longer, shorter or about the same amount of time as the first rocket did to launch? Does it go a higher, shorter or about the same distance?
• Lastly, rinse the lid and canister with water, dry them and prepare them as before but this time use one tsp. of vinegar (or around one fifth of the original amount that you used). Put your safety goggles on, go outside and launch the canister rocket. How long does it take to launch compared with the other two launches? How high does the canister go compared with the previous two times?
• If you're unsure of any of your results, you can try repeating them (using the same amount of baking soda and vinegar).
What amount of vinegar led to the highest launch height? Why do you think this is?
Extra: You can try varying the amount of vinegar even more and see how this affects the rocket's launch, such as using one, two, then three tsps., etcetera, of vinegar. (You could also repeat the same conditions you tested to see how consistent your results are.) How does changing the amount of vinegar in the canister change how it launches?
Extra: You could also try changing the amount of baking soda (keeping the same amount of vinegar) and see how this affects the canister's launch. For example, you could try comparing one, three-fourths, one-half and one-quarter tsp. of baking soda. (Adjust and use just enough water for the baking soda to stick to the depression in the lid.) How does changing the amount of baking soda in the lid affect the canister's launch?
Extra: Add a cone and fins to your rocket (such as out of construction paper) and launch it again using the best conditions you found. How does adding these components affect the canister's launch?

Observations and results
Did the launch using the smallest amount of vinegar result in the highest launch height? Did it also take the most time to launch?

When baking soda and vinegar are mixed together, the reaction produces water and carbon dioxide gas. In the capped film canister, the carbon dioxide gas builds up until the pressure of all of the contained gas causes the canister to pop open. The pressurized carbon dioxide then quickly escapes the canister through the open bottom. This is how the chemical reaction provides the thrust the canister needs to launch. You may have noticed that when the least amount of vinegar was used, it took a little longer to launch than when more vinegar was used. Because there was less vinegar in the canister, there was more space for carbon dioxide gas to fill. It takes longer for more carbon dioxide to be made from the reaction and thereby more is needed to fill this larger space and build up enough pressure to pop the lid open like it did before. Overall, when the least amount of vinegar is used, more carbon dioxide can fill the canister and a higher launch height should be seen (possibly around 15 feet, compared with around six feet when the canister was nearly full of vinegar).

Cleanup
If you launched your rocket on a concrete surface, spray the surface down with some water after you have completed your launches.

More to explore
Rocket Thrust, from the National Aeronautics and Space Administration (NASA)
Combustion, from NASA
Baking Soda and Vinegar Reaction and Demonstrations, from apple-cider-vinegar-benefits.com
Rocketology: Baking Soda + Vinegar = Liftoff!, from Science Buddies


This activity brought to you in partnership with Science Buddies

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