NASA's clever technique to make combustion chambers

So imagine this, it's the 1970s and you're an engineer at NASA, not just any engineer, you're literally a rocket scientist. Rocket power is the key to greater achievements in space. Designing the next generation of high-performance rocket engines. What are you working on. Now it will eventually go to the space shuttle, except you need to

make

something that is impossible to

make

with traditional tools. The year was 2023. You could just 3D print it in metal, but that's not an option because it's the 70s and 3D printing in metal isn't. It doesn't exist yet, so it's time to get the wax out of your secret weapon.

Yes really. I mean, they used fancy wax, but essentially it's candle wax and it was absolutely critical to making the most important part of the space shuttle engine, the main

combustion

chamber. I've been in love with this

technique

since I first heard about it, so I decided to make my own scale model of the main

combustion

chamber to demonstrate how the

technique

works. First, we probably need a quick crash course on the design of the rocket chamber and how it works. everything works I'm definitely not a rocket scientist so this is just a very high level overview so we're all on the same page, most people are probably familiar with the large bell shape at the bottom of a rocket engine, is the most iconic and A notable part of any rocket we are talking about today is directly above the bell.

The section up here is known as the main combustion chamber and is where all combustion originally takes place through combustion in the thrust chamber. Large amounts of energy are released. Not unlike the combustion chamber inside a car engine, we mix fuel and oxidizer and ignite it to create some type of force that we use. Hot expanding gas escapes through the throat of the nozzle, unlike a car engine, the temperatures and pressures inside it. The main combustion chamber is truly amazing, talking over 3500 degrees Celsius and the pressure is over 6000 pounds, so if you want to keep your combustion chamber from melting into a puddle of metal, you need some way to protect it. or actively cool it, there are many ways to do it, but the most common technique is called regenerative cooling, where the fuel or oxidizer is pumped through channels or tubes along the surface of the combustion chamber to remove heat and keep it.

Everything from melting it down is like water cooling a PC, except you're using cryogenic liquid hydrogen. Instead, Everyday Astronaut has a really good video on this topic that explores all the different ways to cool a rocket, so if you're interested in more details on that. Check out the link below in the description, so in the early days of spaceflight, if you wanted to use regenerative cooling, you often ran thin pipes along the outside of the combustion chamber and the pipes are what made it flow. refrigerant throughout the system to remove it. Heat, this is the method used in the F1 engine of the Saturn V rockets and here you can see the tubes that go up and down the nozzle and extend to the main combustion chamber.

The fuel is rooted through the many tubes that are stacked together. In this way, the fuel cools the chamber and protects it from the high temperatures of the internal combustion gas, but this technique has some problems. It is relatively heavy because you have thousands of extra steel tubes that you need to attach to the engine, which adds a lot of extra mass, the brazing process creates thousands of joints that need to be inspected to make sure they are all absolutely perfect and, thermodynamically, , is not so ideal. You have the heat that needs to be transferred through the chamber wall and then through the pipe wall before it can reach the coolant, ideally we would have those coolant channels built right into the chamber itself so it is one piece monolithic, it would be a simpler system, lighter and would cool better, it is a win-win situation, unfortunately it is like that.

It is also impossible to machine in a conventional way. The machines used by machinists are called machine tools. The internal cooling channels that conform to the shape of the chamber are impossible to drill with straight drills and bent drills just don't work as well for some reason, so NASA. and their contractors came up with a pretty brilliant solution to this problem and they did it using a technique that is similar to the original additive manufacturing before 3D printing existed, so we're going to machine a replica of the combustion chamber and then analyze it. The process on how it works.

Thank you. This is a moderately faithful replica of the main combustion channel of the RS-25 engine. The motor used on the space shuttle is made of copper like the original MCC, but there are some differences that I machined. from a single piece of copper, but that wouldn't have been remotely possible for the space shuttle - given the size of the engines, it would have been prohibitively expensive to machine it from a single piece. Instead, they used a vacuum melting and centrifugal casting technique. To obtain the rough casting which was then machined to final dimensions, the shuttle also used a special copper alloy known as narloy z, a mixture of copper, silver and zirconium.

Copper is used because it transfers heat very well, but pure copper is not strong enough to use. In the main combustion chamber, Narloy Z was developed to provide a stronger alloy, silver and zirconium help to strengthen the copper and make it resist the forces involved after the chamber takes on its characteristic hourglass shape. Thin grooves were machined along the outside of the chamber. are the coolant slots that will allow the liquid hydrogen to flow up and down and remove heat, but right now these are just slots and we need closed channels, so the next process is known as closure, where we form a layer outer or jacket. top of the copper inner core, this is a two step process and the first step is where we use our secret weapon wax.

A rigid, machinable wax is melted into the channels and then carefully scraped and sanded by hand. The purpose of this is to fill I move up all the channels and make a smooth, continuous profile along the outside of the chamber. I use jeweler's wax which is a very similar type to what they used, it is hard and machinable and not rubbery like beeswax would be, it ended up being quite a challenge. work at this scale because wax doesn't really adhere well to metal and the grooves are so thin there's just not much material to grab on to so I've spent about my entire life melting wax into these grooves by carefully filing the sanding Scraping it off and then coming back to fix all the spots where the wax had come off and needed to refill a channel, so it was very tedious, but I finally got a completely covered surface with which we can move on to the next step.

I did too. I tried using superglue that was thickened with fumed silica or graphite and it worked fine; It certainly adheres better to the metal, but removing it in the end proved to be quite a challenge, so wax ended up being the best method once the grooves were finished. The next step is to create the outer jacket using electroplating. If you're not familiar with electroplating, I have a previous video where I used it to strengthen 3D prints and it does a good job of explaining it from a technical perspective but from a high point of view.

On a level, you can think of electroplating as a special solution that contains metal ions and when you apply an electrical current, the ions come out of the solution and deposit on what you are trying to electroplat, essentially forming a small, thin layer of metal. It works with a handful of different metals, but the main ones used are copper and nickel. Copper is typically used because it is quite conductive and also plates very easily so it can be used as a base layer and nickel is a relatively rigid and strong metal. so it is good for durability purposes.

NASA first used a very thin layer of copper followed by a very thick layer of nickel on top. The copper acts as a shield to prevent hydrogen embrittlement of the nickel and steel layers on the outside. Liquid hydrogen flows through these. The channels will weaken the nickel and steel over time, making them structurally unsound, and you don't really want that in a rocket engine, so the copper X is a small protective layer to prevent hydrogen from escaping. The nickel layer that sits on top is the main structural layer and they plated it quite thickly to provide enough strength for the chamber, so I dropped my model into a bath of copper electroplating and let a thin layer form. copper layer on the surface;

You can see it spreading through the wax here, but wait if you're familiar with electroplating. You know that coating only works on conductive surfaces and wax is definitely not conductive. So how does it work best? I can tell that NASA polished a fine silver powder on the surface of the wax, which made the wax conductive. This technique is also used in other engines like the Vulcan in the Aryan 5 and I saw in a documentary that its wax was black which I'm not sure about but I guess that means it's filled with graphite to make it conductive so I followed that. technique and doped my wax with a bunch of graphite powder until it was reasonably conductive.

It has enough conductivity to allow the copper to spread across the surface and once you have a thin layer it doesn't matter anymore and it just builds up. From there, I left this board for a couple of hours, took it out, rinsed it, and put it in the nickel plating bath. Then this takes a long time, so NASA put an inch or two of nickel on the surface of their chamber and most of the coating. The dips settle at between 20 and 30 micrometers per hour, so you can imagine how long it takes to accumulate one centimeter of material.

I plated mine for 24 hours, then took it out and machined the surface to see how much more filling was needed. all the gaps and I realized that we had quite a bit of work to do, so I repeated the process a few more times, totaling I think about 72 hours in the plating bath and you can still see that even in the end we don't have a very uniform but, although it is a little ugly, it closed the surface and I think we can continue with the final step which is to remove the wax from the channels.

When I started this project, I originally assumed that NASA just melted the wax because that seems like the most logical thing, but I actually found a document that said they dissolved it with perchloroethylene, which makes sense: you want to make sure that all the wax comes out without leaving any kind of carbon residue from a burning or melting process even though I tried melting it first because it seemed like the easiest thing to do on my scale with this little replica and it worked but it didn't remove all the wax so I ended up trying too dissolve it chemically using xylene and hot oil like canola oil, but I finally managed to clean the channels and we can see the final result.

It's definitely not as polished or professional as what Nasico produces. It's a little ugly, but honestly, I'm really excited this worked. It's really cool to see that layer of nickel on the outside bonded to the copper with just a hollow channel in the middle. I think I ended up depositing about 500 microns of nickel and machined it down to about 300 microns all the way around. It's great to think. This is the exact same process used by NASA and Rocketdyne to make the RS25 engine much larger and controlled in a much better way. It's actually a very

clever

and ingenious method when you think about it.

Engineers were able to make a monolithic combustion chamber with internal conformal cooling channels at a time before 3D printing existed, it's pretty cool. I had some leftover material that I wasn't really going to use for anything, so I decided to just machine some more of these. The cameras aren't really useful for anything, but they make a cool little desktop widget or maybe a gift for a fellow space nerd. I only made a handful, but if that sounds like something you might want to purchase, there's a link below this technique. Not without its downsides, as I mentioned it's quite slow and requires a lot of manual labor on the part of humans to scrape, polish and sand everything.

Galvanized metals can have a fairly significant amount of tensile or compressive stress depending on the composition of the bath and on one. From my first few attempts you can see that I didn't coat the nickel thick enough and the internal stress of the coating actually caused it to peel away from the copper core. HeNew SLS rocket that recently had its maiden flight is also using the RS-25. engine like the shuttle, but Rocketdyne has modernized some of the features of the engine, including the main combustion chamber, instead of using this type of tedious electroplating process, they are now using something known as hot isostatic pressing, which uses heat and intense pressure to bond a prefabricated outer jacket to the copper core, this is much faster and requires less human hand to perform the process and also generates a stronger component, making it a better technique even though NASA has left of melting wax and galvanizing it.

It has a special place in my heart because it's a great example of intelligent problem-solving to work around manufacturing limitations, and I think that's ultimately what I love about manufacturing: it's often an accumulation of little tips and tricks. and creative problem solving to build the thing you're trying to build and once you know a tool or a technique, it's in your toolbox forever, you can use it in future projects. I was recently doing something where I electroplated diamond on custom ground tools for a glass machining project I'm working on if that sounds interesting to you. I posted a video about it on Nebula.

Nebula is a streaming platform created and owned by content creators and is a place where we can post whatever we want without having to please an algorithm. This diamond electroplating project is a perfect example. Honestly, I've been watching this footage for years, so this is my quick, super crazy setup to see if this idea would work. It was a little strange for me to be milling carbide. The next step is to electroplat this with our nickel diamond suspension and then put it on the CNC and press the Go button and I just couldn't edit a video about it because it's too small and too specific to work well on YouTube, given the limitations of the platform and the time spent editing.

That video together could have been better invested in a project with a broader appeal and I don't have a team, it's just me so I have to be careful what I choose to do on YouTube, but now that I've joined. nebula I actually have a reason for posting these videos. I mean, it's still a small, niche topic like that isn't going to change, but people watching it on nebula help support the channel more than ads on YouTube would given the size of the project. of course there are tons of other creators on nebula practical engineering real engineering strange parts bobby broccoli wendover as the list continues I know you will probably like them because I watch all these channels myself nebula has no ads many creators publish exclusive content on nebula and there are a number from other features like classes, newsletters, and podcasts, yes, cereal is better without milk.

If that sounds interesting, there's a link below that helps support me directly and gives you a pretty good discount. I think it's like 40 off and if you sign up. for the annual plan it's only two dollars and fifty cents a month. I'm still working on a lot of cool things for this channel on YouTube and I'm really excited about some of the projects coming out in the future, so I guess that's all I have for you thanks for watching see you next time