Is This The Best Insulation Material For Rockets?

sponsored by brilliant 5 4 3 2 1 something doesn't make sense here this solid rocket motor works but it shouldn't the fuel that's burning inside this thing creates gases that can reach up to 5,000 de F but the tube that holds it together is made of aluminum which melts at a fifth of that temperature how is it possible that this thin aluminum which should melt almost instantly is able to hold up for a 9-second burn and beyond that how is it possible that the motor was only mildly warm to the touch a few minutes after firing the answer is a thermal liner a barrier in between the rocket propellant and the case wall the liner keeps the hot gas from touching the case wall and is usually made of a composite material called phenolic phenolic or more accurately phenolic resin is a nasty substance made by mixing phenol and formal hiide I don't want to overstate this but these two substances are unbelievably bad for you as is often the case the worst a chemical is safety-wise the better it works for Rockets I'm looking at you Florine anyway folic is used all over the Aerospace industry because it's so good at managing heat one place you'll find it is in heat shields for spacecraft hey you want to go to a tangent with me we'll talk about Rocket Motors in like a second but come on let's go in a tangent let's live a little let's talk about spacecraft heat shields so the main goal of a heat shield is to keep the hot plasma that forms unre entry from damaging or destroying the spacecraft there are several ways to tackle this problem and I'll address two of them two of them now one is a blade of insulation and the other is refractory insulation we'll start with the second one refractory insulation usually looks like using lots of black tiles on the surfaces that see the most Heating and it's what got used on the space shuttle X-37B Dreamchaser and now Starship the insulation comes in several layers and I will open up on shape to give you a quick cross-section the top layer must have an extremely high melting point it must be able to survive the temperature seen on re-entry and according to this paper from the FAA the shuttle surfaces on re-entry could reach up to, 1500 C or 2700 F the top layer is typically made out of boraas silicate glass among a few other things and it has a melting temperature of around 1650 C or 3 000 F just beyond what the shuttle tile saw for heating the trick with refractory insulation is that the heat isn't so much dissipated as it is managed the glass surface can get as hot as it wants but we also need to hold on to that glass using a material that won't melt and for that we use Silica fibers these fibers are very thin on the order of several microns and they're space far apart to create a very porous material leading to a heat shield that is upwards of 90% air in the case of the Space Shuttle at the bottom of the tile those fibers transition to a denser formulation which then gets applied to a strain isolation pad and then to the shuttle airframe using two layers of RTV or room temperature Vulcanizing silicone so when I say that the heat is managed but not dissipated what I mean is that while some black body radiation occurs to remove heat or energy from those tiles mostly the goal is to keep that heat physically separated from the airframe of the spacecraft using the air in between all of those silica fibers again the surface can get as hot as it wants because we hold the surface far away from the spacecraft so we don't damage it in an Ideal World this means that the heat shield can be reused for many flights and that's why it was used on the space shuttle which like for many reasons was not quite as reusable as we had hoped that said another Endeavor into full reusability is Starship so let's take a slight tangent off of this tangent to talk about Starship last week's test flight if4 was the first time a Starship has made it all the way through re-entry albeit with some damage along the way thanks to these live views on re-entry we can learn something interesting about spacex's heat shield on re-entry we get these beautiful plasma flows and as things get a little hotter the color of that plasma changes now we don't know all the details on the recipes SpaceX uses to create these heat shield tiles but we can be reasonably sure it's not far off from what was used on the space shuttle the changing color tells us two two interesting things combined with the debris that begins coming off the heat shield is likely transitioning from managing the heat to getting damaged by the heat my granddad used to say that anything Burns if it's hot enough and these tiles are burning Boron compounds burn green and are most certainly found in borosilicate glass which contains Boron trioxide if you are curious why the color of the plasma changes that's why the borosilicate glass on the heat shield tiles is burning off which creates a green flame relatedly this is the same reason you see a green flash at engine startup for liquid Rockets a mix of triethyl aluminum and triethyl Boran is injected into the chamber to start combustion and then trimethyl borate a boron compound causes that flash to be green did I add that part of the script because I wanted to say big words to sound smart yeah of course I did let's get back on track let's say we're coming in too hot and the entry heating will melt any type of refractory insulation how do we prevent the spacecraft from getting damaged actually the solution is to let the spacecraft get damaged or rather let the heat shield get damaged this is referred to as oblation which is where we slowly burn away the heat shield on re-entry this is a complex process and I've prepared a demo to show you how it works first let's talk about the material involved we're back to phenolic now the same material that I was talking about earlier as a thermal insulator for Rocket Motors the phenolic resin is made of phenol and formaly and it's a liquid that can be infused into a flexible substrate like fiberglass linen canvas carbon fiber and others this means that while the resin itself isn't a great choice as an ablative we can take that resin Infuse it into a substrate material to make it stronger and then cure it to form a hard block you can then take that hard block cut it to the shape you want and use it in a heat shield to protect your spacecraft as it re-enters Earth's atmosphere so what makes this material so good at what it does I thought about making like a drawing or a sketched out cross-section for this but then I remembered I have the material and I have a blowtorch let me just show you [Applause] this is a piece of linen phenolic that I cut out of the Simplex V1 rocket nozzle a year ago I saved that scrap material and figured I'll probably never use this and I can't describe the joy it gives me to know that today I will use it after blasting the felic with a blowtorch for about a minute I cut it in half on the band saw and now we'll clean it up and check it out under a microscope all right we're at the workbench I've got my digital microscope and the top down camera with the folic rounds let's take a look at these things actually before we get into the microscope I do want to make a quick mention the phenolic pieces have a little bit of grease on them so there are parts or sections that look darker these are not because the material has been affected so much as it's just like contaminated with grease so not everything we look at here can be directly attributed to the ablation okay microscope time so starting out with the top layer here this is the charring that happens now this Char layer is made up of Amorphis carbon for the most part when the phenolic resin that's in this Matrix this linen phenolic Matrix when the resin and the linen burn off um they leave behind some deposits um and that's what this that's what this charring is It's the carbon in there that does not burn it just like sits on the top and then the rest of the components of that phenolic resin off gas and they are part of the reason that this phenolic material is such a good insulator they're not totally attributable for that though it's actually kind of a shared Duty and we'll get into that in a second before we zoom in further I want to talk about the bubbles in this material here and the little Pops that you heard when I was hitting it with the gas torch I think this has to do with the quality of the material if I had to guess the manufacturer probably got some air pockets with moisture or just water in there uh or any type of you know gas or liquid that can expand when hit with heat um so if you have air pockets with a little bit of moisture or something something that can expand a bunch that's probably what's causing these little explosions in the material and I think that's mostly due to the quality of the material um also the direction of that bubble coming out you see the bubbles aren't coming out to like to the side or whatever that also has to do you know I think that is pretty consistent with like the layer Direction here and you can see smaller versions of it down here um there are just small little delaminations that happened because there's probably like a little air pocket that gets trapped in there the second thing that I want to look at and I'll take the other piece of material for this um is this finel section right here so this is where the Char layer comes off and this is a good time to talk about how this Char layer is weekly attached and I don't mean it's attached every 7 days I mean that this thing comes off with basically you know if you like look at it the wrong way so I'll just tap it with my screwdriver and I can just remove it it's extremely easy for me to remove this this is a weekly attached Char layer so all of this Char is mostly Amorphis carbon as I understand it there's probably some other stuff in there and it's possible I'm wrong I'm fairly far out of my depth on this but um the Amorphis carbon as I understand it is basically a jumbled up mess of these molecules instead of a nice crystallin structure like you would get with graphite as a good reminder graphite is just a form of carbon carbon fiber is another form of carbon um when they say it's a gem motor graphite epoxy motor right the graphite is the carbon granted there are lots of different grades we're not going to get into the Weeds on this but this Amorphis carbon um is part of the reason that this is such a good insulation material because when you form this layer um especially because of the structure of the carbon there's a lot of empty space in there so it it makes a good insulator once again kind of like the refractory insulation we're using air as the insulator and then we manage the heat with something that can take it this carbon isn't going to melt it will strip off again it's weakly attached right but it protects the layer under it and it does a pretty good job because I hit it with this torch for quite a while and even like a little bit down below all of this folic material is mostly fine okay let's see if we can zoom in a little further I love this you should absolutely buy a digital microscope if you can it's like totally worth the money and I think this is like under a 100 bucks on Amazon too okay what are we looking at here there we go so this is a very closeup shot of the phenolic material this is right at the edge you can see the edge of the material right there and then you can see where the Char layer forms so this is an interesting specimen because it's not just the top layer um but any part that's getting hit with heat is going to start charring um now another word for this is pyrolysis um it pyrolyzes and that's just giving off the gas leaving behind that carbon and a couple other things again if I'm wrong on this let me know I mean be nice about it but like let me know in the comments I could be wrong and then you can see the untouched resin below here so there's the Char layer that's got all of that amorphous carbon it's got all of the you know there's a bunch of air in that section at this point and that protects the layer that's below it I'm just going to poke around here for a little while there's so much interesting detail that we can see here on this Char layer uh and otherwise like if I move around over here yeah there we go look at that so this is a beautiful like interface between the Char and the actual phenolic resin so anything that looks tan or brown that's the untouched resin or the unburnt resin and anything that's black or darker brown um that's when it's starting to pyy and burn and then all of these Little Fibers these are part of the linen this is part of the linen mixture the linen substrate that's holding it together better than just the resin would like resin anyone who works with resin or epoxy or or two-part glues knows that on its own the tensile strength is not great so we have to include some type of substrate to give it better material properties and that's what the um Linen in this mixture is doing you don't just have to use linen though I think I mentioned this before but you can use canvas you can use fiberglass um SpaceX it infuses a bunch of this phenolic resin into a carbon fiber structure I think it's called fiber form here's another interesting shot this is a top down look between the Char layer and the untouched layer again the Char layer um just easily comes right off I bet I can get more to come off if I just do this yeah there it goes I think I heard it Splash in the other side of the room but the Char layer is weakly attached and I think we should probably have a conversation about this in the next few videos about Simplex where we're going to talk about Mass flux and how important Mass flux is to oblation because that makes in my opinion a much bigger difference than the actual heat that the material is subjected to so we'll get to that if you're itching to hear about it don't worry I also want to take a look at the other side of the folic here which is uh Untouched by the flame um but gives you a better sense of that linen substrate that linen substructure and it's interesting to compare um you know it's it's interesting to see this is this is truly just a composite structure so uh this is the bottom of the linen phenolic right here this is Untouched by the flame both sides are Untouched by the flame this side is the side that got cut with the horizontal Band Saw and this side is just pure what it looks like when it came from the factory and you can tell that this is truly just a composite material um because this side is extremely smooth and that phenolic resin is the main ingredient on the top I don't feel any of that linen substrate CU you can imagine when you lay up a composite material like this you usually use a little bit more resin than you do the substrate um and that's good for us here because the phenolic is the thing that creates most of that Char but the bottom bottom surface is smooth just like if you were doing a carbon fiber or fiberglass layup and you had a little bit extra epoxy that floated to the surface or that came to the bottom it's quite pretty to look up close at this linen substrate um it's clearly got a basically 0 to 90° uh weave in it and the linen is pretty thick which is worth noting you know this is not quite what we'd see for a structural composite but again as I said earlier like I'm not buying the Toof Shel material we don't really need a lot of structural Integrity in this material we just need that phenolic resin one thing that's also probably worth mentioning in this process is the safety uh when working with this stuff so uh as I said earlier it's phenol and falahi that you combine to make this phenolic resin and that in its form and it's like liquid form is really bad for you it's not it's not good don't mess with it most people aren't making their own phenolic composits it's more of an industrial process um but once it's in this solid solidified and hardened form it's not as bad to work with if I'm just holding this here my main concern actually isn't the phenolic at all it's that Char I don't want to create a bunch of dust and then breathe it in but where you do start to get concerned again is when you're working with the material on a machine so if you're cutting pieces off you're going to create some of that dust whether it's fiberglass dust carbon dust you know any type of uh composite dust when you're Machining it or cutting it um that stuff cannot be breathed in so you've got to wear a respirator for that process um this is a bit of a spoiler but this is the simplex V2 rocket nozzle I took cross-sections of lots of the Simplex V2 Parts um and I think I'm going to do a video where I just do a top down and microscope explainer of the whole cross-section so I'm going to save that for a little bit later but we are going to talk a lot more about felic ablation in that video and how that process works between just the heat soak and the mass flux and the liner itself there's a whole lot to talk about and I think I'm going to save that for one of the next few videos so back to the other version of me all all right hello again so that is a look at a very generic piece of phenolic for heat shields we can get more specialized with it though phenolic composits like this are dense which means they're very heavy for anything that flies on a rocket the goal is almost always to keep it as lightweight as possible which is why in the 8S NASA developed a composite material called Pika the name stands for phenolic impregnated carbon a blader and a spin-off of this material called Pika X is the SpaceX version that gets used on the dragon capsules we can actually find out a decent amount about both of these materials much of it coming from this one research paper that I found on a website that looks like it's the official SpaceX website but is actually a Polish news site about SpaceX anyway Pika and p x are extremely similar materials and their fundamental differences largely come down to the manufacturing process the process begins with a carbon fiber substrate and much like the refractory insulation from earlier on Starship and the space shuttle these carbon fibers are very far apart and very porous the fibers are then coated in phenolic resin which will eventually pyze and form a Char layer that protects the spacecraft on re-entry I couldn't find the substrate carbon fiber material used by NASA when P was developed but the major Innovation from SpaceX which led to a 10x cost reduction was switching to a similar fiber material called fiber form I went down quite the rabbit hole while trying to find out more about fiber form which was developed by a company called fiber materials and who no longer has a website of course that is no match for me because I have the W back machine when I look back at the website in 2021 I can't find a whole lot of detail in fact I see nothing about fiber form but we do see that FMI likes extreme materials they also make these extreme materials for some intense programs these are things like standard missile the Patriot missile Thad and the Trident D5 submarine launched nuclear ballistic missile we talked a bit about itar in the last video and if it's not obvious if we can't find a lot of detail about this material I won't be that surprised but if we go further back to 2017 on the way back machine we can find the same page with info about fiber form this is a material meant for furnace insulation used as a substrate for a spacecraft heat shield it doesn't stop there though I went way back to 2003 to poke around this very old looking website and I found this tons of detail we've got density we've got compressive strength we've got thermal conductivity paracity in all likelihood these are probably details that you could get with a quick inquiry as a customer but it was cool to find that the further back I went the more companies were willing to publish online so that is quite a lot of information about folic and heat shields and I almost forgot we were supposed to be talking about folic liners for Rocket Motors I showed this motor at the beginning and said that it shouldn't work and the reason it does is a Finola actually that's not quite true this was the biggest challenge in terms of propulsion development for the space shot rocket I mixed my own custom liner from bare ingredients and injected it into the case then spun the assembly above a th000 RPM to cast that liner directly into the motor we just went through a whole video on folic insulation and you know what's crazy I don't use any folic in that liner we're able to achieve good results while staying away from bad chemicals in the long run this spincasting approach will save me time money and complexity and in the next video I'll explain how this whole process works even though I'm not using phenolic in the thermal liner that we're going to talk about the reason I made this video is not just because I like going on tangents and talking about heat shields although that's certainly part of it it's that understanding the charring and pyrolysis behavior that folic goes through is an important step in understanding why the next steps we take for the thermal liner are important you can think of this video as a sort of precursor to the next one it'll be important context that said before we get to the next video I would like to thank the sponsor for this video oh hey I didn't see you there I was just spending 15 minutes a day getting smarter what's that you want to learn how you can do it well you can use today's sponsor brilliant you are not going to be able to see that the sun is way too bright brilliant has become a longtime sponsor of this Channel and it's because I love what they do it's an active platform built around the idea of learning by doing the most effective way to break new ground in your 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Channel: BPS.space

Views: 238,226

Keywords: BPS

Id: UkLExdiz8jY

Length: 22min 38sec (1358 seconds)

Published: Wed Jun 12 2024