What are Hypergolic Rocket Fuels? (Other than Explosive, Corrosive, Toxic, Carcinogenic and Orange)

hello it's scott manley here with another episode of things Kerbal space program doesn't teach you I regularly talk about hypergolic propellants they are a core concept in rocket science propellant combinations that when they are mixed they spontaneously combust meaning that rocket scientists can get away without ignition systems that might fail this is of course at the expense of the lucky people who get to handle the propellant loading for the rocket so I wanted to talk about hypergolic fuels in a bit more detail the most common form of hypergolic oxidizer is dinitrogen tetroxide of course most people that actually use the stuff choose to save a syllable and they say in nitrogen tetroxide instead even though that's not technically correct the molecule consists of two nitro groups that is the nitrogen atom and a pair of oxygen atoms and these two our groups are joined by a single weak bond between the nitrous the nitrogen's and in fact in liquid that bond can actually be rather weak and it will break and reform the nitrogen dioxide is brown while the nitrogen tetroxide is clear so near as freezing point the liquid is basically clear but as it warms up more and more that disassociates or breaks down and you get a browner and brown or liquid and of course when the stuff spills and you get a big orange cloud that orange is coming from nitrogen dioxide nitrogen tetroxide generally isn't used as a hundred percent pure propellant it's usually mixed with other stuff in the Apollo spacecraft for example they added one percent nitric oxide primarily to make it less corrosive this was referred to as green nitrogen tetroxide but in modern spacecraft it's referred to as mixed oxides of nitrogen nuts nitric oxide nitric dioxide and dinitrogen tetroxide usually this is abbreviated to mo n and with a number to indicate the percentage of nitric oxide is being added for example the space shuttles orbit maneuvering system used mon 3 and if there say I need to lower the freezing point from minus 11 Celsius to something more useful for space travel 125 will give you liquids down to about minus 55 centigrade that's your oxidizer over on the fuel side you have the hydrazine family of chemicals your basic hydrazine consists of a pair of nitrogen atoms with four hydrogen atoms hanging around the outside technically it could be called tetrahydrate or Die nitrogen but nobody would ever do that because it's hard to say but that's the least of your problems because it's not stable either with just a little bit of prompting it'll happily split apart into hydrogen nitrogen and ammonia and release a fair amount of energy in the process for this reason hydrazine is actually used as a mono propellant by passing it over a heated catalyst bed to drive the decomposition so the gasses can exhaust out a nozzle and give you attitude control on your space probe but hydrazines first used as a rocket fuel was in the Messerschmitt Amy 163b Comet the rocket propelled fighter seen in World War two the the sub the fuel for this was see stuff which was 30 percent hydrazine 57 percent methanol and 13 percent water well the Tishkoff oxidizer was about 80 to 85 percent hydrogen peroxide cut with the water so pure hydrazine generally isn't used in by propellant combination because it's tendency to decompose means that it can be used for regenerative cooling and also it just under the right conditions can spontaneously explode also it's freezing point is about two degrees Celsius which is inconveniently high for many applications so instead we have mono methyl hydrazine this replaces one of the hydrogen atoms with a methyl group that is a carbon and three hydrogen atoms this lowers the freezing point down to minus 52 Celsius and makes it far more stable these benefits do come at a cost you get a little less performance compared to pure hydrazine also the density is a little or so you need larger tanks monomethylhydrazine and mixed oxides of nitrogen are used in bipropellant reaction control thrusters on the dragon in their Draco thrusters and the space shuttle the sickness and many many other spacecraft but MMH is still not stable enough for those big regenerative Li cooled rocket engines so to make that work you need to replace another one of those hydrogen atoms with another methyl group to get dimethyl hydrazine except you very specifically want the unsymmetrical version or udmh unsymmetrical means that you have one nitrogen atom that has both methyl groups while the other nitrogen atom has just the two hydrogen's the cemented version splits the methyl groups either way but it's not desirable in rockets because the symmetrical version has a melting point of a bit minus nine centigrade whereas the unsymmetrical version has a melting point of minus 57 and therefore is way better if you're working in cold areas udmh is stable enough to be stored for years without any chance of decomposing and it was also stable when you're trying to cool the raging inferno inside your rockets combustion chamber in exchange you do give up a little more specific impulse and its density is also a little lower than even MMH so udmh and NT or both together uses propellant combinations in the Russian Proton rocket India's PSLV and China's long march two three and four and a number of other rockets out there however there is a fourth option that has also been used in the past it's known by its trade name of Eruzione at 50 and it's made by mixing 50% hydrazine with 50% udmh this actually gets a better specific impulse and density than udmh it gives you a lower melting point than pure hydrazine and is stable enough to be used on large engines aerozine was the fuel used by the titan rockets and it was also used by the upper age of the Delta - and the main engines on the Apollo command module and the lantus end engines on the lunar module aerozine of 50 was of course a made-up name it was designed and developed by Aerojet and turns out that mixing these two things together isn't as simple as you imagine if you just take the two chemicals and put them in a big bath and stir them the wife's attempt to stratify because the dent mid difference in the density is about 20% so Aerojet had to develop a mixing system or a blending system and it was very similar to the way fuel injectors and rockets work they would have vents or nozzles that would spray into each other and create a cascade of very small droplets which would then ensure very thorough mixing and therefore a stable mixture however as of right now I think we've stopped making and the last time it was used was on the second stage of the very last Delta tube which launched icesat-2 back in 2018 so those are the main hypergolic propellants in use today but in the past we've seen and few other notable compounds in particular before nitrogen tetroxide was all the rage nitric acid was where was that it was the oxidizer of choice and this stuff that you may have to deal with in chemistry class is heavily diluted with water but when you use nitric acid in rocket propellants it will be 100% with just the acid and at these high concentrations the acid will actually decompose into nitrogen dioxide and water and that makes if you have pure stuff is called white fuming nitric acid and the fumes coming off are nitrogen dioxide I'll pick up a little bit of a yellow cast from dissolved nitrogen dioxide and early on in the development the engineers realized that you could take white fuming nitric acid and add 13% dinitrogen tetroxide and get red fuming nitric acid which had better performance overall and then the real eye the engineers realized that actually it was the nitrogen tetroxide that was doing all the work and it was much better overall the corrosive qualities the nitric acids would just be a big problem overall so they would attack fuel systems that valves the tanks and so they had to add inhibitors to them so this is where you would get inhibited fuming nitric acid typically an inhibitor is something like hydrofluoric acid and while that sounds a little crazy to add an even stronger acid what happens is that very weak 1% hydrofluoric acid attacks the vulnerable areas and then creates a very thin fluoride layer that protects it from the nitric acid so this creates a whole insoluble barrier that protects all your components overall and apparently North Korea have had issues with this some of the wreckage that has been recovered had failures that were related to the fact that they weren't using inhibited red fuming nitric acid nitric acid has been used as an oxidizer with many fuels hydrazine udmh turpentine furfural alcohol there's something called tonka it's still seen in many old military missiles but even the likes of North Korea and Iran have stopped using it for their launch vehicles and moved on to nitrogen tetroxide so it's basically obsolete by now so anyway all of these propellants are horribly nasty things to be around not only are they designed to burn with great fury they are corrosive they are toxic and very likely carcinogenic handling them requires teams working with self-contained pressure suits and not only does that take extra time it takes extra money making them less desirable as cleaner options have which you have come in and replaced them the u.s. stopped flying Titan in 2005 and Russia is kind of in the process of phasing out the for the proton but you know because you know rp1 and liquid oxygen are a lot easier to clean up when they are spilled so in the long term I don't see any huge breakthrough in propellant chemistry which will improve upon the hydrazine nitrogen tetroxide combination while we have new clean more Palance there's not really the same opportunities for clean hypergolic propellants so we'll be seeing these for a long time to come I'm Scott Manley fly safe [Music]

Channel: Scott Manley

Views: 253,447

Keywords: rockets, rocket fuel, nto, udmh, mmh, hydrazine, chemistry, science

Id: AFLmqQ5ceS8

Length: 11min 34sec (694 seconds)

Published: Fri Nov 08 2019