Why Next Generation Rockets are Using Methane

hello it's Scott Manley here and the big news in the world of rocket science is the United Launch Alliance have chosen the be4 engine for their Vulcan rocket they've rejected the AR one engine that was in development from Aerojet Rocketdyne and instead they've gone with a completely new fuel technology the methane oxygen cycle and they aren't the only people switching over to use methane and liquid oxygen because SpaceX has wrapped our engine also uses methane and you'll notice that I'm actually pronouncing at methane like Americans do because I guess I live here and I want to avoid confusing people but yet the be4 engine is a fuel and oxygen rich staged combustion cycle and it generates about 2.4 mega newtons of thrust the raptor is a more ambitious engine it has a much more complex fuel cycle instead of a single turbo pump setup they have two pre-burners one which is fuel rich in one which is oxygen rich and then there was mix in the main combustion chamber and the whole thing generates about 1.7 mega Newton solar thrust but it's supposedly higher efficiency because of this air fuel cycle now our p1 is what is currently used by SpaceX for their Falcon 9 and by ula for the Atlas 5 in fact at the our p1 or kerosene has a very long history as a rocket fuel if you go back to the earliest days the Atlas and the Thor they were both using kerosene and liquid oxygen the first stages of the Saturn one and the Saturn 5 those use RP 1 RP 1 is essentially of a specification for how to take regular jet fuel and kerosene and make it a very high-grade version that is suitable for rockets is obviously quite a detailed specification now the reason why RP 1 was used was that well the earliest Rockets used ethanol which was nice because it could be watered down and also you could really water it down and drink it but to get higher performance they wanted to use something that was better an arc one or kerosene came up as an obvious example since they had existing suppliers who could then be could make there's better quality version they didn't have existing suppliers for for methane for highly refined methane so they you know they used went with the jet fuel and then when they needed to go to even higher specific impulses they had hydrogen which offered a very clear advantage where as methane didn't so much so that's why they didn't do it in the past so why are they doing it no why does methane offer interesting advantages well okay so let's let's actually talk specifically methane is the simplest hydrocarbon it is a carbon atom with four hydrogen's around the outside RP one is actually a collection of a whole lot of different carbon molecules it's typically represented as a kind of you know mid the median type is twelve carbons with twenty-four hydrogen's along the side but you know it could be a single chain or it could actually be a branching chain it could have like ten carbons it could have fourteen carbons there's a whole range and mixture of molecules in this it's actually much easier to refine methane down to the very simple molecule so because of this when it's burned it has less partial your combustion products that can form into polymers so first of all that makes designing the engine a little easier because you're don't have to worry with coking happening in the wrong area setting down deposits of carbon which might gum up your engines or use your injectors or any other stuff secondly because it has all those hydrogen's it has more hydrogen but compared to other you know other more complex hydrocarbons so where the exhaust products tend to be lighter it produces twice as much water compared to carbon dioxide for a compared to other materials so therefore the exhaust products are lighter and that gives you a slightly higher specific impulse on the other hand it is actually slightly less energetic so the exhaust isn't as which means that yeah because the exhaust just isn't as hot the specific impulses lower but because the exhaust products are lighter it ends up getting an advantage and specific impulse but you know if you're reusing your engine having cooler combustion chambers temperatures can only be considered a win but I think the real win here is that you can pressurize the tanks using the same gas that the tanks are containing in liquid form this is called autogenous pressurization and as you're burning the fuel you can heat some of it up in the engine and pass that back in to keep the tank pressures up no in the Falcon 9 in the Atlas 5 what you do is use helium for this because helium is light but if you can eliminate that it eliminates like another extra piece of complexity so this saves complexity saves mass and yeah so that's an obvious up sight now there is a downside and the downside is that methane is about half as dense as our p1 as you're talking something like 800 kilograms per cubic meter for our p1 versus about 400 for for methane and that what you would immediately think well the tanks would have to be twice as big but you also have to remember that you're burning this in a fuel oxygen mixture and the oxidizer really is should be considered part of the average density so when you combine the fuel and the oxidizer requirements for each design it's actually only about a twenty to twenty percent advantage versus 50% advantage so yeah it's not as good but it's pretty good it's quite acceptable I guess 20% rather than see helium or sorry hydrogen which is really bad and with that's all great yes sure it is cryogenic but actually cryogenic turns out to be kind of advantageous because it means more coolant and you can use this or two James pressurization so you know the extra complexity turns out to be a win in the end there is an other side of this is the Elon Musk is obviously very interested in Mars and back in the 90s there was an idea called Mars direct this was championed by Robert Zubrin it was a plan for a human Mars mission and a big part of this was the instead of shipping all the fuel to leave Mars to Mars you would actually only ship up a small amount of hydrogen about eight tons and you would ship a fuel production plant do we take carbon dioxide from the Martian atmosphere and using the Sabatier process you'd combine this with the hydrogen and you would get methane and liquid oxygen so you could get about a hundred tons of propellant and oxidizer out off you know eight tons of hydrogen which was very nice it would be enough to get you back into space the idea of course was that you would send your spacecraft out to manufacture the fuel you years before and you would only then send the people along when you were a hundred percent sure that you had the fuel and oxidizer set up and ready to go this is actually the the mission profile that they use in the Martian if you remember but the whole fuel production on Mars thing is a distant future kind of thing the real advantages of methane are hearing now in terms of being burning cleaner being able to burn cooler and being able to get slightly higher performance out of the whole thing and that is why everybody is switching over to but I'm gonna say it's not the only they're not the only alternative that's being championed right now vector space systems has just got a patent for a pressure fed rocket engine that instead of using methane or rp1 it's gonna use propylene or propane that is essentially three carbon atoms with six hydrogen atoms on the side there's a double bond in one of the carbons there and that's interesting it's gonna burn hotter it's actually gonna burn even hotter than our p1 so it has more energy and that actually helps it get slightly better performance than the RP 1 because the chicke carbon chain is shorter there's less you know partial combustion products to deal with so again less chance of of this cooking going on but yes congratulations to Blue Origin and of course to Jeff Bezos the founder I mean it's a really cool to see a new company come in with a new technology and actually become part of this big establishment let's see yes congratulations to you all I hope to see the Vulcan flying in in the coming years I'm Scott Manley fly safe [Music] [Music] you [Music]

Channel: Scott Manley

Views: 536,664

Rating: 4.9428101 out of 5

Keywords: methane, rockets, kerosene, chemistry, rocket science, spacex, ula, raptor, blue origin

Id: 4pzgFHrLXmc

Length: 9min 34sec (574 seconds)

Published: Tue Oct 02 2018

Reddit Comments

[u/filanwizard]

availability and transportability as well. methane is the majority content of natural gas, It is probably easier to get purified Methane from NG/LNG than it is to get RP-1 grade kerosene from crude. And naturally the big one, You can make it on Mars or any other location you can get hydrogen and CO2.

I would imagine KSC has a gas pipeline(heat and cooking) just branch off some to 39A and have an on site purifier installed by someone like Praxair or other vendors. Boca Chica will have a nearby LNG plant, Now admittedly that LNG plant is more to fill ships for export to other countries but I am sure they would be more than happy to sell the gas to fuel BFRs.

SpaceX could probably even work out deals on the lease for the purification equipment such as the company supplying it get to keep the filtered off gases(Ethane, Propane, Butane to name a few) all have marketable values.

[u/Decronym]

Acronyms, initialisms, abbreviations, contractions, and other phrases which expand to something larger, that I've seen in this thread:

Fewer Letters	More Letters
BFB	Big Falcon Booster (see BFR)
BFR	Big Falcon Rocket (2018 rebiggened edition)
	Yes, the F stands for something else; no, you're not the first to notice
BFS	Big Falcon Spaceship (see BFR)
H2	Molecular hydrogen
	Second half of the year/month
Isp	Specific impulse (as discussed by Scott Manley, and detailed by David Mee on YouTube)
ISRU	In-Situ Resource Utilization
ITS	Interplanetary Transport System (2016 oversized edition) (see MCT)
	Integrated Truss Structure
KSC	Kennedy Space Center, Florida
LNG	Liquefied Natural Gas
MCT	Mars Colonial Transporter (see ITS)
NG	New Glenn, two/three-stage orbital vehicle by Blue Origin
	Natural Gas (as opposed to pure methane)
	Northrop Grumman, aerospace manufacturer
RP-1	Rocket Propellant 1 (enhanced kerosene)

Jargon	Definition
Raptor	Methane-fueled rocket engine under development by SpaceX, see ITS
Sabatier	Reaction between hydrogen and carbon dioxide at high temperature and pressure, with nickel as catalyst, yielding methane and water

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^{Decronym is a community product of r/SpaceX, implemented by request
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[u/Evibear]

I can’t watch the video rn. Can someone ELI5?