Hi it's me Tim dad the everyday astronaut I'm here, at SpaceX, is brand new launch facility, in Boca Chica Texas, to, check out the, holy, grail, of rocket, engines and that SpaceX. Is upcoming, Raptor engine an engine like this has never actually been used on a rocket before now this is a methane, powered, full, flow stage, combustion, cycle engine, talking, about a rocket engines that's this complex, can be really intimidating, and in, order to put it into context, against other engines, and other engine cycles, we're gonna do a full comparison of the Raptor engine versus a bunch of other engines including, SpaceX's current workhorse the Merlin engine against, the rs.25. The Space Shuttle main engine the f1 engine that powered the Saturn 5 the, rd-180. And blue, Origins be4. That also runs on methane and as if the full flow of stage, combustion, cycle wasn't. Enough spacex, is also doing something else unique they're powering that thing with liquid, methane and that's something that's actually never been done on an orbital class rocket, so, we're gonna take a look at the characteristics, of methane and see, if we can figure out why, SpaceX, chose methane, instead. Of any other common propellant, now this engine isn't, really the best to anything, it's not the most powerful it's not the highest thrust to weight ratio of any engine it's not, even the most efficient, but it does a lot of things really. Really well. So by the end of this video hopefully, we have all the context to understand why the Raptor engine is special, how it compares to other rockets, why, it's using liquid methane and then, hopefully, we'll know if it really is the king of rocket engines let's, get started. Now. In case you didn't notice when you clicked on this video this, is a very, very. Long, video, sorry. Not, sorry but, if you're anything like me you, keep hearing a lot of hype about the Raptor engine and you want to appreciate it but you don't even know where to start well, I've spent quite a while really, studying up on the subject so I can lay down a good foundation in order to help us really truly fully appreciate, the Raptor engine well and, quite. Frankly all rocket. Engines and if you're anything like me maybe, you've stared at diagrams like this or, like this or, like this, one for hours until you feel like your head's going to explode so.
In Order to avoid that I've actually whipped up some really simple versions, of rocket engine cycles for all of us to enjoy which, will hopefully help, us grasp these crazy, concepts, but in case this isn't your first rodeo here's, the timestamps, if you want to jump to a certain section there's, also links in the description, to each section as well as an article version of this entire video at my website every, day astronaut, calm in case you want to study some of the numbers a little more in-depth or see, sources, of some of the material, now we're gonna start off with a super, quick physics, lesson but bear with me we're gonna dive in and get plenty of nitty gritty details okay so let's, start off with this rockets, are basically, just propellant. With some skin, around it to keep it in place and they, have a thing on the back that can throw said propellant, really. Really fast and to way oversimplify. It even more the, faster, you can throw, that propellant, the better now the easiest way to do this is by storing, all the propellant in your tanks under really high pressure then put, a valve on one end of the tank and a propelling, nozzle that accelerates, the propellant into workable. Thrust done. No. Crazy pumps, are complicated, systems just open, a valve and let er rip this. Is called a pressure fed rocket engine and there's a few main types cold, gas mono, prop and bipropellant pressure fed engines you'll often find these used in reaction, control systems because they're simple, reliable, and they react quickly but pressure fed engines have one big limiting, factor pressure, always, flows from high to low so, the engine can never. Be higher, pressure than the propellant, tanks in order to store propellant, under high pressure your, tanks will need to be strong, and therefore, thicker, and thicker and heavier and heavier look. At composite, overwrapped pressure, vessels or Co PVS they're, capable of storing gases, at almost, 10,000. Psi or. 700. Bar and despite this there's still a limited, amount of propellant and pressure they can store and this, does not scale, up very well when you're trying to deliver a payload to orbit so, smart rocket scientists quickly realized in order to make the rocket as lightweight as possible there's. Really only one, thing they, could do, increase. The enthalpy, that would, be a great, metal band name you're, welcome internet enthalpy, is basically, the relationship between volume pressure, and temperature. A higher. Pressure and temperature, inside the combustion chamber, equals, higher efficiency, and more, mass sub through the rocket engine equals, more thrust so in order to shove more propellant into the engine you could either increase, the pressure in the tanks or just, shoot the propellant into the combustion chamber what's a really high powered pump hmm. The second, option sounds, like a pretty good idea but, pumps moving hundreds, of liters of fuel per second, require a lot and boy. Do I mean a lot of energy to power them so, what if you took a tiny rocket, engine and aimed it right at a turbine, to, spin it up really, really fast you, can exchange some of the rocket propellants, chemical, energy for, kinetic, energy which, could then be used to spin these powerful, pumps welcome, to turbo pumps and stage combustion, cycle but. You've still got some limiting factors here like how high-pressure always wants to go to low pressure and how, he has, that habit, of melting, stuff, so. You've got to keep all these things in check while trying to squeeze every bit of power out of your engine now there's actually a lot of different variations of the cycles that we could talk about but I'm gonna stick with the three most common or, at least the three that matter the most when putting the Raptor into context, we have the gas generator cycle the, partial, flow stage combustion, cycle and lastly, we'll look at the full flow stage combustion, cycle and perhaps. In a future video I'll try and do a full rundown of all liquid, fueled rocket engines, including, fun new alternatives, like the, electric pump fed engines seen on rocket lab electron, rocket. So. Let's start with the gas generator cycle known as the open cycle this is probably one of the most common, types of liquid fueled rocket engine used on orbital, rockets it's definitely more complicated than a pressure fed system but it's fairly, simple, well. At least compared to their closed cycle counterparts. Now I'm gonna way way, oversimplify. This so it's as easy to grasp as humanly possible, in real, life there's literally dozens of, valves, a hive of wires and extra tiny little pipes everywhere helium.
To Back pressure the tanks fuel, flowing through the nozzle and the combustion chamber to cool it and there's, an ignition source for the pre burner and the combustion chamber, but again for the purpose, of making this as simple, and as digestible, as possible just know there's a lot, of stuff missing from these diagrams but, for now we're gonna focus on the flow of these engines so we can grasp that concept first. The gas generator cycle works, by pumping the fuel and oxidizer into, the combustion chamber using, a turbo pump the, turbo pump has a few main parts a mini, rocket engine called the free burner a turbine. Connected to a shaft, and then a pump or two that push propellant, into the combustion chamber now, you might hear the turbo pump assembly called the power pack because, it really, is what powers the engine in the open cycle system the spent propellant, from the pre burner is simply dumped overboard and does not contribute, any significant, thrust this, makes it less efficient, since the fuel and oxidizers, are used to spin the pumps is basically. Wasted, now the funny thing about a turbo pump is that it kind of has a chicken-and-egg, syndrome, situation, that makes it pretty difficult to, start up since the pre burner that, powers the turbo pump needs, high-pressure. Fuel and oxidizer, to operate. So the pre burner requires, the turbo pumps to spin, before, it can get up to full operational pressure, itself, but. The turbo pumps need the pre burner to fire in order to spin the turbo pumps but, the pre burner needs the turbo, pumps too yeah. You, can see where this is going this makes starting a gas generator pretty, tricky, there's a few ways to do this but we don't need to get into all that in this video that sounds like a fun topic for future videos though so back to the turbo pumps remember, pressure, always flows, from high to low so, the turbo pumps need to be a higher pressure than the chamber pressure and this, means the inlet slee to the pre burner is actually. The highest pressure point in the entire rocket engine everything. Else downstream. Is lower, pressure, but notice something here take. A look at SpaceX's merlin engine which runs on our p1 or rocket, propellant 1 and liquid, oxygen notice. How black, the smoke is coming out of the pre burner exhaust, why would it be so Sudi, compared, to the main combustion, chamber, which leaves almost no visible. Exhaust, well, that's because rocket, propellant can get super hot like. Thousands. And thousands, of degrees Celsius, so to make sure the temperature isn't so hot that it melts the turbine and the entire turbo pump assembly they, need to make sure it's cool enough to continually, operate, running. At the perfect fuel and oxidizer ratio is the most efficient, and releases the most energy, but, it also produces, a crazy, amount of heat so in order to keep the temperatures low you can run the pre burner at a less than optimal, ratio so either too much fuel known as fuel rich or too, much oxidizer, or oxygen, rich running, at our p1 engine fuel rich means you'll see some unburned, fuel appearing, as dark clouds of soot the, highly pressurized unburned, carbon molecules. Bond and form polymers, which, is a process, known as coking, this. Starts, to stick to everything, it touches and can block injectors. Or even. Do damage to the turbine itself so what if you didn't want to waste all that highly pressurized propellant, I mean after all since it's running cooler by being fuel rich doesn't.
That Mean there's a bunch, of unburned, fuel literally. Being wasted, what. If you could just pipe that hot exhaust, gas and put it into the combustion chamber huh. Welcome. To the closed cycle the, closed cycle or stage combustion cycle increases. Engine efficiency by, using what would normally be lost exhausts, and connects, it to the combustion chamber, to help increase pressure and also, increase efficiency, so let's take the merlin engine and try closing, the loop let's take the exhaust and just pipe it straight in the combustion chamber oh. No. We, just put a bunch of soot and clogged all the injectors, you, do. Not go to space today my friend but there's a few solutions to this problem so let's see how the Soviets, solved it the first operational. Close cycle engine they made was the NK, 15, designed for their n1. Rocket they later upgraded it to the NK 33, and then many versions from there stemmed out including the rd-180. Which, is what is used on the Atlas 5 today, since, the MK 15, + NK 33, runs on our p1 like the Merlin you can't run your pre-burners, fuel, rich because of the coking problem so, if you want to create a closed, cycle engine, with our p1 the, answer is running the pre burner oxygen-rich. Easy, as that right, well. Now you're blasting, superheated. Highly, pressurized gaseous. Oxygen, which, will turn just about anything into, soup right, at your precision-machined crazy, low, tolerance, turbine. Blade doing. So is actually considered, impossible, by the United States and they basically gave up on trying they. Didn't think a metal alloy existed. That could withstand these crazy, crazy, conditions. And they, didn't believe the Soviets, had made such an efficient and powerful rp1, powered engine until, after, the collapse of the Soviet Union and the, u.s. engineers got to see them and test them out firsthand but the Soviets had indeed, worked their butts off and they had made a special alloy that can magically, with, science, withstand. The crazy conditions, of an oxygen-rich, pre, burner with a closed cycle engine you don't just use some, fuel and some, oxidizer, and burn, that in the pre burner to spin the turbine you actually shoot all of, the rich propellant, through the turbine so with an oxygen rich cycle, all of the oxygen actually goes through the pre burner and just the, right amount of fuel goes to the pre burner you, only need enough to, give the turbine, the right amount of energy to spin the pumps fast enough to, get the right pressures for the pre burner and the combustion chamber, to make the right amount of power to shoot the thing into space it's, just crazy. So back, to this oxygen rich pre burner that now, hot, gaseous, oxygen is forced into the combustion chamber where, it meets liquid, fuel they, may end go boom and we get a nice clean and efficient burn without really, wasting, any propellant, but still like all engines, the chamber, pressure cannot, be higher than the pump pressure so. The pumps, actually, have a lot of weight on their tiny little metal shoulders, now if you're sitting there thinking that the United States just sat back and let the Soviets have all the closed-cycle glory you'd.
Be Wrong, it took the United it's a little bit longer but they eventually figured, out a closed cycle engine, but, it was very different from the oxygen-rich, cycle. The United States pursued a closed-loop cycle, but they went with a fuel, rich pre burner but. Wait we, just learned that fuel rich pre-burners, exhaust, is so, sooty that it pretty much ruins anything, right, well, sure if you're using rp1, or any other carbon, heavy fuel that's, definitely. Going to be the outcome so the United States went with a different, fuel. Hydrogen. Okay so now we've avoided the problem of blasting crazy hot high-pressure oxygen to anything dear and precious but. Now we've opened up a new can of worms hydrogen. Is significantly. Less dense than our p1 or liquid. Oxygen it's so, much less dense it takes a huge and really complex, turbo pump to flow the right amount of hydrogen into the combustion chamber, since our p1 and lox are relatively, similar in density, and in ratios, they, can be run on a single shaft using a single, pre burner because of this the engineers, at Rocketdyne pursued, an engine known as the rs.25. Which, would go on to power the space shuttle they, realized that because of the large difference between the pumps they, might as well have two different pre-burners, one, for the hydrogen pump and one for the oxygen pump so that's, what they did but having two separate shafts created, another, new problem now engineers, were putting high pressure hot gaseous, hydrogen on the, same shaft right. Next, door to the liquid oxygen pump, if some, of that hydrogen, would leak out of the pre burner it, would start a fire in the LOX pump which, is catastrophic. Ly, bad hydrogen, is also very, hard to contain because it's so not, dense. Undeads. Lightweight. It, likes to sneak through cracks and get out anywhere, at Ken so engineers, had to make an elaborate, seal to keep the hot hydrogen from sneaking out the seal required for this is called a purge seal and it's actually pressurized, by helium, so, that it's the highest point of pressure so if the seal leaks it just leaks inert, helium it's.
Genius But take a look at how different the LOX turbo pump and the hydrogen turbo, pump seals look you. Can tell how much more engineering time and effort had to go into the hydrogen, seals I mean, the people that think of this stuff are nuts. The rs.25, is still considered, to be about the best engine ever made with, a fairly high thrust-to-weight ratio, and unmatched, efficiency okay, now that we've talked all about the dual pre burner fuel rich rs.25, here's, a simplified, diagram of, that now, I didn't, bother making the fuel pumps different sizes and I just want to focus on the flow here and help make that as simple as possible but do note both. Pre-burners. Of the rs.25, run fuel-rich, so. Although, they might look the same they power different, pumps and I'll, just let this run here for a few seconds so you can study it for a bit but don't worry we'll also put all these up on screen at the same time once we cover them all so, the close cycle improves, the overall performance of the engine and is highly advantageous, so. How can it get any better than this we're, finally, ready to talk about the full flow stage combustion, cycle which, basically, just combines the two cycle, methods we just talked about with, the full flow stage combustion cycle you take two pre-burners, one, that runs fuel rich and one, that runs oxygen. Rich the fuel rich pre-burners, powers, the fuel pump and the oxygen, rich pre burner powers, the LOX pump this means the full flow stage combustion cycle needs to tackle the oxygen rich problems, which again, is solved. By developing, very, strong, metal alloys. So SpaceX develop their own super, alloys in-house, that they named SX, 500. According, to Elon Musk it's, capable of over 800. Bar of hot oxygen-rich, gas, that, may have been one of the biggest hurdles and developing the Raptor engine luckily, the fuel rich side only pumps, fuel so if some of that hot fuel leaks through the seal on the shaft it, just comes in contact with more fuel which, is kind of no big deal, so no need for one of those really really elaborate, seals full, flow likely, wouldn't work with our p1 due to the coking, problems with a fuel rich pre burner but, other fuels are still valid to use this design but, more, on that in a minute the advantage of the system is that since both the fuel and the oxidizer arrive in the combustion chamber as a hot gas, there's better combustion and hotter, temperatures, can be achieved there's also less of a need for that crazy sealing, system as we mentioned earlier and that's. Definitely, a good thing when you plan we use your engine over and over with little-to-no refurbishment, between flights and lastly because there's an inherent increase. In mass flow or how, quickly all the propellant, is shooting into the pre burner the, turbines, can run cooler and at, lower pressures, because the ratio of fuel and oxidizer needed. To spin the turbo pumps is much lower and think of it this way in an, open cycle you only want to use as little fuel and oxidizer as possible, in the pre-burners since it's all wasted and you, want it to be as hot as withstand, a ball to, make it more efficient, but with the full flow cycle all of the fuel and all of the oxidizer, goes through the pre-burners so, you can burn just exactly, as much propellant, as necessary, to power the turbo pumps but the cool thing is your fuel to oxidizer, ratios will be so crazy, fuel, rich and crazy. Oxygen, rich that the temperatures that the turbines will be much lower, and this, means longer lifespans, for the turbo pump assembly it also means more combustion, happens in the combustion, chamber and less, in the pre burner now here's the crazy part only, three engines, have demonstrated, the full flow stage combustion, cycle, ever.
In, The 60s the Soviets, developed an engine called the Rd 270. Which never, flew and in, the early 2000s. Aerojet, and Rocketdyne worked on an integrated, power head demonstrator, called wait, for it the integrated. Power head demonstrator, which, again, never made it past the test stand and the third attempt at developing a full flow stage combustion cycle engine is. SpaceX's. Raptor engine tada. That's, right the, Raptor engine is only the third attempt, at making this crazy type of engine it's, the first to ever do any type of work and leave a test, stand and fingers, crossed it'll be the first full flow stage combustion cycle engine, to reach orbit well. Actually just about anything this engine does will be a first this means SpaceX, had to tackle some crazy, crazy problems, I mean not only that same problem that plagues oxidizer. Rich cycles, like, having to have a really, really, strong metal alloy they, also have to learn how to control you, know two different, pre-burners, and two different cycles, to create the highest pressures. Of any chamber, pressure ever they, just beat the rd-180, s record of about 265. Bar when they 270. Bar and they're not even done they're hoping for 300. Bar inside. The combustion chamber, that's. Nuts and we'll talk more about that in a second but before we move on now that we've done a rundown on all these engine cycle types let's put them all up on screen and let them run for a bit so you can watch each one and compare them side-by-side I know for myself it helps a lot to see them all together on the same screen at the same time. Since. The Raptor engine can't run a fuel, rich pre burner using, our p1 you'd, think the next most logical choice would be hydrogen. Well, SpaceX, didn't opt for either our p1 or hydrogen. They went with liquid, methane, so now we finally, have another topic to touch on why, did SpaceX 2s liquid, methane for the Raptor engine what, are the qualities that make it advantageous, over hydrogen. Or our p1. Today. No liquid, methane or otherwise, known as methyl LOX engine has gone to orbit so, what qualities, does it have that make it desirable let's take a look at methane compared to our p1 and hydrogen. Let's put methane in between our p1 and hydrogen you'll, see why here really, quickly so let's start, off with perhaps the biggest factor when designing your first stage the, density, of the propellant having.
A Denser fuel means the tanks are smaller, and lighter for a given mass of fuel a smaller. Tank equals. A lighter rocket, so here's the density, of these three fuels measured, in grams per liter, in, other words how much does one litre of this stuff way or really. What's its mass starting. Off with our p1 one, liter is around eight hundred and thirteen grams our, p1 is 11, times more dense than hydrogen which is only 70. Grams per liter and methyl. Ox is right in the middle at 422. Grams per liter remember how airships, or Zeppelin's used to be filled with hydrogen to make them lighter, than air well. That's because hydrogen, is so much less dense than our atmosphere, it makes for an excellent albeit. Really, flammable, gas for a balloon I mean, we. All remember that Hindenburg, right it. Should also be noted that 813. Grams per liter is an average for our p1 but, SpaceX. Chills there are p1 in their Falcon 9 and Falcon Heavy for. About a 2 to 4 percent increase, in density but. Historically. Our p ones density, is right around that 813. Grams per liter so in the case of density methane is kind of right in the middle of the two others but, there's more to it than just density. We also need to take into consideration the, ratio, of how much fuel is burned compared, to how much oxidizer, is burned this is the oxidizer, to fuel ratio so. Here's where things get a little more interesting, and the tables turn just a little bit rocket. Engineers have to take into account the mass of the fuel and the corresponding, weight of the tanks so. They don't actually burn propellant, at the perfect stoichiometric combustion. Ratio, they, find the perfect happy medium that bounces, tank size with, thrust output and specific. Impulse let's look at the mass ratios for fuel and oxidizer that the engineers, have come up with so, for these numbers are p1 is burned at 2 seven grams of oxygen to, one gram of RP one hydrogen. Burns it six, grams of oxygen to one gram of hydrogen and, methane burns. At three point seven grams of oxygen to one gram of methane these numbers can now help offset a little the massive, difference in density, so, let's visualize this, to help make it easier to digest liquid. Oxygen is. 1141. Grams per liter it's, a little more dense than our p1 so burning, locks and our p1 at a two point seven to one ratio for, every liter of LOX you need a little over half a liter of our p1 next up let's do hydrogen, now with hydrogen being eleven times less, dense than our p1 you'd, think it'd need a tank that's 11, times bigger, but. Luckily, engineers. Have found that it pays to burn LOX and hydrogen, at a six to one ratio for a good compromise this means for each liter of LOX you'd need two point seven liters of hydrogen so. Your fuel tank needs to be approximately. Five times larger compared. To our p1 so, yeah that helps that's why when we look at a hydrogen powered, Delta four versus, an RP one powered Falcon nine you, can see the fuel tank is much smaller, than the LOX tank on the Falcon nine but, the Delta four is about, the opposite, the LOX tank is much, smaller, than its fuel tank so now let's take a look at methane and this one gets kind of interesting LOX, is 2.7.
Times More dense than liquid methane, but, the burn ratio is, 3.7, grams of oxygen to, one gram of methane, so, you need point seven three liters of methane for. Every liter of LOX in other words your fuel tank would need to be about, 40%. Bigger for methyl LOX than it would need to be for our p1 despite. Our p1 actually being almost twice, as dense and compared. To hydrogen its, fuel tank would be about 3.7, times, smaller, so the fuel to oxidizer, ratio helps make a methane, fuel tank a lot closer to an RP one tank than, it is to a hydrogen, tank, another, huge variable, if any rocket, engine is how efficient, it is this is measured in specific, impulse or ISP, but, you can think of it kind of like a fuel economy of a gas powered car so. A high, specific impulse would be similar, to a high mile per gallon or kilometre per liter best way to think of specific impulses, to imagine you had one kilogram, of, for. How many seconds. Can, the engine push with 9.8. Newton's of force the. Longer can sip on that fuel while still pushing that hard the, higher it's specific, impulse and therefore, the, more work it can do with the same amount of fuel so. Again kind of like it's fuel economy so the higher the specific impulse, the less fuel it takes to do the same amount of work which is a good, thing a fuel-efficient. Engine is extremely. Important, and now due to the molecular weight of each fuel and their energy released when burned there's a different, potential for how quickly the exhaust gas can be expelled out the nozzle, this, means each fuel has a different, theoretical, specific. Impulse in an ideal imperfect world an rp1 powered engine could achieve about, 370. Seconds, an ideal. Hydrogen, powered engine could get, 532. Seconds, and guess. What a methane powered engine is right in the middle with, 459, seconds, real-world, examples, of this though are much lower. With our p1 engines seeing around 350. Seconds, like the merlin 1d vacuum, around, 380, seconds, for a methane powered engine like the Raptor vacuum might be some day and about 465. Seconds, for a hydrogen powered engine like the rl10, b2, next. Let's talk about how hot, each fuel burns a fuel, that burns cooler, is easier, on the engine and potentially, makes for a longer lifespan our people one can burn up to three thousand six hundred seventy Kelvin, hydrogen. 3070. Kelvin and if, you haven't guessed it by now methane. Is again, between the two at three, thousand, five hundred fifty Kelvin, speaking, of thermal considerations, let's, look at the boiling point for each of these fuels or at what point does the liquid, fuel boil, off and turn into a gas since. All these fuels need to remain in their liquid state in order to stay dense the. Higher the temperature the easier, it is to store the fuel a higher boiling point also means less or even no insulation, on the tanks to keep the propellant, from boiling off and of course less, insulation means, lighter tanks, yay, our p1 has a very, high boiling point even. Higher than water at, 490. Kelvin, hydrogen. On the other hand is near, absolute, zero at, a crazy, cold, 20. Kelvin that's insanely. Cold and it takes serious consideration, to keep anything at that temperature and like. The Goldilocks it is methane, is between the two at 111, Kelvin, which, although that's still very cold and requires, thermal considerations, and at least boils off at a temperature similar, to locks so, there's, that and because it's so close to the temperature of locks the tanks can share a common dome which, makes the vehicle lighter, locks. And hydrogen's, temperatures vary so wildly that, locks will boil off hydrogen and the hydrogen will, freeze locks solid, now on to the exhaust what.
Are The byproducts, of combustion, with these engines rp1. Is really the only one of these three that really pollutes, with any unburnt, carbons being left in our atmosphere alongside. With some water vapor but hydrogen, only produces, water vapor and methane produces, some carbon dioxide and water vapor as well but an interesting note now believe it or not as far as greenhouse gases, go water, in the upper atmosphere can, be pretty, bad but, I'll be doing a video in the future all about how much rockets pollute talking about their air pollution also, their ocean, pollution and even space debris is a consideration, so, stand, by because I think that video is gonna be awesome, now one metric that we're just kind of going to gloss over really quick but and talk about it generally is the cost and these tend to vary considerably and, it's actually really hard to pin down the exact prices, reliably, so for. The considerations. Rp1 is basically just highly, refined jet fuel which, jet fuel is a highly refined kerosene which. Kerosene is a highly refined diesel so. It's safe to assume it's going to be more expensive than diesel hydrogen, is also relatively, expensive despite, being abundant, refining. It storing and transporting it can be hard but, methane on the other hand is basically the same thing as natural gas and can, be relatively, cheap now, when you're talking about buying literally, tons of fuel the fuel costs can add up quickly so although. The cost of fuel shouldn't factor in too much it. Certainly is a consideration, but, without hard data on this one I don't even want to put it on our chart so, instead, let's talk about the more important, aspect of the fuel that's. Manufacturing. It and here's, where we get into specifically. Why SpaceX, sees methane, as an important, or even. A necessary, part of the company's future, SpaceX, is ultimate, goals are to develop a system capable of taking, humans out to Mars and back over, and over the Martian atmosphere is, co2 rich, now combine that with water mining, from the surface and subsurface, water on Mars through, electrolysis, and the Sabatier process. The, Martian atmosphere can be made into methane fuel so, you don't have to take all the fuel you need to get home with you you can make it right there using, Mars as resources, this, is called in situ, resource utilization or, is, ru now, you might be thinking well. If there's water can't, you just make hydrogen on the surface of Mars for your fuel well, yes, but one of the biggest problems with hydrogen, and long-duration, missions, is the boiling point of hydrogen remember, it takes serious considerations. To maintain, hydrogen, in a liquid state and that's. Necessary, to be useful as a fuel so for SpaceX methane. Makes a lot of sense it's, fairly dense meaning the rocket sizes, are pretty reasonable it's, fairly efficient, it burns clean and makes, for a highly reusable engine. It burns relatively, cool helping, expand, the lifespan of an engine which again is good for usability it's, cheap and easy to produce and can. Be easily produced. On the surface of Mars. Okay. Yeah. We. Finally made it this far and now, that we have a strong, grasp of how different engine cycles operate, and the fuels they use we, can finally line them all up side-by-side and compare their metrics to help us appreciate where each engine sits so now we're going to line up each engine by their fuel type and their cycles, so let's start off with SpaceX's, open cycle Merlin edge and that powers their Falcon 9 and Falcon Heavy rockets NPO.
And Argo meshes oxygen-rich. Closed-cycle. Rd-180. That, we see power the Atlas 5 rocket and, rocket. Dines open cycle f1, that, powers a Saturn 5 which all three of these engines run on RP 1 then. We have SpaceX's. Full flow stage combustion cycle Raptor, engine that, will power the starship, and super heavy booster and then, we have blue origins close cycle oxygen-rich, methane, powered be4, engine that, will power their new Glen rocket and do Lay's upcoming, Vulcan rocket and then, we have Aerojet, Rocketdyne s, close cycle fuel. Rich rs.25. Engine that, powered the space shuttle and will power the upcoming SLS, rocket which, runs on hydrogen a few quick notes here, the Raptor and the b4 as of the making of this video are still in development so, the numbers we have here. Are either their current state of progress like, the Raptor which, is constantly, improving literally, every day and in the case of the b4, those are the target, goals for the engine which Blue Origin has yet to hit so, just, keep that in mind that these numbers are definitely subject. To change and now because of this don't forget to check in with the article, version attached in the description, of this video this, video will likely, date itself with some of these numbers and I can't update this video but. I can, update the website when, more info comes through so if you're, looking to use any of these numbers as a source, please. Please, PLEASE double check the website for any updates, another fun note quick is look at the rd-180, now don't, be confused, this is a single, engine it, just has two combustion. Chambers there's, only a single turbo, pump that splits, his power into two combustion, chambers the Soviet Union was able to solve the crazy hot oxygen-rich, closed-cycle. Problem, but, they were unable to solve combustion, instability of large engine, so, instead of one large combustion, chamber they made multiple small, ones so first up let's take a look at their total thrust output at sea level since, all these engines run at sea level that's probably a fair place to compare them let's, go from the least amount of thrust to the most for, fun the, merlin produces point 8 4 mega newtons of thrust the rs.25. Produces, 1 point 8 6 mega newtons the raptor currently is at 2 mega newtons the b4, is hoping to hit 2 point 4 mega newtons the rd-180. 3, point 8 3, mega Newtons and the, f1, is still the king out of these at six point seven 7, mega Newton's now there was an engine called the RT 170, which actually produced more thrust than the f1 but, since it barely flew, I figured it wasn't as relevant in this lineup I thought, it'd probably be a good idea to go with engines that have actually been used a lot, thrust, is great but, what's maybe just, as important when designing rocket is the thrust to weight ratio, or. How heavy the engine is compared. To how much thrust it produces, a higher, thrust, to weight ratio engine. Ultimately, means less dead weight the rocket needs to lug around let's, start from the lowest to highest here, the lowest is actually, the space shuttles rs.25. At seventy, three to one then, there's the rd-180. Which is 78 to one then, we have the b efore at around eighty to one button keep in mind we don't actually have a really good number on this so, there might be some wiggle room there then. The f1 is ninety four to one then, we have the raptor which is at about one hundred and seven to one for, now and lastly. The, merlin is actually, the leader here with an astonishing. 198. To one thrust to weight ratio, yeah. That, thing is a powerhouse, ok, thrust is great and all but who cares how powerful, an engine is if it's terribly, inefficient so. Next, up let's check out their specific, impulse which again, is measured, in seconds, so starting with the least efficient, engine which is the f1 engine at, 263. To 304. Seconds, then, the Merlin engine at 282. To, 311. Seconds. Then, we get the rd-180. At 311. Seconds, to 338. Seconds, and somewhere. In that same, ballpark is the B for which is around, 310. To, 340. Seconds, next. Up is the Raptor engine which is 330. Seconds to around 350. Seconds, and lastly. The King here by far, is the rs.25.
Which Is three hundred and sixty-six, to, four hundred and fifty-two seconds, Wow. Now. One of the factors that affect both the thrust, and specific, impulse is chamber, pressure now generally, the, higher the chamber pressure the, more thrust and potentially. More, efficient, the engine can be so. Higher, chamber, pressures let, an engine be smaller, for a given thrust level also, improving their thrust to weight ratio the baby here is actually the f1, which only had 70, bar and his chamber pressure now, I do need to pause here for a second and remind you that seventy, bar is still 70, times the atmospheric pressure or the same amount of pressure you'd experience at 700. Metres underwater. Yikes. Okay so even the lowest chamber, pressure is still mind-bogglingly. High so, next up is the Merlin engine at 97. Bar then, the b4 will be around, 135. Ish, bar then, the RS 25, which is 206. Bar then, the rd-180. Which has been considered the king of operational, engines at about. 257. Bar that is until the Raptor engine which is now kind, of online which, is considered the new king of chamber pressure at, 270. Bars currently, and they, hope to get that thing up to 300. Bar again. 300. Bars like being three, kilometers, deep in the ocean I can't. Even fathom. Okay. That's enough of the specs of these engines now. Let's look at their operational, considerations, starting, with their approximate, cost now, again and this can be kind of hard to nail down so. These are the best estimates, that I could come up with these, numbers do factor, in inflation to make them all in today's dollar though let's go with the most expensive, and work our way down to the least expensive, engineer the most expensive, engine in the lineup is the rs.25, which has a sticker price of over 50, million dollars, per engine, yikes. Then. We have the f1 which was about 30 million dollars per engine then, the rd-180, which is 25 million dollars engine then, the b4 which is around, 8 million dollars per engine and for the Raptor Elon, has mentioned he thinks he can produce the Raptor for cheaper, than or close, to the Merlin engine if they can remove a lot of the complexity, that, the current engine has so, for now we're, gonna say 2 million, dollars as a pretty decent, ballpark, then we have the Merlin engine which is less than a million I think ok well cost is one thing but another strong, consideration, for the cost of the engine is whether or not it's reusable and here, only the, rd-180. And the f1 were not reusable, or at, least never reused, which is different, than all these other engines, which, will all be reused multiple times, the, rs.25. Was reused over and over with the record being 19, flights out of a single engine well, well then again that's after a few months, of refurbishment the. Merlin is hoping to see up to 10 flights without major refurbishment we. Know a design, goal for the b4 is to be reused, up to 25 times and, I think the Raptor engine hopes to see up to 50, flights but, again, aspirations. Are one thing, we'll see how history treats these claims but one quick fun little story here is don't forget the Merlin engine which SpaceX currently uses on the Falcon 9 in Falcon Heavy Rockets are already. Fired a bunch of times before they even make it to the pad each, engine that is built goes, from Hawthorne, California to there test stand in McGregor Texas where does a full duration burn, then, those engines go back to California where, they're integrated, onto the octave web which is at the base of the vehicle then, they take the entire stage, and they take it back out to McGregor for, a full duration static, fire so it goes through the whole mission basically, again then. They ship it to the launch pad where does a short static fire and then it flies the mission so, it's already done like three, missions, in duration, of firing by the time it flies for the first time so I'm not entirely sure what the most times a single engine has done a full duration burn we, know that some of the cores were sat out on the pad and fired for a really really really long time multiple.
Times Over and over so I think they've probably done almost ten flight, full, duration burns, out of a single engine but. You know I have, no doubt they can probably do that if they say I mean they have more experience in this than anybody already, reusing. Engines without really refurbishing, them so. I'm gonna definitely take their word for it on the top of the price there's actually some things here that start to get really interesting when we started looking at these numbers the first is an interesting metric that Elon talked about once in a tweet in February of 2019, saying. They hope to make the Raptor get better at, their thrust $2, ratio, now this is a really interesting concept when you think about it who cares how much an engine costs if one big engine is cheaper than two smaller ones for the same thrust or vice versa so, let's actually take a look at the dollar to kill a Newton ratio of these engines starting, with the most expensive dollar 2 kilo Newton engine which is the rs.25, at a crazy twenty, six thousand, eight hundred eighty one dollars two kilonewtons, of thrust then. The rd-180. Which is six, thousand, five hundred twenty seven dollars to one kilonewton, followed, by the f1, at. 4431. Dollars. Per kilonewton, and then, we get to the b 4, which is. 3333. Dollars to one kilonewton, the merlin engine at, 1170. Dollars per kilonewton, and the raptor at around one thousand, dollars per kilonewton, but now we can go even another step further since we know their dollar two kilonewton, ratio but, we also know, their reusability. Potential. Now, we can predict their potential, cost per kilonewton, per flight, which. Changes, based on how reusable, these engines actually are so, for starters since the rd-180, and the f1 aren't reusable, their price stays the same but, for the rest of the engines if we take into account how many flights they have slash, will have now, we start to see the rs.25. Reusability, pay off and kind, of close the gap bringing, its potential, cost down to just one, thousand, four hundred fourteen, dollars per kilonewton, per flight, but, here's where things get crazy blue. Origins b4, has potential, to truly, be game-changing and around one hundred and thirty three dollars per kilonewton, over, twenty five flights which, could make it about as cheap to operate as the merlin at one hundred and seventeen, dollars per kilonewton, per flight but, if the raptor engine truly, lives up to its hype it, could bring this number all the way down to $20. Per kilonewton, per flight, now. That is absolutely, game-changing. Sir money, and reusability, is a 21st, century focus for space flight but whatever HAP - good old proven, reliability, for. This let's, first look at how many operational, flights each engine has had not at the moment of shooting this video the Raptor and b4 haven't seen any operational. Flights, although, the Raptor is starting to leave the test stand and is being used on test vehicles like the star hopper but, for now neither, engine has a real, flight record so let's look at the other engines, first we have the f1 engine which was used on 17, flights next. Up is the Merlin engine which is at 71, flights and catching up quickly to the rd-180, which is at 79, flights but the king out of these was the rs.25. Which saw a hundred, and thirty-five flights, now lastly, how about reliability. And service between, the number of flights and this number we, can get a pretty good sense of how truly, reliable an engine is this. Number is really hard to just pin down since some of the engines may have shut down early, but, the mission was still a success on, a few of these so yes. It take a few of these with a grain of salt again the b4, and Raptor engine haven't flown yet so those numbers are unavailable, then. We have this Space Shuttle main engine which is over. 99.5%. Reliable. But, that gets hard to define when an engine doesn't fully, shut down and, then we have the Merlin at 99.9. Percent reliable it, sure helps when you have 10 engines, on each flight of the vehicle and with, only one engine ever failing, early on in his career and despite. That that mission was still a success so, the. Merlin is a very. Reliable, engine, now to end this technically, the rd-180. And the f1 are 100%. Reliable, but, with the f1, never having shutdown at all in any flight it gets the bold here, and depending, on how you define success and, reliability, technically.
The Rd-180. Is only kind. Of 100, percent reliable because, it got really, lucky once one time it shut down six, seconds, early on an Atlas five mission in 2016. This was due to a faulty, valve but, the mission went on to be a success, because, of some pure luck with, the Centaur upper stage having, enough spare delta-v to, carry out the mission had, that Valve failed even a second, earlier that. Mission would, have failed. Man, seeing all these numbers and considerations. It makes you realize just how, many variables, go into designing, rocket I mean change any one little, thing and it can have this massive ripple, effect on the entire design and the, implementation, of the vehicle as a whole so let's go back over all of this now that we know all the cycles, the fuels the aspirations, of SpaceX to see if we can figure out why the Raptor, engine exists, and figure. Out if it's worth all the effort let's, look at space X's ultimate plan make, a rapidly. And fully reusable vehicle. Capable of sending humans to the Moon and Mars as, inexpensively. And routinely as possible, it's. Not exactly, your everyday goal for a rocket huh in order to be rapidly, and fully reusable the, engine, needs to run clean and require, low maintenance with simple, turbo, pump seals and low, prerunner temperatures, hmm. A methane. Fueled full flow staged combustion, cycle engine sounds, like a good fit for reliability. Redundancy and, scale of manufacturing, considerations, it makes sense to employ a lot of engines, in order to scale an engine down but maintain, a high output chamber. Pressure needs to be high hmm. Sounds. Like a methane, fueled full flow stage combustion cycle engine is a good fit for interplanetary trips, methane, makes the most sense because it's boiling point makes, it usable on long-duration trips, to Mars which, guess what you, can produce methane. On Mars so for interplanetary, trips, a methane. Fueled full flow stage combustion cycle engine sounds, like a good fit methane is fairly, dense meaning, the tank size remains reasonable, which again is good for interplanetary, trips not, needing to lug around a lot of deadweight, making.
A Methane, fueled full flow stage combustion, cycle a, pretty good fit, okay, so let's, bring this all back around, now is the. Raptor engine really, the king of rocket engines, well, rocket. Science, like all things is a complex, series of compromises is it, the most efficient, engine no. Is it, the most powerful, engine no, is, it the cheapest engine probably, not is it, the most reusable, engine maybe, but does it do everything really well yeah. It is truly a Goldilocks, engine, doing everything it needs to do very very well it is, the perfect fit for your interplanetary. Spaceship, and despite, its complexity, SpaceX, is developing this engine at a rapid, pace I mean, knowing how much tweaking, SpaceX, did to their Merlin engine over a decade we're, just at the infancy, of the Raptor engine it's only gonna get better from here on out which, is crazy. So, all in all the Raptor engine is the, king of this. Application. It's a fantastic, engine to fulfill SpaceX's, goals for their starship vehicle, would it be the king of other applications. Maybe. Maybe, not and all the that decision, for the rocket scientists, and engineers who, get to make all those crazy decisions, every single day so what do you think is it, worth all this hassle to develop such a crazy and complex engine is this. Just the beginning for the Raptor engine and most, importantly is the, Raptor engine really the king of rocket, engines let. Me know your thoughts in the comments below okay I know I say this every video but I honestly could, not have done this video without helping, my patreon, supporters they. Not only kept me sane for the past five months as I worked on this video but they also went over all the data with me they got gave me great feedback in suggestions in the edits of this video if. You want to help support what I do or provide, feedback in videos or help script in research or if you just want to hang out and talk space consider, joining our exclusive, discord channel and our exclusive subreddit, by becoming a patreon member by going to patreon.com, slash, everyday, astronaut thank. You guys seriously I couldn't have made this video without you and while you're online be sure and check out my web store seriously, I have really cool things like these f1, t-shirts, tons, of other shirts there's, lots of new merchandise popping, up in there all the time so check back often we have things like grid fitting out of coasters and hats and shirts and mugs and prints just, literally, tons of cool rocket stuff so if that's your type of thing be, sure and check out my web store every day astronaut comm slash shop and then click on the music tab if you want to check out any of the songs used in this video that's all music that I've written over the years you.
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2019-05-26