The Entire Soviet Rocket Engine Family Tree
Hi, it's me, Tim Dodd, the Everyday Astronaut. If you're anything like me, maybe you've heard all about different rocket engines that have come from the Soviet Union with very similar names. And you get really confused about which ones, which, and which engines go on, what rocket and which ones changed and evolved into something else. I mean, they all sound pretty much the exact same and changing just one small number can lead you on a completely different route. It's honestly really hard to keep track of. So today we're going to actually try and straighten out the confusing family tree of the Soviet rocket engines by drawing out what might be the most comprehensive chart of almost every single engine that has ever flown to orbit.
Now, although we'll really only be focusing on chemical rocket engines that were on rockets and not really even getting into spacecraft engines, we will be walking you through some incredible stories and fun anecdotes behind these engines because boy, oh boy, are there some crazy stories. After all, these are still some of the most powerful, the most advanced and downright ridiculous engine concepts that have ever been developed. So open wide, my friends you're about to be drinking from a fire hose of information. What took me over two years to learn and research. You're about to try and digest in just one sitting.
So get your notepads ready and hold on tight. Let's get started. Okay.
Right up front I just need to point out that we could only do this massive video thanks to my awesome supporters. If it weren't for the support of my Patrons and YouTube members, I wouldn't be pursuing such in-depth and hard to make videos. So if you like the work that you see in this video, maybe consider becoming a Patreon member at Patreon.com/everyday astronaut, or become a YouTube member by clicking down below, or maybe get yourself one of our awesome new, R-7 shirts that we made just for this video, as well as these awesome RD-171 shirts that after you watch this video, you'll probably think this is one of the coolest engines ever made. And best of all, we made posters of our incredible family tree. You can get all of this and more at everydayastronaut.com/shop. Okay.
Like always since this is a long, long video, here's the timestamps for each section. There's links in the description too. The YouTube play bar is broken up into these sections. And we have an article version of this video with sources and links as one mega reference for you everydayastronaut.com.
[ Soviet National Anthem]. There's a few notes and tricks that we need to talk about. That will be very helpful. No, I take, I take it back. Actually they're downright necessary. So in order to best understand this video, you might not want to skip this section, but do it at your own risk. First note, the aerospace community tends to say Russian engines.
And although that's actually mostly correct, as far as the origination of the physical units built, most engines we'll talk about are technically Soviet meaning former Soviet Union. By calling them Soviet engines where applicable it also helps give credit to the scientists and engineers from now former Soviet republics, who weren't Russian we'll be talking a lot about open cycle engines and closed cycle engines. As those of you who have watched my video about SpaceX's Raptor engine may know the difference between these two cycle types is what happens with the exhaust gas that spins the turbine that powers the propellant pumps. Open cycle engines simply dump the exhaust gases from the gas generator overboard, which is generally simpler, but less efficient close cycle or stage combustion cycle engines.
Don't really have a gas generator. Instead it's considered a preburner and runs either all of the fuel or all of the oxidizer through the turbine. And then it routes that now hot gas into the main combustion chamber.
So no propellant is wasted. On our chart, the border around each engine will tell you whether it's open cycle or closed. Open cycle engines, won't have a border around them while closed cycle engines will have a solid white border around them.
Another thing we're going to be talking about a lot is fuel types. Hypergolic propellants are those that will spontaneously combust when they come in contact with each other, which makes for a very simple and reliable ignition sequence. They're also, storable at room temperature for years and years, but are extremely toxic and corrosive. Meanwhile,
liquid oxygen or LOx based fuels often go by a shortened name. There's T-1 and RG-1 or in the U S we use RP-1, which are kerosene based fuels that are often called Kerolox. Then there's hydrogen or Hyrolox and there's methane or Methalox. But notice we said T-1 and RG-1 for Kerolox and not just RP-1.
This is a very important and fun little note. T-1 is similar to aircraft kerosene that's right. Some of these rockets pretty much just run on regular old jet fuels, similar to our Jet A that powers our airliners while newer rockets use RG-1, which is also called naphthyl.
The hardest part about LOx based propellant is keeping everything at working temperatures. So not having the cryogenic propellant warm-up and boil off before we need to use them. Our chart will show Kerolox engines in red alcohol engines in teal hydrolox in blue and hypergolic engines in some shade of orange or yellow, the shade of orange will vary depending on what exact combination of propellant they are. We'll talk about specific impulse, a decent amount, which is how efficient a rocket engine is. Specific impulse is abbreviated as ISP and is measured in seconds. The higher, the number,
the better kind of like the gas or fuel efficiency of a car. We'll be quoting engine specs in vacuum and or sea level if they were used at sea level. And with thrust measured in kilonewtons. You'll hear us talk about combustion instability quite a bit. In this video. The combustion chamber of a rocket engine is where the fuel and oxidizer get pumped in and meet at high pressures so they can combust and produce thrust. The larger you make the combustion chamber and the higher your thrust output is the harder it generally is to maintain stable combustion. You can have large pockets of sudden pressure changes, and those can completely destroy the engine.
Another thing you're going to hear me say a good amount is OKB. OKB stands for this. I'm not even going to try, which translates to experimental design bureau. Now these were state owned design bureaus, mostly dealing with weapons and jets and advanced military technology. Despite them being state owned, they were super competitive with each other and often had strong figureheads who were competing for projects against each other. Now for the naming, I just honestly really wish there was an easy set of rules with the naming convention that I could teach you, but there really isn't as much of an order as you might crave, but you will notice us mostly talking about RD series of engines and NK series of engines. RD literally translates to rocket engine.
And you'll see us talk about RD zero XXX series engines RD one XX and RD 2 XX engines quite a bit, but the names primarily stem from which OKB the engines come from. The majority of engines we're going to talk about came from, OKB. 456, home of legendary propulsion engineer Valentine Glushko.
OKB-456 engines will almost always be an RD One XX or an RD 2 XX. RD one XX are engines that use LOx as their oxidizer. So kerlox, metholox and hydrolox.
While RD 2 X X means the engines run on hypergolic propellants. Then there's OKB 154 led by Semyon Kosberg who developed RD zero XXX series engines. They tended to focus on upper stage engines or at least engines that primarily operated in a vacuum. But of course, that isn't always true. There are a few exceptions. We'll also talk about engines from, OKB 276 led by Nikolay Kuznetsov, which are NK XX series engines. Yes. N K are just his initials.
OKB-276 was primarily an aircraft engine manufacturer who wound up making some of the most advanced engines. So for example, it could be confusing that the NK 32 engine was a jet engine used on the TU 160 strategic bomber. And then the NK 33 is a rocket engine meant for a variant of the N1 moon rocket. OKB-1, the headquarters of the Soviet space program was led by chief engineer Sergei Korolev. You'll actually see very few engines come from, OKB-1 on our charts, but most of them are just RD XX engines, but then there's OKB-2 led by Aleksei Isaev who made some engines that are S5.XX,
But really mostly just made smaller missile engines that we won't be talking about. Next. We won't be talking about many of these at all, either, but there was OKB 165 led by Arkhip Lyulka. That was also primarily an aircraft engine manufacturer would also make a couple RD XX engines that were also meant for the N1, but these were advanced hydrolox engines. Lastly, there was OKB 586 led by Mikhail Yangel who developed RD 8XX engines that are often either steering engines or occasionally main engines.
We won't see it on the chart that often because the steering engines are usually accompanying main engines, but they were a pretty influential design bureau based in Ukraine. But at the end of the day, the naming schemes tend to follow internal technology, commonalities like injectors or turbines, and they might have no rhyme or reason on the outside or to the average person other than which design bureau made them. But I hope this helps to just kind of keep in the back of your head throughout this video, but just in case you want to make things 10 times more confusing, there's also a number or index for almost every engine called the GRAU index. For instance, the RD 268 has a ground number of 15D168, while the RD 270 has a GRAU of 8D420, but that's all just way too confusing.
So just scratch it from your memory because we're not going to use it in this video at all, but it is a fun, albeit confusing little fact. And lastly, we're going to be drawing lines between the engines on our chart. Following a white line with an arrow will mean you're going to the next evolution and, or there's a common link between the two engines, a greenish yellowish line just means it's literally the same rocket engine, but it's on our chart more than once because it's used on multiple rockets. In general, going from left to right is getting newer and newer with the oldest rocket engines on the left and the newest engines on the right, but it's not really exact overall. So just think of it kind of more generally. If the engine flew on an orbital rocket, you'll see the rocket name on top or underneath the engine or engines.
So a stack of engines would be their stages with the first stages on the bottom and the upper stages on the top. We've also put these rocket engines into their respective families in a gray box outline. Okay, these are the terms and tips you should be familiar with in order to make best sense of this already confusing topic that's going to ensue, trying to untangle the Soviet rocket engine family tree. Let's start off with a little important history lesson of early pre orbital rocket engines. Not only because there's some fascinating history here,
but it also sets the stage for some key players and it all stems from one important moment, WW II, coming to an end. After all most modern rocket technologies stem from WWII, with the Nazi designed V2, rocket. Rockets were a terrifying weapon, a way to deliver warheads vast distances in a real hurry, no need to fly planes over enemy territory. Rockets were quick, hard to detect and virtually impossible to shoot down. The A4 engine at the heart of the V2 rocket. Wasn't the first liquid fueled rocket engine developed, but it was certainly the first one to be reliable enough to become the heart of a formidable weapon and become the first system capable of reaching space by crossing the Karman line.
The Germans had solved one of liquid fueled rockets, biggest problems, combustion instability, the German solution to making an engine more powerful wasn't just to scale up the engine, but it was to take smaller injectors that they knew worked well and put multiples of them into a single main combustion chamber. The A4 wound up with 18 injector cups in this super weird basket head configuration. This is where it all started, and it's our first benchmark that we can compare other engines against.
It would accomplish 265 kilonewtons of thrust at sea level and 294 kilonewtons in a vacuum with just over 200 seconds of specific impulse at sea level and 239 seconds in a vacuum. Although these numbers, aren't impressive by today's standards. This was just the beginning. The engine was only running at 15 bar of pressure. The pumps of these engines were powered by a separate system, basically steam powered. They would run a hydrogen peroxide over a potassium permanganate catalyst to create high pressure steam, which would spin the turbine that would then power the pumps. So fast-forward to the end of WW II and the start of the Cold War and both the United States and the Soviet Union were working to outdo each other with more powerful and longer range missiles capable of delivering warheads to the enemy territories in a hurry.
The U S and the Soviet Union gathered thousands of former German, rocket scientists. Most of whom were members of the Nazi party to help develop their own rockets. In the United States, Werner Von Braun, a former German who the U S snatched up post-war helped lead this effort, but in the Soviet Union, it was Ukrainian born Sergei Korolev, who was tasked with leading the former German scientists Korolev and his team of Soviet and former German engineers and scientists went about reverse engineering, the V2 rocket, and the A4 engine that powered it and began basically rebuilding it. These engine remakes were dubbed the RD 100, and they were nearly a clone of the A4, at least externally. In fact, some of the parts were being machined in Germany, still from the old factories at the same time Korolev and propulsion engineer Valentine Glushko started making a modified version of the RD 100, that would have no German scientists direct involvement.
And it was using only Soviet fabricated parts. It was called the RD-101. The RD-101 would have very minor tweaks and take inspiration from some of Glushko's former works such as his RD-1. For a little bit of time, the RD 100 and the RD 101 were both studied tweaked and prodded and upgraded, but it was pretty quickly realized that the RD 101 path could be upgraded quicker. By the end of 1949, there would be an RD 102 and RD 103 upgrades that would see substantially shortened engine thrust frames, but they also did a few other tweaks allowing for a more concentrated ethyl alcohol fuel. But they did end up basically doubling the thrust output of the original A4 by reaching 500 kilonewtons of thrust in a vacuum.
So the RD 103 was pretty impressive. But it was still time to go bigger, better, and more powerful cause a war around this same time Korolev was given his own experimental bureau. OKB-1 known today as RSC Energia. This would be where the future of the Soviet space program would be developed.
The German scientists who were working in the Soviet Union were revisiting some old German research and began to play around with simple new chamber shapes and injector concepts based on some old tests and ideas up to this point, all of these engines we've talked about still had that weird basket head designed with 18 separate injector cups, but there was a design that was patented in Germany that was more of a showerhead design for the injector. Now they originally just wanted to test the injectors in a very simple cylindrical chamber instead of putting multiple injectors into a complex basket head, and then firing the whole engine. They built just this little test bed for the injector and made a new style of engine called Lilliput or the KS 50 that had pure copper walls that were only about one millimeter thick that could handle higher combustion chamber temperatures with greater thermal conductivity, making it easier to keep cooled. It wound up being one of the first engines capable of running on kerosene, which would potentially offer much greater performance with the negative side effect of much higher temperatures. It was the last engines that the German engineers got to work on directly. The lessons learned from the KS 50 Lilliput would come in handy when Glushko was trying to create a massive new engine with almost 1200 kilonewtons of thrust at sea level, about five times the thrust of the original A4, it was called the RD 110, and would have been used on a radical new R 3 rocket that would have lacked any exterior aerodynamic fins for stability.
And it was to rely on gimbling the engine to steer and control the rocket. The plan for the RD 110 was to have 18 injectors in that same basket head configuration each with about 70 kilonewtons of thrust in order to reach the intended thrust levels. But in order to develop 70 kilonewton injectors, they would put them in a, another experimental combustion chamber. They called the ED-140, which was kind of similar to the KS 50 as they tested the ED-140 the engine wound up being very reliable, capable of running continuously and had very consistent startups. When all of a sudden done the RD 110 never actually was even test fired, likely due to concerns over cooling, but the ED-140's DNA would see the light of day in another engine.
In fact, this combustion chamber is still at the heart of one of the most famous Soviet rockets ever. And it's still flying today. The Soyuz, which is part of the incredible R-7 family of rockets. [MUSIC]. Oh, the R-7 one of my favorites.
This is the first rocket to reach orbit. We have to start here since, well, it kind of all started here and there's been so many versions of this vehicle with so many different engines flown on just this one, rocket family. The R-7 originally had a simple goal, be able to carry a three ton warhead 8,000 kilometers, which yes, as you maybe could guess that makes it capable of hitting mainland United States from the Soviet Union. In order to accomplish this, the OKB-1 design bureau realized they would need to develop a more powerful engine Valentin Glushkoo was tasked with trying to scale up the ED-140 we had just talked about into a new design called the RD 105, but he ran into some problems. As usual when you're trying to increase thrust, scaling up the combustion chamber was leading to combustion instability. So what if you took one large chamber and split it up into four smaller chambers problem solved.
I want to explain real quick what exactly we mean by multiple chambers and why this isn't considered multiple engines. So instead of one large combustion chamber where you pump in your fuel and oxidizer, you could make four smaller combustion chambers that equal pretty much the same output. And these multiple chambers are all fed by a common turbo pump. And the turbo pump is really the heart of the engine. It's generally easier to scale up your turbo pump machinery than it is to scale up the main combustion chamber due to that combustion instability that we talked about earlier. So although this isn't necessarily more mass efficient to have multiple chambers over one big one, it can reduce complexity and combustion instability, but if you lose your turbo pump, the entire engine is a goner.
Now oddly Glushko made this realization while working on another engine. But we'll talk about that more in a second. You'll notice this concept of multiple combustion chambers is a staple of many Soviet era designs, and will be a reoccurring theme throughout this video. The engine they ended up developing was called the RD 107 and its twin sibling, the RD 108 and believe it or not, they're pretty much still in use today. The RD-107 and 108 are virtually identical. The only difference is the number of steering nozzles known as vernier engines.
The outer boosters with the RD-107s only have a pair of vernier engines while the center core with the RD 108 has four vernier engines. These engines first flew on May 15th, 1957 on the first R-7 rocket, which featured four strap-on boosters surrounding a single core, all running on Kerolox. This allowed for a really simple ignition process where all of the cores and all of the engines could be lit on the ground simultaneously. And it didn't require the complication of trying to start an engine mid flight.
But my favorite thing about the ignition process is that their solution to lighting all of the engines is basically to put some giant wooden matches up inside the combustion chambers. That's right, engineers stick giant wooden T-shaped structures up the nozzle into the main combustion chamber of all of the engines. So each of the 32 chambers get their own matchstick. That's 20 for the main nozzles and 12 for the vernier nozzles. On the tip of the giant matchstick.
There's a pair of pyrotechnics that only need one of them to light successfully. And once there's confirmation of all 32 pyros firing they'll then flow the propellents into the main combustion chamber for full ignition. And yes, they still use giant wooden matchsticks to light the engines today. The staging is relatively simple. Where all four boosters fall away simultaneously. And while they're falling away, a valve pops open in the liquid oxygen tank, which helps propel the tanks away from the core stage in a beautiful formation now known as the Korolev cross. Some notes on these engines,
the RD 107 and RD 108 have nearly the same performance figures with the RD 107 being slightly better optimized at sea level and the RD 108 being ever so slightly more efficient in a vacuum, which makes sense since it operates in a vacuum, more than the RD, 107. The RD-107 was the first to hit that magic number of 1000 kilonewtons of thrust. These are some pretty impressive numbers, huge improvements over the early RD 100 engines.
The turbo pump of the RD 107 and RD-108 is essentially powered by steam. Just like the A4. Yup, they still just run hydrogen peroxide over a catalyst, which creates high pressure searing hot gases that then spins the turbine, which powers the liquid oxygen pump and the kerosene pump.
This also means that there's a fully separate tank just to store the hydrogen peroxide, which although it's not mass efficient to require another tank to spin your pumps. It is a very simple and effective solution still in use today. Some cool innovations of this engine include those multiple combustion chambers variable mixture ratios, which helped each core drain its propellant equally. And it used regenerative cooling another innovation where those vernier engines for steering, which was a lot more elegant solution compared to the heavy graphite control veins that would help steer the original V2 engine by just diverting the flame. Since it was first flown in 1957, the RD 107 / 108 has gone through very little changes. There was the RD 117/118, which flew 786 times from 1973 to 2017 on the Soyuz U and U2.
They are very similar to the original, mostly having some small structural changes, different injectors, which offered minor performance increases and had parts of slightly varying origins compared to the RD 107 and 108. The RD 117 / 118 also sometimes ran on a fuel called synthin. It's a hydrocarbon based fuel, which offered increased performance, but the fuel is much more expensive. So it's just often not really considered worth it. Finally,
we see the RD 107A/108A, which would fly 70 times from 2001 through 2019 on the Soyuz FG. And they're also on the new Soyuz 2, which started flying in 2004 and is still flying. The RD 107A and 108A offered slightly higher thrust compared to the RD 107 and 108. Here's the 107 and the 107A side by side.
You can see the A's had a modest bump and thrust and a nice little bump in efficiency too. Here's an important note. If you're ever looking up info on these rockets, the common staging scheme tends to be that the side boosters are stage one, the core stage, which runs at the same time and is lit simultaneously to the side boosters is considered stage two. Then on top of that is stage three and sometimes there's even a 4th stage. In the U S we tend to say that the core stage of a rocket is stage one. And if there's boosters that also ignite with it at launch, they're either just simply called boosters or sometimes stage zero and not to be confused with how SpaceX calls their launch and landing pad at STARBASE stage zero, we'll be following the Soviet naming scheme in this video.
So that does it for the first stages of the R-7 rocket family. But in order to increase capacity, the R-7 needed an upper stage or a third stage. And the first upper stage they develop had a mighty task at hand, reach the moon. The Soviet Union began developing a missile called the 8K73 in 1957. For this Glushko developed an engine called the RD 109, which would increase its specific impulse to an impressive 334 seconds and produce 102 kilonewtons of thrust. It ran on LOx and unsymmetrical dimethyl hydrazine also known as UDMH, which is an interesting combo since it has the pains of both cryogenic liquid oxygen, plus the pains of the terribly toxic hydrazine, which Korolev just hated.
So it was scrapped and would never actually see flight. Instead. It would be reborn on a, another rocket that we'll talk about here in a second, the Vostok variant of the R-7 wound up being the first R-7 rocket to have a third stage called Blok E, which made it much more capable. The engine that made this possible was called the RD 0105, not to be confused with the RD 105, which was that failed attempt at the original R-7 main engine.
But the RD 0105 was based on the Vernier engines on the RD 107/108, and it also ran on Kerolox. Glushko passed the torch off to Kosberg to build the engine. It wound up developing 49 kilonewtons of thrust in space and hit 316 seconds of specific impulse. Meanwhile,
Glushko was busy upgrading the engine for an even more impressive upper stage for a version of Vostok called the Vostok K for this, he would take the RD 0105 and modify it to be the RD 0109. It also had a lower mass and increased reliability, thanks to its new lightweight combustion chamber. Now, these tweaks made it capable enough to put Yuri Gagarin into orbit on April 12th, 1961. It always wows me that the first human in space didn't just do some suborbital 20 minute flight, but instead he actually went full blown orbital. The United States didn't accomplish this feat until John Glenn's flight on Mercury / Atlas 6 onboard Friendship 7 on February 20th, 1962.
A fun note about these upper stage engines is they start their ignition sequence while they're still attached to the core stage. Now this is called hot fire staging, and boy, is it wild? Have you ever noticed that graded fence looking section of the R-7 rocket that's the interstage and it's open like that so they can start the engine while the two stages are still connected. This makes it so they didn't have to utilize any other ullage motor or a secondary motor to accelerate the upper stage to settle the propellents on the bottom of the tanks before turning on the engine, which you need to do to avoid sucking up gas bubbles, and having rough starts you'll notice that truss work interstage on other Soviet rockets. It was a simple solution to a tricky problem. So keep your eyes open for that as we continue this video, but you may also know that the United States did hot fire staging of their Titan rockets as well.
So from here on out the third stage of the R-7 got modest updates or changes, and each time it did, it basically became a different engine with different numbers. So just in case you're not confused yet. Here's one that baffles me after the RD 0105 and RD 0109. There was an RD 0106, which was a 4 chamber version and offered over four times the thrust. This was used on the Blok I third stage for an R-7 variant called the Molynia rocket that flew for the first time in 1960. The RD 0106 would then be tweaked a little to become the RD 0107 and then the RD 0108, which would fly 300 times on the Voskhod R-7 from 1963 to 1976. And then the RD 0110,
which saw its first flight in 1965. And it's, what's still being used today on the Soyuz 2.1 A that currently flies humans. So I wish I could say this was the final version of the third stage engine for the R-7 family because no, it's, it's, it's not, there's also the RD 0124, which is a pretty fancy closed cycle engine intended to be used universally amongst several vehicles. It doesn't have any vernier engines and it uses RG 1 a first for the sole use instead of the usual T1 kerosene. Because it's closed cycle,
its specific impulse is increased from 326 seconds to 359 seconds and is used for larger or higher energy payloads. It first started flying in 2006 and is still in use today on the Soyuz 2.1 B. So that about does it for the third stage of the R-7. However, it even ended up growing a 4th stage and it would actually do that before Yuri made his famous flight. A fourth stage was flown way back in 1960 on that Molniya rocket. So it was actually on a really early variant of the R-7 that would fly 40 times over all with a 50% success rate, but coolest of all, it was high enough performance for interplanetary missions. And here ladies and gentlemen is where the Soviet Union did something that the U S engineers literally thought was impossible until they got their hands on Soviet rocket engines in the 90s. Already in 1958,
they began developing a closed cycle oxygen rich engine called the S1.5400. It may have initially only had 64 kilonewtons of thrust in a vacuum, but it achieved an impressive 338 seconds of specific impulse. It was way ahead of its time for a Kerolox engine, and it would fly successfully already in 1961 on an interplanetary mission to Venus. That was the very interplanetary probe.
The real breakthrough was developing metals, such as titanium alloys that could withstand having searing hot gaseous oxygen blasting at them without just turning them into soup. This trend would continue and the Soviet Union made it look really easy. Now I remember this one, the S1.5400, because it kind of became the basis of a ton of upcoming engines for other rockets, despite having very limited presence on the R-7 family, having only flown four times in total, the Soyuz U was the next R-7 to have a 4th stage that was powered by the S5.92 on the upper stage known as fregat, which first flew in 1973.
This is a small open cycle hypergolic fueled engine producing 19.6 kilonewtons of thrust with 327 seconds in a vacuum. One of its cool features is the ability to light 50 times in space with up to 300 days between ignitions. Now, wouldn't it just be fantastic if I could say this was it for the R-7 variants, but there's one bastard child in the set and it's missing all of its boosters. Now we'll get to that rocket and that engine in a second. But for now we're going to go into confusion town as if it wasn't confusing already. So hold onto your butts.
[ MUSIC]. While the R-7 is easily. One of the most notable rockets and was on its way to fulfill many important tasks. The Soviet Union wanted more options. Although the R-7 had plenty of performance because it used Kerolox.
It had a relatively narrow window of operation. Once it was fueled up, this is far from ideal for something that may need to deliver a warhead at quite literally the push of a button working with storable propellants is something that Glushko actually preferred. In fact, when he was having problems scaling up the RD 105, he was also working on engines that would run on nitric acid for the oxidizer instead of liquid oxygen. Like we had mentioned with the RD 109 he'd even started playing around with nitric acid and kerosene fueled aircraft engines in the 1940s. Now scaling up a rocket engine is hard, but nitric acid is even more difficult to get stable combustion running. So Glushko's solution wasn't to try to scale up the engine, but it was to actually scale down the combustion chamber and then create multiple nozzles.
Now he did this while working on an engine called the RD 211, ding, ding, ding. We have finally connected some dots here. My friends, this little bit of history is what sparked the Soviet's love for multi chambered engines. Like we already discussed with the RD 107. So now Glushko was working on this RD 200 series of engines, which would first see use on rockets called the R 12 and the R 14. These medium range ballistic missiles were led by chief designer, Mikhail Yangel from OKB 586 in Ukraine.
And were a major leap in range for missiles. The R 12, our rockets, you may be familiar with if you've ever heard of the Cuban missile crisis. Yes, the R 12s were deployed to Cuba where they could hit mainland United States. The R 12 featured a spinoff of the RD, 107 called the RD 2 14. It still featured a hydrogen peroxide gas generator, but it ran on nitric acid and kerosene, but that's not all Yangel would be working on. In fact,
he had a lot of his sleeves, a whole family of rockets. In fact, the next one would be a bigger brother to the R 12, the R 14. So he took the R-12's RD 214 first stage engine and upgraded it split up the four chambers into a pair of dual chambered engines called the RD 215. This upgraded RD 215 would fly in pairs, which would together be called the RD 216. So yes, that's correct. The RD 216 is literally just two dual chambered RD 215s that, yeah, this stuff just gets so confusing, but these little rockets would actually go on to become the second orbital rocket family to come from the Soviet Union. In fact,
the R 12 was actually studied to become the basis for an orbital launch vehicle as early as 1956. That's right. The Kosmos launchers were based on the R 12 and R 14, but featured a second stage on top of it with an engine called the RD 119. Remember when Glushko was working on the third stage for the R-7 and Korolev didn't want to use hydrazine well, here's where that work went, but there was a problem. The R 12 was a small rocket. So in order to make it an orbital launch vehicle, it'd need a very efficient second stage engine and the RD 109, although decent wouldn't cut it.
Glushko started tweaking the RD 109 and wound up putting a much larger expansion ratio nozzle on it to help it be more efficient in space in order to reach a higher specific impulse. They also did something pretty cool instead of gimbaling the engine or using vernier engines, it just took the exhaust from the gas generator and sent it out through four fixed pipes. Then an electronically driven gas distribution system would change how much exhausts would be flowing through each of these pipes in order to give it steering control. The exhaust from the gas generator was decomposed fuel, not oxidizer like most other Soviet engines tended to use at the time, such as hydrogen peroxide. These tweaks help them get the RD 119 to reach an impressive 352 seconds specific impulse, the Kosmos 1, 2, 3 3m, and a special variant called the K 65M- RB5 would go on to launch 625 times with about a 90% success rate. Overall, that's crazy that a rocket, I didn't even know existed, flew so much and pretty successfully at that.
Seeing the success of the R 12 and R 14, it was time to develop a more capable rocket one that could be used as a powerful Intercontinental ballistic missile, and be a more rapidly launchable counterpart to the R-7. The rocket Yangel developed for this task was the R 16. And let me tell you, there's a whole heck of a story here that we don't have time to go into with this video. Have you ever heard of the Nedelin catastrophe? If you haven't heard of it, maybe consider yourself lucky because the stories that come out of it are so gruesome, a part of me wishes I had never heard about it. Long story short, the first attempt of launching this rocket left at least 90 people, dead, dying, horrific and violent deaths. In an ironic twist. Perhaps one of the few times in history, smoking a cigarette actually saved someone's life.
And it happened to be chief designer Yangel who left the launchpad to go smokes and smoking next to a fully fueled Brocket was prohibited. Okay. But back to the rocket powering, the first stage of the R 16 was an engine called the RD 218, which was actually just three dual chambered RD 217s that were upgraded RD 215s. These engines had fixed nozzles. So the RD 218 was accompanied by a 4 chambered steering engine called the RD 68, much like the vernier engines on the RD, 107 / 108. Then there was a second stage on the R 16 that featured an engine called the RD 219, which was a derivative of the RD 217s in the RD 218, but slightly more optimized for vacuum and had its own quad chambered steering engine called the RD 69. After the roughest start ever to the program and several replacement workers and managers, for those who were lost in the Nedelin disaster, the R 16 went on to prove to be a formidable enough weapon, to see Yangel, be tasked with designing an even bigger rocket.
This would be the R 36 for this rocket. They would opt for a less corrosive alternative for a storable oxidizer swapping out the nitric acid based oxidizer for nitrogen tetroxide, along with unsymmetrical dimethyl hydrazine, which would become a staple of hypergolic rockets. Now this combination is also called N204 / UDMH.
The engines that they developed would be an upgraded and evolved version of the RD 218. This engine would be called the RD 251 and similar to the RD 218. It was made up of a cluster of three dual nozzled RD 250s.
On the second stage of the R 36, there was a vacuum optimized version called the RD 252. I love the RD 252 because even its gas generator exhaust pipe is optimized for vacuum operation. It was a healthy upgrade over its predecessor, the RD 219 and achieved 26 seconds better specific impulse, despite being relatively the same mass, the R 36 would become the basis for a space launch vehicle called the Tsyklon. It would evolve into one of the most reliable rockets ever made. The Tsyklon, Tsyklon 2, which was a two-stage rocket that made 106 flights with only two failures between 1969 and 2006.
There was also a three-stage version called the Tsyklon 3. The third stage had a small hypergolic open cycle engine called the RD 861, which had a single combustion chamber with four Vernier nozzles that were fed from the gas generator exhaust. The Tsyklon three also featured an upgraded RD, 251 called the RD 261 / 262. They changed it to be able to handle a wider range of operating temperatures since it would only be used as a space launch rocket and would always be launched from a pad instead of a missile silo. There was actually an R-36 orbital launcher that was still a silo-based launcher meant to launch nukes into orbit. Spooky.
The Tsyklon 3 halted production in 1991 with the collapse of the Soviet Union, but was still flown until 2009. There'd be some interesting politics involved with a Tsyklon 4 and Ukraine is still in pursuit of a Zenit rocket based Tsyklon 4M, but it has yet to fly. And some of these leftover RD 250 based engines would wind up in the hands of North Korea and Iran today, which has led to tensions between the United States, Ukraine and Russia. The R 36 is actually known by another name, the Dnepr, and this is the missile that Elon Musk tried to purchase from Russia when he wanted to send something off to Mars. And the Russians actually laughed him out of the room when he tried to buy it.
And that kind of led to the start of SpaceX in the long run, maybe they should have just sold him that one missile. In the 1960s Yangel and Chelomey started working on new projects that are aimed at further development of their ballistic missile program, Yangel proposed and new version, the R 36 M. As a result in 1969, the R 36 M project was approved. The first stage of the R 36 M rocket would use for single chambered RD 263 engines, which formed one RD 264 engine.
These were oxidizer rich closed cycle engines with impressive performance Yangel had been partnered up with OKB 456 for most of his propulsion needs up to this point, but then he ended up reaching out to OKB-154 feeling like OKB-456 was currently overworked on other projects. These engines ran on N204/UDMH, had a total thrust of 4,158 kilonewtons at sea level and 4,511 kilonewtons in vacuum had an ISP of 293 seconds at sea level and 318 seconds in a vacuum. A fun note about these engines is they had pretty large combustion chambers. In fact, so large, they were actually experiencing those problems with combustion instability and the flame getting crazy around the injector face.
So guess what they did? Nope. They didn't split it up into multiple combustion chambers for once they did what the U S did divide the injector face, using dividers. Since the R 36 M is a ballistic missile, let's not even talk about the rest of it, but keep that RD 264 in mind, since we'll see its heritage up down the road. The RD 200 series proved hypergolic fuels to be useful. And like we mentioned, Glushko preferred developing engines that ran on hypergolics.
This knowledge would sure come in handy for the next family of rockets. One of the most successful rockets to come from the Soviet Union, the Proton Korolev's R-7 rockets were doing quite well and Yangel was doing big things with his ICBM's, but there were other design bureaus looking to get funding for their designs. Chief designer of the OKB 52 design bureau, Vladimir Chelomey had his own plans for a modular rocket. Chelomey was developing the universal rocket family, otherwise known as the U R series. Initially, this was supposed to be a UR100, UR 200, UR 500, UR 700 and even the UR 900, which would have been powerful enough for a direct ascent moon mission. Chelomey, turned to Glushko who of course turned to hypergolic fuels.
It was also easy to sell a rocket concept as an ICBM when it used hypergolic fuels. Chelomey's idea was to have a large number of relatively cheap UR 100 missiles that had simple designs. Mr - UR-100 and the UR 100 N were approved and were being developed, but on a competitive basis against the R 36 M. For the MR UR 100, he was able to get fast-tracked and RD 268 engine, which was an improved version of the RD 264's RD 263 from the R 36 M and would actually be developed in parallel to it. But it wound up being higher performance. And for some reason,
it wasn't plagued with those same combustion instability problems at the injector face, which required those dividers, but they ended up keeping the dividers inside the combustion chamber anyway, just in case. They had a thrust of 1,149 kilonewtons at sea level and 1,239 kilonewtons in vacuum had an ISP of 296 seconds at sea level and 319 seconds in vacuum. The main difference between these two engines was the.
RD 268 engine was fixed while the RD 263 engines could gimbal seven degrees. But that's not all Chelomey was working on. He was also developing a larger UR 200 rocket. So he turned to design bureau OKB-154 to develop a high performance close cycle hypergolic engine kind of blending the S1.5400 and the RD 250 that we had talked about earlier.
The engine they built was called the RD 0202, and they were hoping this would be the engine to use across the entire lineup of his universal rockets. The RD 0202 was actually a module composed of three RD 0203's' and one RD 0204, which included a heat exchanger to pressurize the fuel tanks for the first stage. So, yes, let me repeat that, cause this is just one of the hardest things with some of these engines, the RD 0202 defies, all naming scheme logic. It has a zero first, which typically means it's an upper stage engine, but Nope, this is a sea level fired engine and the RD 0202 is actually just three RD 0203s and one RD 020 4.
Yep. Uh, good luck remembering that one, but they also built a vacuum optimized version called the RD 0205, which was a single RD 0206, based on the RD 0204 with an auxiliary vernier steering engine, the RD 0207. Are you getting more confused or less confused at this point? Because I have no idea. The U R 200 only saw a few test launches, but its work wouldn't go unused the RD 0205 would wind up on the second stage of Chelomey's next, even bigger rocket, the UR 500, which was originally designed to be an Intercontinental ballistic missile capable of delivering 50 to 100 megaton warheads. Well, it turns out the rocket wouldn't really see any light of day as an ICBM and instead would become a space launch vehicle, also known as the Proton, but Chelomey and Glushko would soon realize they needed a more powerful closed cycle engine for the UR 500 rocket because it wasn't going to make sense to use the RD 0202 on the first stage. The engine they developed was the RD 253, which was a huge leap forward in performance, reaching a record setting 147 bar in its main combustion chamber.
This leads to a high thrust level of 1,470 kilonewtons at sea level and 1,630 kilonewtons in vacuum and an impressive 285 seconds of specific impulse at sea level and 316 seconds in a vacuum that also has an extremely high thrust to weight ratio all around. It's an awesome engine fun fact, the RD 253 started development while the RD 250 was on the test stand right next to it. OKB 456 in 1964. They would take lessons learned from the troubled RD 250 to make the RD 2 3, getting it certified in a hurry.
It would quickly become a solid work horse. The RD 253 first successfully flew on the very first Proton rocket on July 16th, 1965. And it continued flying as either an upgraded RD 253F or RD 255 for a total of 314 times until its last launch on a Proton K in 2012 in 1965, the first Proton to fly an upgraded engine called the.
RD 275 would see flight. They increased the chamber pressure to an impressive 157 bar, which in turn raised its sea level thrust to 1,590 kilonewtons with its efficiency going up to 287 seconds at sea level and 316 seconds in a vacuum. But in 2007, one more upgrade to the RD 275 would be made called the RD 275M also known as the RD 276 for some reason, which would first see action on the maiden flight of the Proton M and again, featured higher chamber pressure. Now up to 165 bar allowing it to hit even higher thrust and a little bit better specific impulse to a fun little note about the Proton rocket, despite looking like it's a cluster of booster engines attached to a core stage. Those are not detachable boosters.
The reason it's shaped like that is because of its size constraints of getting segments of the rocket to the pad by rail. This definitely threw me for a loop when I first learned it. So the outer tanks are the UMDH tanks and the central tank is the N204 oxidizer tank. This allows all engines to be connected directly to the fuel and oxidizer tanks. So they have no need for a large down comer pipe through one of the tanks. It's actually pretty cool.
The second stage of the Proton originally was going to use a vacuum optimized version of the RD 0203/4 called the RD 0208/9. But as they continue to develop and grow the UR 500, they ended up upgrading the thrust and burn times, creating a set of engines called the RD 0210/0211. Similar to the other clusters of engines. There'd be three RD 0210s and one RD 0211 with the heat exchanger. But of course, for whatever reason,
they didn't just give it its own name, like all of the other ones. Instead, they just kind of called it the RD 2010. And you're just supposed to know what that means. Then there's a third stage, which would feature an upgraded version of the RD 0205, that was developed called the RD 0212, which was an RD 0213 main engine and four RD 0214 vernier steering engines. But the Proton did something kind of weird considering the whole thing runs on hypergolic propellants except for the fourth stage in the Proton K and M, which believe it or not ran on Kerolox.
This is unusual because normally the first stages are LOx based since liquid oxygen boils off so easily. And then upper stages are the ones that are hypergolic since they can be stored for so long without worrying about boiling off. But this is quite the opposite. Despite the boil off issues, the Blok D as it's called, has done 24 hour long missions.
The engine that powers the fourth stage is the RD 58 and it's a direct descendant of the S1.5400. It was originally developed to be the final stage of the N1 moon rocket. That we'll talk about more here in a second, but it actually would fly first on the Proton in 1967. There's an upgraded version called the RD 58M which offers a little better specific impulse for the Proton Blok D there's also a special version of that engine that has a carbon carbon nozzle extension.
There's also an RD 58MF upgrade that hasn't flown yet, and we don't really have good specs on it. So we'll just leave it off of our chart to be safe. But then there's also the Briz M, and the Briz K fourth stages, which were hypergolic, but didn't fly until 1999. These are powered by an engine called the S5.98m,
Which is a gas generator hypergolic engine producing just 19.6 kilonewtons of thrust. And it's a sibling to the S5.92 on the Fregat, but there's one last engine that Glushko and Chelomey would work on for the UR 700 and the UR 900 mega rockets that they were originally trying to push instead of the N1 and it's way too cool to not talk about, remember how Yangel ended up turning to OKB-154 to work on the RD 263, because he felt like Glushko was too busy at the moment. Well, there was good reason for him to be busy. He was working on perhaps the most epic engine ever made in 1962. The development of the RD 270 began.
Now what's awesome about the RD 270 is it was the holy grail of combustion cycles. The full flow stage combustion cycle, much like SpaceX is Raptor engine. They took a lot of lessons from the RD, 264 and RD 253 to make the RD 270 and boy, was it a masterpiece including how to scale up large combustion chambers and not be plagued by combustion instability. This would be the most powerful single chamber engine, the Soviet Union ever built and would come darn close to the thrust output of the F1 engines that the US built for the Saturn V. It reached a mind-boggling 6,272 kilonewtons at level and 6,713 kN in a vacuum with a very impressive 301 seconds at sea level and 322 seconds of specific impulse in a vacuum.
This is much better specific impulse than the F1, which only achieved 263 seconds of specific impulse at sea level and 304 seconds in a vacuum. Although the F1 was a good 15% more powerful at 6,770 kilonewtons at sea level and 7,700 kilonewtons in a vacuum. They test fired it 27 times with one engine, even seeing three fully successful full duration fires between 1967 and 1969. Oh, and just to add insult to injury, they even ran the RD 270M version on pentaborane, which was 15% more efficient. This would have made it probably the ultimate engine likely still today and would have been just so close to the thrust output of the F1 with much higher efficiency. Unfortunately,
the engine was canceled alongside the UR 701. The N1 was chosen as a Soviet moon rocket. So we keep tossing around the N1 and talking about it here and there. But I think now it's time, we actually dive into the awesome engines that powered the most powerful and downright crazy rocket to ever fly well for now Getting humans to the moon and home requires an awful lot of rocket.
Of course, the United States developed for the Saturn V, but meanwhile, Korolev had actually succeeded in pursuing his own mega rocket. The N1, as we mentioned before, he was in competition with Chelomey to get funding for his moon. Rocket after Chelomey is UR 700 and the UR 900 proposal got shot down. And with Korolev having sworn off the use of hypergolic altogether for the majority of the rocket, he had to find a powerful Kerolox based engine capable of lifting the massive N1. Since propulsion engineer Glushko had already buddied up with Chelomey for the RD 200 series hypergolic engines, Korolev turned to an aircraft engine design bureau, OKB 276, which was headed by Nikolai Dmitriyevich Kuznetsov. Korolev and Kuznetsov set out to design the Soviet Union's most powerful Kerolox engine knowing he'd need an awful lot of power to lift a rocket that would weigh almost 3 million kilograms.
The first engine they'd build was called the NK 9. It was an oxygen rich close cycle engine, and it became the basis for an upgraded engine called the NK 15, that would achieve the thrust numbers necessary for the massive 17 meter wide first stage booster called Blok A. Blok A would feature a whopping 30 NK 15s with 24 engines around the outer perimeter and six more on an inner ring sounds kind of like SpaceX's SuperHeavy, doesn't it at 1,526 kilonewtons of thrust each, they would offer a total of 45 mega Newtons of thrust. So 45 million Newtons, yes, that's almost 30% more thrust than the Saturn Vs first stage which had 35 mega Newtons of thrust. This is a number that's still unmatched as of the making of this video, because once SpaceX is SuperHeavy fires and flies, it become the new record holder at around 75 mega Newtons. And that's just for now because it's likely to increase the N1's engines would steer the rocket via thrust differential and not through engine gimbling.
This is where the engines can provide more or less thrust on one side of the rocket to steer where it's going. It's actually a pretty complicated control scheme and relies on advanced computers to make it work reliably and advanced computers is exactly what the Soviet Union didn't have in the late 1960s. Their primitive KORD computer was pretty limited and alongside the rest of the avionics package, they just really weren't up to the task of managing 30 engines. Then those engines had very little testing and not to mention the rocket had to actually be flown in order to even test the engines in the first place. It was the ultimate in all up testing. One big flaw with the NK 15 is it had many pyrotechnic valves in order to save weight and complexity. So in other words, once they fired the engine,
they couldn't be refired. This led to only about one in every six engines being tested before flights with none of the engines that were tested being put on the rocket. Of course, they were basically just testing in order to validate manufacturing and ensure that there weren't big flaws with batches of engines. The second stage or Blok B would utilize eight vacuum optimized versions of the NK 15 called the NK 15 V which had an extended nozzle and air start capabilities and was more efficient at 325 seconds of specific impulse.
The third stage known as Blok V would four NK 15s each with about 450 kilonewtons of thrust and 346 seconds of specific impulse. These were direct descendants of the NK nine, that Korolev and Kutnezov initially developed. They of course, ran on Kerolox as well. Then there was the fourth stage called the Blok G, which was the stage that was to perform the trans lunar injection. It had a single NK 21, which again was a direct descendant of the NK 9 ran on Kerolox and had about 392 kilonewtons of thrust and 346 seconds of specific impulse. And lastly there was that RD 58 on the Blok D stage that we mentioned earlier with the Proton.
Now it was the final stage on N1 and it was intended to be a lunar breaking engine, kind of similar to how the US's Apollo service module would slow the vehicle down to put it into lunar orbit. And trust me on these numbering schemes Wikipedia, and a lot of other sources are simply wrong about which engines were on which stage. I had to go to my N1 expert, someone who has been studying the N1 for years and years, French space guy on YouTube and Twitter for the actual facts. Unfortunately, we don't have time to really dive into all the wild things that came from the N1, The problems, some of the largest rocket explosions ever, or the unfortunate and untimely death of Korolev before it would ever get a chance to fly. But long story short, there were four failed launch attempts, none of which made it through the first stage burn. Meaning out of all the engines we just talked about only the NK 15s would get their chance to run in flight on the N1.
But by this time there were already tons of upgrades in the works for different future N1 varients like the N1F and the N1M but their plans were never really solidified fully. Despite that many engines were fully developed, such as big upgrades to the NK 15 for an engine called the NK 33, which had some important new features like being able to be tested and refired thanks to simplified pneumatic and hydraulic systems. It also had more advanced controls upgrades to the turbo pumps, as well as the combustion chamber.
Come to find out this engine would be regarded as one of the most advanced engines ever made kind of still today. And for that reason, because it's so good. It actually still flies today in Russia on the R-7 family. Remember when we said there was a weird booster list version of the Soyuz? Well, this is the Soyuz 2.1 V and it started flying in 2013. The first stage is powered by the NK 33, but since it's a fixed nozzle engine, it has a 4 chambered steering engine called the RD 0110R to provide control authority. The second stage is the RD 0124.
It's actually a pretty cool little rocket, but now back to the N1, there was also work being done on a vacuum optimized version of the NK 33. This engine was called the NK 43. It was a nice upgrade to the NK 15 hitting an impressive 346 seconds of specific impulse. They had also already developed high-performance hydrolox, upper stage engines called the RD 56 and the RD 57. That would be the first hydrolox engines to be built in the Soviet Union.
They were impressive engines with extremely high specific impulse. The RD 57, I think was the first closed cycle hydrolox engine ever made, hitting an impressive 457 seconds of specific impulse and 392 kilonewtons of thrust and developed around that same time, the RD 56 would hit 462 seconds of specific impulse and 70 kilonewtons of thrust. But unfortunately after the N1s, four failed flights, Glushko, who is now the head of the Soviet space industry after Korolev's death canceled the program completely and ordered all the engines and the two unflown, but fully assembled N1's, to be scrapped. But since the NK-33s were developed by Kutnezov, who was in the aviation industry, Glushko wasn't his direct boss. So he just chose to kind of ignore his orders more or less.
So about 80 completed NK 33's were secretly taken to a warehouse in a single night in order to avoid becoming scrap. Now, we'll talk more about what happened to these secret hidden engines in a minute, but Glushko was moving on. He had his own plans for a super heavy lift rocket, and now that he was in charge, he got to do things his own way. A lot of stuff done in the Soviet Union was done in complete secrecy and things would come out of nowhere that would shock the world, insert the Energia rocket, the world's second most capable rockets only after the Saturn V.
And it was even more capable than the N1. Desiring super heavy lift launch capabilities, and also wanting to match the capabilities of the United States's Space Shuttle, the Soviet Union began work on the Energia rocket and the Buran orbiter in 1976, but it would be over 10 years before the system would fly. Powering this monster rocket was also the most powerful liquid rocket engine ever made. No, not the Saturn Vs F1 engine,
which was the most powerful single combustion chamber rocket engine. The Soviets developed a beast known as the RD 170. So now we get to see Glushko taking on his ultimate challenge. This engine would prove to be quite problematic, even for perhaps the best rocket engineer in the world. Glushko had already developed an engine called the RD-150, which was a cluster of six RD 151's for a project in 1974 and would never fly. But he'd use this design as the blueprints for this new engine.
He would also take a lot of experience and knowledge from the RD 270 and the RD 268 to solve a lot of problems despite all of his expertise and prior experiences Glushko met his match, trying to increase the thrust while attempting to make it capable of 7,250 kilonewtons of thrust. In fact, one time an engine blew up so energetically that it apparently sent parts of its turbo pump flying several kilometers away. Taming the beast was so troublesome that there would be proposals to replace it with the NK 33's. But luckily for us rocket nerds that didn't end up happening and in the end, Glushko was successful in hitting the target performance, reaching 7,257 kilonewtons of thrust and 309 seconds of specific impulse at sea level.
The RD 170 had a twin called the RD 171. Now the biggest difference between the RD 170 and the RD 171 is that the RD 170 could only swivel it's four chambers on one axis. While the RD 171 can swivel on two.
Which then would provide it with an extra axis of control, making it a better option for a single core rocket. They RD 171 would be the first of the two variants to actually fly on a rocket called Zenit in 1985. There was another version of the RD 171 called the RD 171M which had lower mass and increased reliability. It would go on to power the Zenit 3SL rocket 30 times. The second stage of the Zenit would utilize a fresh closed cycle Kerolox engine known as the RD 120, which could hit 350 seconds of specific impulse.
It was a fixed engine paired with an RD 8, which is a quad chambered vernier engine that provided control authority. The third stage of the Zenit rocket would have two different engine options that we've already discussed. Finally, some commonality, the Blok DMSL version utilized the RD 58 that as we mentioned, was the direct descendant of the original S1.5400 closed cycle Kerolox engine. The other choice of third stages was the Fregat SB,
the Fregat upper stage we already mentioned as the hypergolic stage on the Soyuz U, the Soyuz FG and Soyuz 2 and it utilized the S5.92 hypergolic gas generator engine. Here's a fun little fact about the Zenit is it also used to launch from a repurposed oil rig sea launch platform, much like SpaceX wants to do with their Starship. From 1999 through 2014, it launched 36 times from that sea launch platform.
So almost half of its 84 launches in total. The Zenit is still an active rocket, but hasn't flown since 2017. Now I wish I could report that the main use of those incredible RD 170 engines was lifting a super heavy lift rocket, but unfortunately it's life on the flamey end of a formidable super heavy lift launcher was short-lived. It would only see two flights on the Energia rocket once with the classified Polyus space station. And once with the Buran Space Shuttle. The Energia rocket consisted of four boosters each with a single RD 170. So there are basically four Zenit boosters strapped onto a massive hydrogen and oxygen tank, much like how the space shuttle solid rocket boosters were strapped onto the external fuel tank.
But here's where there's a big difference between the US's Space Shuttle and the Energia/Buran. On the Energia's center large tank had four engines, whereas the Space Shuttle had its main engines attached to the orbiter, so they could be recovered and reused, and it actually had no engines on that orange, external fuel tank. The Energia center tank was the biggest single tank. The Soviet Union would build offsite of the lau