Hi, it's me, Tim Dodd,
the Everyday Astronaut. I recently spent some time with Elon
Musk and SpaceX's Raptor engines and I spotted one of their previous Raptors
in a proverbial forest of Raptor 2 engines. So I figured now would be a good time to
go over some of the tweaks that SpaceX has made to the most advanced
rocket engine ever built. So today we're gonna do a quick rundown
on all the known changes we've seen with Raptor to date. We'll go over
their thrust and performance, how to spot the changes with
their external designs and
talk about how we expect to see this engine continue to evolve
in the future. Let's get started! First things first let's address the
elephant in the room. You're right. I'm not wearing a t-shirt. I'm actually wearing a dress shirt with
little tiny Raptor engines all over it. That's right. This is one of our long
awaited brand new dress wear shirts. If you love aerospace and also
love, or maybe need to dress up, these are definitely the shirts for you. Check these out and lots
of other brand new stuff, like our incredible 1:100 scale
model rockets and lots of other really cool new stuff at
everydayastronaut.com/shop. Okay, but for this video, I need to mention that we're going to be
talking a lot about the full flow stage combustion cycle engine pressure
and engine cooling techniques. If any of this stuff is
confusing to you, be sure. And watch my "Why don't rocket engines
melt" video and my "Engine power cycles" video. I promise those will help set the stage
and arm you with all of the knowledge to make this video more digestible. And this video is obviously meant to
help make the interview more digestible too. So watch 'em all and hopefully
you'll know everything you need to know. Let's start off with
an overview of Raptor. Raptor will be powering SpaceX's upcoming
Starship and Super Heavy booster. Currently the Starship upper stage will
have three sea level Raptors and three vacuum optimized Raptors, but it'll
likely go to six vacuum engines soon. The Super Heavy booster on the other hand
will be jam packed with 33ish Raptors, give or take a few, 'cause you just never know what
they're gonna do with the next ones, which will make it the most powerful
rocket ever with over twice as much thrust as the Saturn V rocket that
took humans to the Moon. Raptor is a liquid fueled rocket
engine running on methylox. So, liquid methane and liquid oxygen. The boiling point of each of these
propellants is very low -183 degrees Celsius for oxygen and -161
degrees Celsius for methane, which means they're cryogenic propellant. The engine utilizes the full
flow stage combustion cycle, which means both propellants
flow through a preburner, which then powers turbines,
which then spin the pumps. This has the potential to unleash the
absolute maximum amount of power possible from the propellant, or it could be tuned to actually
operate at lower temperatures inside the preburners or some happy
compromise of both. SpaceX is only the third entity to attempt
to build and manufacture this type of engine proceeded by the Soviets who built
the RD-270 in the sixties and Aerojet and Rocketdyne who developed just the
power pack of a full flow engine called the integrated power head
demonstrator in the nineties. Raptor is made out of many different
metals from inconel alloys to SpaceX's own SX500 alloy that we don't know a ton about
two copper aluminum and steel alloys. Just kind of lots of different stuff. As far as we know the materials haven't
changed all that much between Raptor 1 and 2, although they're constantly tweaking the
exact formulas for high performance and durability, some parts of
the engine are 3D printed, which is great for prototyping and
likely some parts will continue to be 3D printed, always. Although as
production continues to ramp up, they're starting to get rid of some of
those 3D printed parts for quicker and potentially cheaper manufacturing.
Raptor has an incredible gimbling range. Most rockets steer by swiveling the
engines on two axis' in order to point and guide the rocket, which
is known as gimbling. Raptor has the ability to swing 15
degrees on the Z and the Y axis. This is a pretty extreme
amount of gimbaling. I think it's actually the most of any
main propulsive engine. For example, SpaceX's Merlin engine could swivel
up to five degrees on the center, Merlin engine of the first stage of
their Falcon 9 and Falcon Heavies. The Space Shuttle and SLS' RS-25
can gimble up to 12.5 degrees and they had to do so to continually
send the power through the constantly changing center of mass as
the side mounted external
fuel tank and solid rocket boosters drain propellant and
when they were jettisoned. So 15 degrees is a lot and
not only can it move far, it can do so very quickly in order
to handle engine out capabilities. SpaceX practiced this intentionally
and not on their Starship high altitude test flights as a way to continually keep
acceleration as low as possible on the climb to 10 kilometers, they would shut down engines once the
engines reached their lowest throttle point. When an engine shut down, it quickly moved out of the way and the
other engines needed to gimbal quickly to catch the rocket and maintain control. These extreme cases are what drive
the gimbal limits and overall torque requirements of the actuators
that steer the engines. Raptor has been continually evolving
since the very first one off the line, but even before the major
redesign of Raptor 2, we saw some simplified Raptor 1 versions
sometimes called Raptor version 1.5. That first flew on SN15 and it was also
the kind of engines that they installed on Super Heavy Booster 4 and Ship 20. These engines stood out with
their green engine bells, which we've now grown accustomed
to as it's become the norm. This is caused by new materials
and a new manufacturing process. At the beginning of 2022, we
saw the first Raptor 2 publicly, which marked the end of Raptor 1. Raptor 2 is utilized on any new vehicle,
but as of the making of this video, Raptor 2 hasn't flown yet, but it will debut flying on the
first orbital test of Starship. So let's go over how to spot the
differences between Raptor 1 and Raptor 2. And talk about some of the
specifics between each one. Spotting the differences between Raptor
1 and Raptor 2 is actually really easy. First off, in comparison to Raptor 1, Raptor 2 looks like it's
basically not finished. It's missing that rat's nest of wires, adoring all sides of the engine
that was very obvious on Raptor 1. All of these additional wires were
necessary during the development of the engine. Each wire or tube was hooked up to
some kind of sensor like a pressure or temperature sensor, which helped the teams tune and tame
this extremely complicated engine. So in general, Raptor 2
looks much, much cleaner. Some of the valve work has actually
been unified into a few small boxes too. You can tell Elon's mantra of "the best
part is no part" is being played out heavily by stripping down
wires and sensitive components. It also makes the engines
more flame and heatproof. SpaceX is attempting to
remove heat shielding shrouds
entirely to lighten up the engine and to simplify them. SpaceX has also gone about removing
engine igniters where possible. Usually when your fuel and oxidizer
come in contact with each other, they still need a source of ignition
to ensure stable and smooth initial combustion. SpaceX used what are known as torch
igniters inside the preburners and inside the main combustion chamber. SpaceX was able to simplify and
presumably make the torch igniters in the preburners more reliable,
but Elon mentioned, they were able to remove torch igniters
from the main combustion chamber. This would be possible since the fuel and
oxidizer come into the main combustion chamber as extremely hot gases. Having a gas:gas interaction allows
for a clean and well mixed interactions of propellant that will happily
combust under the right conditions. It does however require extremely
precise and accurate timing. So the start sequence for Raptor is
insanely complicated compared to the start sequence for Merlin. It has to be perfectly precise
'cause each one realies-. Basically you're doing this, this delicate dance between the
fuel power head and the oxygen power head and if they get
outta sync then you can go stoiciometric in the preburners
and melt or explode the preburners. But wires, igniters and shrouds aren't
the only things being taken off. Some of the engines are missing some
vital parts entirely such as the gimbles. Raptor 2 will come in a few variants
at first and perhaps more later on. There will be engines that lack steering
gimbles such as the engines fitted to the outer ring of the booster. There's going to be 20 engines on the
outer perimeter and they actually don't require gimbles. Steering authority can be accomplished
by these center engines or perhaps with some thrust differential, or throttling the engines on one
side of the rocket or the other. There's also going to be the
vacuum Raptor engines on Starship, which are fixed as well. Removing the ability to gimble also
means they can remove the heavy actuators along with the actual gimble mount itself. Next you'll notice some flames have
been removed as SpaceX works on either welding as many connections as they
can, or just deleting them if possible. But as the design gets more and more
mature serviceability and access to everything isn't nearly as
necessary and by removing flanges, it can actually make the whole engine
more reliable and lighter weight as well. Lastly, perhaps one of the biggest fundamental
changes to Raptor 2 was the decision to open up the throat a little
bit. The wider the throat, the more potential there is to flow
more propellant through the system. But it actually reduces the efficiency
by reducing the expansion ratio, or the ratio between the area of the
nozzle exit and the area of the throat. The higher the expansion ratio, the more work the nozzle does to convert
high pressure into high velocity. Generally, engineers want as high
of an expansion ratio as possible, especially when operating
in the vacuum of space, but they're often limited to ambient air
pressure considerations for sea level engines. If all of what I just
said is kind of confusing, maybe watch my video on Aerospike engines.
We talk a lot about expansion ratios, flow, separation, and efficiency
in that video. In the future, I'll definitely do an updated video
all about this topic in general. But this opening of the throat has the
potential to increase the thrust of the engine despite its slight
decrease in efficiency. So I think it's time we actually compare
the specs of Raptor 2 versus Raptor 2, to see what effect all these
little changes have made. Seeing Raptor 1 and Raptor 2 side by side, we can see they're basically the same
dimensions and although they're the same dimensions, they are not compatible, you would not be able to use a Raptor 1
engine on a vehicle that uses Raptor 2 and vice versa, although
that would never happen. Each engine stands about three meters
tall and is about 1.3 meters wide at the nozzle exit. And they're actually pretty small engines
in the grand scheme of things compared to the RS-25 that powered
the space shuttle and is
what powers the core stage of the SLS rocket, Raptor is much
smaller and more powerful. And Raptor is extremely light. Now we don't know the exact
mass for either engine, but we do know Raptor 1 was right
around 2000 kilograms and Elon said, Raptor 2 is about 20% lighter.
So around 1600 kilograms. Next, their thrust. Raptor 1 was operating
at about 185 tons of thrust, which just so happens to be almost the
exact same amount of thrust as the RS-25 and Raptor 2 is already operating at 230 tons of thrust. This increase in thrust comes mostly
from the increased chamber pressure of Raptor 2. Raptor 1 was
operating at about 250 bar, which to be clear was already about the
highest operating pressure of almost any engine, but that's still
just the beginning. Raptor 2 is currently operating at 300
bar and they think they can get quite a bit higher yet. That is
absolutely an astonishing number. The Russian RD-180 was the
previous record holder at 267 bar, so Raptor is really
breaking some records here. This increase in chamber pressure, along with Raptor 2 having a
slightly wider throat area, has led to that increase
in thrust that we see. But changes to the throat and an increase
in film cooling has slightly decreased the overall efficiency of Raptor 2. Raptor 1 hit about 330 seconds
of specific impulse at sea level, while Raptor 2 is just a few seconds less, likely around 327 seconds
of specific impulse. Now that might seem like a step
backwards, and on paper, it is. But believe it or not, if we run the numbers on how
this affects the first stage, we'll see that having a
higher thrust-to-weight
ratio of the overall stage actually gets more work done than
having a higher specific impulse. This is due to something called
gravity loss or gravity drag. Since gravity pulls at everything
here on earth with one G of force, gravity is going to be eating up that
first 9.8 meters per second squared of acceleration. So until you produce
more than a 1:1 thrust-to-weight ratio, or until your rocket is making
more thrust than it weighs, it will literally go nowhere. And then there are massive increases in
the amount of work done when your thrust weight ratio gets above 1:1. If
our thrust weight ratio is 1:1, 100% of our thrust is spent fighting
gravity and 0% of our thrust can get us somewhere. And as you know, that means our net acceleration is zero. If our thrust-to-weight
ratio is 1.25:1, 80% of our thrust is still spent
fighting gravity and only 20% is used getting us somewhere with a
net acceleration of 0.25 Gs. But this produces infinitely more work
than a thrust-to-weight ratio of 1:1 since that wasn't producing any. So let's jump up to a
thrust-to-weight ratio of 1.5:1. Now 67% of our thrust
is wasted to gravity and 33% goes into accelerating the vehicle. So although we only increased our
thrust 20% over a thrust-to-weight ratio of 1.25:1, we actually produced twice as much
work giving us a net acceleration of 0.5 Gs. And that's approximately the thrust
increase from Raptor 1 to Raptor 2. Actually, Raptor 2 has about
a 24% increase in thrust. So they can actually get over double the
amount of work done at the beginning of the first stage burn
when it's full of fuel. Obviously getting twice as much work
done is much better than a percent or two more efficient. Okay, that's the direct comparison
of Raptor 1 versus Raptor 2, but this is SpaceX. We know they aren't done pushing this
thing and Elon already has mentioned many improvements they're currently working on, so let's wrap this up with what changes
we can expect to see in the future. First off, I think the number one thing we're going
to see is SpaceX continue to try to make Raptor more and more
production friendly and cheaper. Elon is obsessed with
reducing the cost per unit, but I know price doesn't really seem all
that important when the rocket is fully reusable because they can
just reuse it over and over. But SpaceX is dreaming big and pictures
these vehicles being about as common in the future as airliners are today.
In an attempt to simplify the engine, SpaceX is also attempting to remove
throat film cooling as those of you who watched my "Why don't rocket
engines melt" video might know, it's common to inject extra fuel directly
into the throat of the engine to help cool it. Removing throat film cooling can be
accomplished by being more conservative in other areas, such as increasing
the head in film cooling, otherwise known as injector film cooling, or even just going further fuel rich in
your overall main combustion chamber. SpaceX is currently studying and
evaluating whether or not it's worth it to simplify the engine.
Despite the performance hit, it will take from additional
head in film cooling, but with the obsession
to simplify the engine, perhaps this will be something we see in
the future. Another thing to look for, we definitely expect to see Raptor
increase chamber pressure and thrust. We know they're aiming to
reach about 250 tons of thrust, which would likely be closer
to 330 bar in the main chamber. SpaceX has hit 330 bar in a test before, but sustaining that will
take additional improvements. One of the biggest things to remember
is overall Raptor is still very much in its infancy. Elon has mentioned how the Merlin engine
has been evolved to be over twice as powerful as when it first came out, but that engine has pretty much reached
its full potential. So in this case, Raptor is still just
at the very beginning. I expect it to continue to become
more powerful, lighter, more reliable, and cheaper, and I expect it to
do all of these things in a hurry, now that SpaceX has the means
to do so. So what do you think? Do you think Raptor 2 is a nice
big improvement over Raptor 1? Or do you kind of think
this is just the beginning? Or maybe you think Raptor is a dead end
and we'll actually see SpaceX go back to a simpler engine, more like
Merlin or something someday. Let me know your thoughts
and the comments below. I'm sure you noticed the incredible
Raptor 1 and Raptor 2 renderings in this video, those were thanks to Izan Ramos and
Casper Stanley who are just some of the most incredibly talented
3D artists out there. And I also owe a huge thank you to my
Patreon supporters for helping make videos like this and everything else we do
here at Everyday Astronaut possible. If you wanna show your support and gain
access to our discord channel or early access to videos, head it over
to patreon.com/everydayastronaut. And while you're online, be sure and check out all the incredible
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we've got other cool patterns too, including grid fins, dragon
capsules, and lunar landers. But also lots of other really cool stuff
like some new merch for tiny humans under our "Space Cadet"
section, some nominal socks, or our 1:100 scale Falcon 9 model rockets, well at least when they get back in stock. Find it all at everydayastronaut.com
slash shop. Thanks everybody. That's gonna do it for me. I'm Tim DOD, the everyday astronaut bringing space
down to earth for everyday people.
