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
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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.