Hi, it's me, Tim Dodd,
the Everyday Astronaut. I try really hard on this channel
to not, you know, be too hyperbolic. I don't want to overuse words like
groundbreaking or game changing or even novel because frankly there's very few
things in the aerospace industry that are truly any of those things. So, when
a small company based out of Kent, Washington reached out to me
claiming to have a fully reusable, groundbreaking novel rocket, I
was obviously quite skeptical. So what if I told you there is a small
little rocket company that you likely haven't heard of that is not only
claiming all of these crazy things, they're already building it and
testing it at frankly a ridiculous pace. And best of all, at least to me, they're utilizing the Aerospike
effect in a genius way to help make a fully reusable upper stage. So today I'm gonna show you around Stoke
Space's headquarters and their test facility to help reveal
their super unique rocket. I'll explain in great detail how it works
from their actively regenerated cooled heat shield to its unique offset
geometry for precision re-entry landing, but also how its awesome engine is
integrated into that heat shield. And best of all, we're actually going to see them
fire up this incredible engine. And that's not all stick around to the
end because their CEO Andy Lapsa dropped a bit of a one more thing on me with a
little detail that I couldn't believe. There's a ton to talk about and see. So let's get started. Hey Tim, come on in! How's it going? Good. Nice to meet you. I'm Tim, nice to meet you! Let me show you what we're working on. Sweet. So I feel like I gotta kinda learn about
how you guys are gonna doing this cause I don't have even the slightest clue
on what you guys are working on. Well, let's do it.
Let's get into it. Yeah. So this is what we're building in some
sense it's a traditional two stage to orbit, vertical takeoff, vertical landing, first stage looks all very familiar to
what the industry has shown already. Yep. Second stage goes on orbit, deploys base craft can do a number of
things on orbit, can move around orbit, can acquire assets on
orbit and then can bring them home. The re-entry is more or
less a capsule style, ballistic re-entry, although we do have cross range built
in and then we can do precision landing. The engine has to do a lot of things
now that are not typical for upper stage engines. Right. It's gotta
obviously do the deployment mission, but it's also gotta do the reentry
burn and then terminal descent in atmosphere. So it's gotta throttle deeply. It's gotta work inside the atmosphere,
it's gotta work outside the atmosphere. The engine's gotta do a lot of
things, so that's why it looks weird. Yeah. Yeah. And I'm self spoiling here, but based on that, based on being an
in space engine and a sea level engine, I know there's only one
engine that can kinda do that. Why don't we go take a
look at all the stuff, because I think there's probably a lot
of things we'll probably learn seeing it up close. Awesome. There's some hardware here! Oh
man. Okay. You weren't kidding. There is, there is hardware here already. Yeah. So I mean that's, that's the name
of the game is design, build, test, iterate as fast as you can possibly
do it. And to do that quickly, you've gotta be vertically integrated. You gotta own your dependencies and
be able to move as fast as possible. So we tried to build that
capability up as fast as we could. Everything you see we've built
in about the last 18 months. We're definitely already out of space and
using other space to play frogger with different parts and stuff. But this is our serial
number two engine build. We'll see, I guess, the business
end of it in a little bit. It's pretty cool. So if you don't mind me asking, as we're kind of looking at
the actual hardware here, like what are those are
struts to hold... what? These are the thrust takeout. Oh, okay. One of the cool things about
this design is you think about you think about thrust being
generated and then how it works. Its way up the vehicle, all of that thrust load has to make it
to the outer skin of the vehicle and goes up basically through the
tank structure, right? So one of the cool things about this
architecture is the thrust is already distributed around the perimeter. And since we don't have to gimble the
engine, like if you gimbled the engine, you'd have to bring all that thrust
load into a center point and then redistribute it all out. Structurally
is very inefficient. Yep. So here we got the thrust all the way
on the perimeter and we keep it there. So our thrust takeout is little
tie rods.That's all it takes. Huh. And curious why they are
not rigid. Why do they move? Well, they become rigid, right? Just for installation that
they're on bearing and stuff. Yeah, yeah. It gives you, you know, the small little micro adjustments that
you need in order to just precisely true in. Yep. Got it. Got it. Yep. And then, you know,
it's on bearings. Okay. It's on bearings because this is
designed to take a linear load. It is not designed to
take a moment or a torque. Right. So you put it on bearings to eliminate
any torque. Otherwise you damage the-. Gotcha. Yep, yep. Yeah. Even
a degree or two of torque. Gotcha. Exactly. Okay. So 30 thrust chambers, right? 30 Thrust chambers. Wild, wild, honestly. So where's, which side of it will the the
turbo pump hang off of here? I believe the, at least the way
it was clocked on the last build, it's over there. Yeah, you can kind of see,
well maybe a little bit more. I don't know if you'd have anything
to be able to see it at this phase. It looks like you got kind of a QD
[quick disconnect] connection over there. So this is the one you're
building to hop, right? Yep. So you're already getting to the point
of having to have disconnects and, or no, you'll probably keep it tethered, right? Nope. You're going for it already. No tethers. No. Holy cow. So you're already looking on
your second one to, to have, you have to develop
your QD and everything. Yeah, I mean, the nice thing, it's such a modular design that it
will be our second formal build, but parts can go in and out
of it all the time, you know, so we've been doing that on the
engine, on the stand. We've got, I don't know how many pumps we've been
on and off of that stand as we, you know, continue to dial things
in, but it's very modular. Wow. It's, it's big. And that tank,
could we go, can we check out the tank? That's, that's big. Oh,
and so it does taper. It does taper. This is the real deal, man. It tapers. And so, so your heat load is- you shouldn't
really be experiencing too much heat. It's kind of like a, a
capsule, like a traditional, your second stage is is almost
like a traditional capsule. Yeah, that's the idea. Crazy. Make it a traditional capsule base first. That's where you take all
the heat load of reentry. And that minimizes the amount of surface
area that you need for, you know, whatever your thermal protection
system is. So we do that. It has some other nice byproducts of this. One of them is all of the inertial
loading is in the axial direction, both on the way up and on the way down. Yep. You don't have to have it. It's not going horizontal or
anything and having to do-. Yeah. So that's nice if you're,
if you're a payload, it's nice. You don't have to deal with the
change in acceleration vector. It's also nice from a structural
efficiency standpoint on the vehicle. You don't have to design for
those transverse accelerations. That's actually something that's being
talked a lot about topically right now with, on Twitter is SLS out on the, on the launchpad with the hurricane
coming in, people are going, "why can it only, you know,
it's going supersonic, why can it only handle 85 mile
an hour winds?" It's like, that's in one direction. It can go, it
can handle a lot of dynamic pressure. It's not meant to have high wind shear
forces coming in from the side of the vehicle, you know? So that's, so
this is the same thing almost. It's not meant to ever fly horizontally.
It's always gonna remain vertical. Yep. So that's some of the
structural efficiencies that
we gain not having gimbals is another element of structural
efficiency that we gain. And so kind of as you
go through the system, there's these little pieces
that allow the system level solution to be pretty highly efficient. Even though you've built in what's
traditionally thought of as pretty heavy architecture for the engine
we're able to do it in a mess that makes sense for an upper
stage. It's pretty cool. So how does the... So during reentry, are you actually going to be flowing
cryogenic fuel through the walls of the heat shield and everything?
Or how does that? That's what, that's what it
is. It's pretty cool right? Right. And how does it, what pressurizes
that, like how do you keep it flowing? The same circuitry that runs the engine. So do you actually have to spool
up the turbo pump a little bit to, to keep it moving and really? But I mean, it's an
expander cycle. So you get, instead of taking the energy
out from the chambers, you take the energy out
from the heat of re-entry. The heat of re-entry!
And it spins itself, itself up. No. Okay. Okay. That's really cool. That's really,
really because people always ask, "why don't they capture that energy?"
And that's basically what you're doing. You're capturing energy to power
a regenerative cooling structure. Okay. I love that. Okay, let me take a
second here and explain why this is so, so cool. Stoke's upper stage
engine is using the expander cycle, which as those of you have watched my
"How to Power a Rocket Engine" video may know, it's where you take the heat
from the engine to heat up the fuel. So it changes from a cold and dense
fluid to a high temperature gas like fluid. And then that now hot high pressure
gassious fuel will flow through the turbine to power the pumps. It's a very cool system since it uses
what could be just wasted heat energy, it recaptures it and uses
that to power the pumps. But the same principle is being
used here for the heat shield. So basically after exiting the pumps, the fuel will flow through the heat
shield, into the combustion chambers, and then some of it goes
back to power the turbine, which powers the pumps before being
dumped overboard. So on reentry, as the vehicle comes
back into the atmosphere, it compresses the oncoming
airstream so much, it'll heat the air molecules up into a
plasma and you have to deal with that extremely hot re-entry heat somehow. So instead of a traditional heat shield
that might ablate or basically flake or intentionally burn to
take heat away with it, or a strong insulator like the
silicon tiles on the Space Shuttle, they're going to flow some cryogenic
fuel through the heat shield to cool the metal down, similar to the regenerative cooling
inside the combustion chambers of the engines. Now, the beauty of this system is that
because it's an expander cycle engine, this heat shield can more or less
self-regulate and power itself. As it heats up, it'll heat up the fuel inside it and then
that will flow towards the exit after flowing through the turbine,
the turbine will spin, which will spin the pumps and begin to
move more propellant through the heat shield faster.
The hotter it gets, the more fuel will flow through the
heat shield and through the turbine, which will then increase the speed of
the pumps and increase the flow rate of propellant into the heat shield
to cool it off more and more. It's truly a genius
double use of the system. The engines won't light up during this
because the fuel is being routed through the turbine and none of it is going
into the engine injectors and into the combustion chambers for this phase. So the fuel is only being used to cool
the heat shield and the combustion chambers and then used to power the
pumps. But then during the landing phase, obviously they'll go back to
the normal routing of fuel, which will have some of it go through
the turbine to power the pumps, but the majority is routed into the
combustion chambers along with the liquid oxygen through the injector to actually
power the engines to propulsively land. And we'll talk about
that more in a second. So, I mean, I think, I actually have
not seen that in the literature before. You have seen there are a couple
different ideas. Everybody, everybody tried everything in
the fifties and sixties. I, I think we're in like this renaissance
period where people are actually having ideas and then building
stuff. That died for a while, but in the sixties for a long time
I was like, "man, every good idea, not only somebody already had it,
they already tested it". Right. If you dig deep enough, there's
test data on everything. Everything I know.
Yeah, that was a hayday for sure. It had been proposed, you know, different active cooling solutions have
been proposed. Water is a, you know, attractive candidate for a
couple different reasons, but it requires in totally
separate circuitry, new tanks, new pumps, new pressurization systems and
it's all drag on mass for all of the rest of phases of flight. And what this does is gets rid of all
that drag on mass where you're actually using it for every phase of flight. Yes. You're yeah. You are the
same thing that makes it go up, allows it to come down. That's right. That's amazing. Yeah. And if we couldn't
find that solution, I'm pretty sure this wouldn't make sense. Yeah. Yeah. So, and the another
thing too, you're not actually, you're not doing like
transpirational cooling or anything. You're actually just
keeping it all, you know, in inside the the coolant lines. Right? That's right. Yeah, that's right. It, like you said, it could become transpirational
cooling if there is an issue with it. That's right. If you get like a little
micro crack or something. Then it, then it does and it over cools
and then it just keeps going. Yeah, just keeps going. You might
wanna fix it for the next flight, but it'll clearly survive re-entry. Yeah, yeah. Or I mean, honestly maybe, but you don't fix every little micro
crack on an airplane wing every flight. Right. You have scheduled
maintenance, you track those things and... You have acceptable, you have
acceptable bounds of what is- wow. That's all high quality
problem down the road, right? Where we start to deal
with those problems. Yep. Which is cool. Wow. So what's- Is this stainless steel? Stainless steel. And what drove you guys-
let's, can we get, let's, let's get a little different
shot on this here. Let's, let's walk around a little bit here. It might be cool on the forward
end also. I mean we can. What drove you guys to do stainless
steel instead of you know, carbon composites? By the way, us about the tie rods. So
these are the, the tie-ins for tie rods, right? It's upside down, isn't it? It's, yeah, it's gotta, yeah. Yeah, yeah. Turn 90 degrees. Okay. Got it. Got it. Yep. Okay. That makes a lot
more sense now. Okay. So what drove you guys to do
stay stainless steel instead
of instead of anything else? Aluminum or carbon or...? Well I would say that our single decisive
reason is manufacturability. Yeah. and availability of material, right? Yeah. So especially these days
where you do have supply crunches, you know, every day
stainless steel, we can source that, no problem. Sheet metal is
amazing. It comes to you, it's, first of all, it's commoditized from
a number of different suppliers. It comes with amazing material
properties out of the gate, thin walled pressure vessels, like
to have good material properties. and then from a workability and
manufacturability standpoint, almost nothing beats it. Right? Yep. So those are reasons the question
then, what is a mass impact, et cetera. and, you know, you can basically polish a
turd on that and analysis will produce, you know, garbage in, garbage
out or inputs determine the outputs, right? Yep. Yep. so there's a number of ways you can
look at it and our standpoint was like, okay, it's a close enough trade, we're
just gonna optimize for manufacturing. Yeah. And that's what we did. You can spend years and gobs of money
just even trying to figure out which metal two is like at the end of the day, you're chasing a couple
percentage points or whatever. Yeah. Yeah. Okay. Just
go build. Yeah. and, and the other thing I think that's worth
mentioning on the upper stage is it's coming in the skin will get
warm, stainless can, you know, holds its material properties at much
higher temperatures than like aluminum. Yeah. And one of the things that I think is
really cool about our architecture being actively cooled, it's gonna come in
and land it actually be cold, not hot, right? Yeah. But like if you look at
shuttle, shuttle came in those tiles, it's passively cooled. Yep. Yeah.
That protects it during re-entry, but it's also absorbing all the heat. It's absorbing all the heat. And that heat over time
is soaking in. Yes. And they actually had to plug in a water
cooling circuit in order to protect the aluminum structure Yep. From
losing material properties
as the heat soaks. Yep. So anything about how fast can I approach
the vehicle to service it or start getting ready for the next mission you
gotta deal like ceramic tile solution has to deal with all that.
Yeah. You know? Yep. Well, and like you said, you know, stainless steel can handle
pretty high heat loads, like Centaur upper stages have
survived intact, you know, and made it back through reentry
in one piece, which is crazy. That's really thin too. That's really thin with no additional
consideration for reentry, you know, and Right. Obviously you guys are
gonna be having pieces of it Yeah. Piece pieces. Of it. Yeah. Yeah. Pieces of it. Yeah. That's
true. Yeah. Not completely perfect. But so you guys are gonna be having still
another layer on top of this that is your active heat shield slash. Yeah. Yeah. This is
just tanked dome engine that assembly is installed,
you know, downstream of that. And then we'll go, I can, I can show
you these shield <laugh>, let's go. Look at it. Yeah. Sweet. Okay. So this is our heat shield. It you can see the, the shoulder of it is the ring that
you see in our hot fire videos, these holes are cutouts for the thrusters. and then the rest of this is
designed to enclose really all of the vehicle systems. So the turine
machinery on the engines, valves pressurant bottles avionics controls. All of the things it takes to run the
vehicle are all kind of housed in a volume between the heat shield and the tank dome. Right. So the bottom tank, is that your fuel tank or is
the bottom tank the oxygen tank? Yeah. And then similar to Starship, we
do have, they call 'em the header tanks. We call 'em the landing tanks,
but tanks, inside tanks Yep. To do different phases of flight.
Okay. We didn't talk about, okay, so we were talking about the kind of
the cool things about going up and back base. Well nose
first and base first. Yep. One of the things that's
nice that we avoid is the cryo fluid management of the
swan dive maneuver. Right. It's all flowing in the same
direction. Always in the tanks are. The same. It's always inertial loads
are always in the same direction. Pumps are being primed nicely. Right.
We kind of avoid that challenge, which you know, is solvable. Starship
is solving it. They did, right? Yep. But when we were architecting this
in the basement, we're like, oh, that seems like a hard problem. We
don't wanna do that <laugh>. Yeah. Exactly. Okay. So, so all your, all your loads are gonna be
the same fluid transfer loads, everything is flowing the same direction
throughout re-entry and lift, liftoff, which is, which is huge. So
the, obviously you must, okay, so I'm trying to figure
out, so the, the gaping, so there is that much space between the
bottom of the bulkhead at the bottom of the dome, and enough
room to put a turbo pump. And all your landing tanks and COPV's, avionics all fits underneath
this heat shield. Well, I guess above the heat shield
between the bottom dome. Yeah. Yep. Seems like a really tight package. It's a aerospace vehicle. <Laugh> <laugh>. Have you ever climbed in the
wheel well of a 737 or something? There's a lot jammed in there, right? Yeah. Yeah. Yeah. So, dang. So is this actually
actively cooled already? Is there the, so there's the channels through here? Yeah. You can kind of
see, you know, you can oh, see the channels in the shoulders
and you can see 'em, you know, different grind, grind levels. Right. So. So then at the top, what's happening at
the, at the very, the very middle there. What's. So it's an open expander, so you gotta
do something with the turbine drive gas. Yep. and so this is where, you know, some of the nuances of the
aerospike come into play, but one of them is if you
read the whether it's a J2-X or the X-33 engine performance is actually better when you have
some amount of base bleed. Yeah. Right? Yeah. So the aerospike architecture actually
lends itself quite well to an open cycle. Yep. Yes. Okay. So and you want to
fill that, that little wake? I believe. So that whole is turbine exhaust. Oh. This, it's almost getting
to this point of why, like, I'm starting to the point of going,
why hasn't this been done before. I don't know. Because it almost seems,
it almost seems all, so. Let's see if we can do it. Wow. Have you, have you ever
considered the option of, before you worry about
developing your own booster, just flying the upper stage
on somebody else? And. It would, so it would take some doing One
of the reasons that we are fully vertical is that interface
is non-trivial. Yeah. There's not a whole lot of companies
working with hydrogen, although we can do, we actually do have a fully
mobile hydrogen infrastructure. Cause we're gonna fly
hopper. Right, right. Right. It's already mobile. Yeah. It already
fills up the tank. Right. So we can do it, but the interface is pretty non-trivial. So we know we
want to go there anyway. It's the right move for
efficiency. So that we're, we're just focused on doing it that way. Wow. Okay. I'm, I can't wait to see this thing
fire. That is, that is amazing. And I'm a little bit
confused. How do you get from, sorry, I'm just trying to get this
all together in my head. What, at what point is this only
always your bleed line coming through here? Or. This? Okay, so bleed comes
out the hole, but this, the feed is all going from
Center Outward. Center outward. So this is all like
liquid or cold hydrogen. Okay. That. That eventually feeds the
nozzles and drives the pumps. The, the nozzles. Okay. And where. I'm trying to like those, the, the manifolds that we see
where the chambers are, is this replacing that or is
there another one behind it? Nope. So that was just a test
stand. Yeah. Okay. So the, and then the additional bit
of expansion that we get here. Yeah, you can think of
that thing as, I mean, the other sidehas a
higher side wall, right? Yup. But that thing is like a sliceof
three of these thrusters. Yep. And now it's just canted in
to make it to begin a radius. So, and then this is the little extra bit of
expansion that we gain is from here to here out of. The expansion that we gain is from here
to the other side to the other side. Side. To the other side. All of this gets it's not a high pressure,but it is a pressure, So all of this is providing thrust in space. There's pressure against this whole surface. That hurts my head. That's the aerospike! That's the aerospike! But in my, in my
mind, an aerospike always goes like, it's just the actual walls. The sidewall has this, you know, this very optimized contour.Blah, blah, blah, blah, blah, right and um, that doesn't make sense for the reentryphase, right? Right, right. So this whole thing is not "how do we design aerospike?" It's how do we bury a second stage engine into a heat shield. Into a heat shield? Yeah. Yeah.
Right. So what happens inside the, the thrust chambers during reentry are,
is there, does the wake kind of come? It's really cold too. It's actually cool too. So you're basically dead-head it. Yep. We've got stagnation gas in there. Yep. But the walls are actually cold. Walls are still flowing. So they're
basically a heat shield themselves. They can already handle the
internal temperatures of
combustion handling reentry temperatures. Is is a walk in the park? I hope! Holy cow. I, this is
getting more and more. Just the more I'm thinking about this, the more I'm Why has this been
done before? It's so cool. And I love the, the canted angle, or I
don't know how you'd describe it. The, the off the skew of it. So you can
have, it's like a very exaggerated, blunt body re-entry that you
would normally have on a capsule. So you actually can provide a
fairly healthy lifting vector from a, not a wing, from not a wing.
And it's still your heat shield, it's still your it's just like
everything is something else. Yeah. That should be the name of
it. That should be "Stoke. Everything is something else.". I like it. I, I like it. That is just so, so cool. All right. What else do you have
to show, show us here. Well, let's interrupt again here real quick
to explain how they can precisely steer this thing without using wings or fins. And instead they can just use the offset
and the mass and the offset and the heat shield to provide a lifting
vector. This concept isn't new. In fact, pretty much all capsules have their mass
offset from the center of the capsule. So they can do exactly that steer and
control their reentry to some degree. In fact, the Orion capsule on Artemis one did a
fair amount of trajectory correction in the atmosphere during its
ballistic skip reentry. If you have your center of mass offset
from the center of your heat shield, there will be a lifting vector that's
perpendicular to the direction of travel on one axis. Then by rolling the
capsule, you can actually steer it. This is especially useful for raising
or lowering your trajectory to extend or shorten where you'll land down range.
And by rolling it on its sides, you can even steer left or right too.
But stoke took this a different way. By having a pretty major
skew of their heat shield, they're able to get a similar
lifting vector like a capsule, but with a more cylindrical body. But they can still provide the steering
authority to be able to precisely target their landing site. This means they don't need any additional
mass for aerodynamic control features, just the offset and the
skew of that heat shield. Then they can just use the reaction
control thrusters to roll for steering. And it should be able to
precisely target its landing site. This is our little machine shop. we've
got the capabilitiesto do most things. Four axis, five axis, lathe, mill. There's a, I mean, that's a fresh
chamber coming out of there. You gotta fresh chamber. There is a brand new baby being
born into the world right there. Yeah. And that, so that's being,
was that being CNC'd? Yeah. At this point. Geez. Yeah. So it comes out of print. I
mean, you're familiar with the process. It comes out of print. Fact probably
have some raw prints back there. And then all of the sealing surfaces and
mating interfaces and things like that always need still final
machine. Right. That's, what we're doing! I love it. The machines in the back is where we
do EDM [Electrical Discharge Machining] you're familiar with EDM,
we've got EDM in house. So that gets machine down into
your final thrust chamber and, and you're using a similar, you're
using copper lined thrust chambers. what's the exterior? Is it like, what's
the exterior of the chamber made out of? It's just copper. It is copper too? Low pressure. So. Oh. You don't need a huge structural jacket. Right. Okay. And there's
another thing, it's like, dang, you don't have to do the fancy,
you know, meddling of bi-metallic. Yep. Bi-metallic stuff. Right. That's a tough, it's
still a tough nut to crack. Right? Yeah. Yeah. Wow. Low pressure. The low pressure thing
is coming around as a. Well that's everything. Right? It
helps the open cycle be more efficient, because you don't need as much
energy to drive the turbines. Yep. Again, as long as you can get
a giant expansion ratio. Right. Unbelievable. I mean, the
scale of this thing, it's, it, it's, it's not small. It's not Starship. But it's not small. No, it's not
Starship. But it's not small. It's not small at all.
That's, and how, I mean, how tall is your vehicle going to
be when it's all fully stacked? A hundred, hundred less. Yeah. Wow. That's a hundred
feet for those of you in, in America. Yeah. 30.
Yeah. 30, exactly. Yep. Yep. Wow. And, and 12 feet. So that's what like 3.7. Yeah.
A little more. And it tapers, so your booster's actually a little bit
skinnier than your upper stage until the. Booster's skinnier than it. Tapers out, flares out a little bit. Does, does that booster design help during
reentry? Does that booster actually help? Or is that. Yeah, so I mean, so you, you're familiar
with having the grid fins out there, moves center of pressure back and gives
you the control authority. But yeah, that taper, moves center of pressure back. At least at subsonic regimes, I'm sure. Probably not a lot during hyper
or supersonic. Yeah. So then, so that probably helps have
a slightly slower terminal, terminal velocity too terminal
velocity. Yeah. Cool. Do you, are you, do you have any aerodynamic
control surface for the booster? It will, yeah. I mean, you've got
to drive it to precision Landing. So Yeah. Yeah. Are are they
gonna be canards or grid fins? Not Canards. Not canards. Grid fins
though. Or some, some cool. Yeah. I, I still like, I still like
how, and maybe you don't like it, but I, I appreciate how Blue Origin had the,
the ring has the ring on New Shepherd. Yeah. I think that's a really cool
little design. Cause it acts as a, as a ring stabilizer and has the
room to pop out those extra fins and everything. It's a pretty, pretty slick
little thing. Yeah. Yeah. and I, I like. It's a cool vehicle. It really is. It's you know, from a
stability perspective, Jeff's
talked about it on record, but from a stability perspective,
it's short and stubby. So it's Right. A non-trivial problem to solve. Yeah. Getting that thing to
fly forward and backward. Yep, yep. It's pretty,
it's pretty cool. And yeah, this almost seems like the, that that
taper just sort of reminds me of that. And I really, I always thought that
designer was really cool. Yeah. You know? Yeah. Yeah. I mean, we were talking about, you were talking about it
for high altitude flight, like on paper Rocket equation. This
thing can go to 400,000 feet. Yeah. Well we were real excited about that. Yeah. And then once the game down to actually
designing that mission, we're like, oh, well we gotta add this, that,
the other thing, or, you know, change the OML (Outer Mold
Line), and then we're like, that's a whole new vehicle. That's a totally new. Yeah, we'll just fly it. Yeah. Yeah. Just do short hops and not worry about
actually getting it up to speed. Yep. That's amazing. Wow. Well, is there
anything else that you can think of that, that we can Well, I was gonna. Well I was gonna say if we go off camera. Yeah. We can walk through
turbo pumps and chambers. Yeah. And show you those things. Yeah. And we can talk
about off camera. Yeah. After a little tour of the secret sauce
stuff that unfortunately I legally can't show you. We packed up and
headed out to Moses Lake, which is about a three
hour drive from Kent. This is where they have their test stand
and where they're currently testing their first developmental
engine. And best of all, they were priming the engine
by the time we got there. They were getting it ready to do a test
fire for us while we're there. Well first off, where are we right now? We're in Moses Lake, Washington. This facility we've built up
really from scratch in the last 18 months or so. Moses Lake is a really cool small town
eastern or central Washington that has a surprising amount of aerospace
and kind of technical community around it because some old military work, Boeing and Air Force use it for
different trainings and test flights. And it's got a humongous airport,
which is right over there, or at least the runway is humongous. It was actually a backup
Shuttle landing site. Really? Yep. No way. So there's lot of, there's a lot
of infrastructure in the town, which is really cool, and talent and
it's a great place to build and test. That's awesome. How far is like, it's,
it was a three hour drive out here. About a three hour drive. Yeah. So. Are there any flights that popped
down into here from SeaTech? Not not commercial, but you know, when, when you start flying around on
a jet, you can land yourself. Hey, maybe someday. Maybe someday. Yeah. So we wanted, look, we wanted a test facility as close as
possible to engineering and manufacturing and you know, it's a three hours
drive, which takes some time, but it's not a plane ride,
it's not a time zone change. And we shuttle parts back and
forth every day just about. Yeah. Yeah. So. Helps our speed and iteration. So that's it. This is our second stage stand. Yeah. So it's designed to do engine
testing like we're doing. We can also install the
vehicle itself and do hold down tests up there
Yeah. Wanna I go up and. Yeah, I do. Check out the goods? I was already itching. I'm like, I gotta see this
thing up close. Now one of the, I think one of the crazy things for me,
oh, this is, this is a cool shot shot. Just looking up underneath
here. Look at that. Oh man, this what's crazy is from here,
you can't even see the, oh, there's the turbo pumps. Yeah. Pumps are kind so
cute. Yeah. Aren't they cute? They actually really are. I mean,
honestly, like they're, they're just, wow, that's amazing that those,
those guys can power the whole thing. Yeah. The fuel pumps about
a thousand horsepower. And fuel pump or ox palm
doesn't need as much power, but
Turbo Pumps are amazing. There's just tons of power packed
into a small little volume. Right? Yeah, and what, what's amazing to me
is that you guys are brave enough to, to use hydrogen, which frankly is kind of
rare these days, you know? Yeah. It's it's not in
vogue at the moment, but look, I think for
what we're trying to do, it's absolutely the right propellant. It has amazing efficiency
specific impulse gives us the elbow room and performance
that we need in order to perform these reuse functions with the
upper stage, right? You think about, think about earth and how kind
of lucky we are to be able to escape earth's gravity well, with
chemical propulsion We can do it. But it's like right on the edge. Right? I know. We're
lucky. It's like 5% more, even a little bit thicker atmosphere.
Just get that much nastier. Yeah. We're just at the cusp
of like, it's, it's, it's doable and then it makes it a
lot harder when you're trying to reuse everything, you know, that's. Yeah. So that's the thing, right? Like every pound that you put on the
vehicle that has to be dedicated for reuse is a pound that you can't use for payload. So there's kind of two things you can do. The first thing that you
can do to build in the, the I guess the margin
that you need to reuse is use like massive economies of scale,
which is what Starship is doing. Or you have to find elbow
room somewhere else. And we find that with hydrogen gives
us enough you know, extra performance. But you don't, you don't find it to be
too cantankerous to, to handle. And. No, it's definitely a specialty
skillset, but I think as with anything, with practice, you can get good at it. So we we have a team that's operated
hydrogen before and, you know, the new people we bring in
now have that expertise also. And we've run, I mean, on month of October we ran 70
engine tests with hydrogen. So. In the month of October
you've run 70 engine tests? Yeah. Now we're. So over twice a day? There's a short duration and we're
Oh, yeah. And that's average too. So test days will run more
and then we have you know, build in some down days for, look, we're also in an active
construction zone as you've seen, so we've got other activities
we've gotta do too. So, there's a lot going on that's. Geez, that's just, I find it's just
hard to f I feel like, you know, I don't know, maybe this is the old
school aerospace thinking in me, but like, I feel like hydrogen is just so nasty
that people are lucky to fire up for engines a couple, you know, it just seems like it's just so finicky
and people are so afraid of it now. And you know, of course right
now topically like SLS and, and the Artemis program
has, you know, had their, the woes with hydrogen
already. But I mean, I also don't think they're firing the
RS-25 off on average twice a day. No, I don't think, I know they're not firing
the RS-25 off on average twice a day. I mean that's. Yeah, I think it it also depends a little bit
on where you're at in the development schedule, but I think
practice is A number 1, practice and design to be able to do
this is the most important ingredient and then you have to be able to
accept of risk posture that allows it, right? Yeah. But yeah, I mean, need to design your systems and your
safeties in place then that works. Yeah. That's amazing. You're gonna try and see if we can light
this engine engine here today for us. Yeah. Here we go. There ya go! Yes! That was awesome. Yes! I mean, that looked great. That was, like
seeing all the little thrust chambers. Isn't that wild? That's so cool. Wild. I've never been next to an engine that
just fired so recently either man, this is crazy. So this will just be
basically boil off as the run lines upstream of the these
are the ISO valves here. So it's just boiling off and venting.
This is what I was talking about, like, hey, heat shield coming in, it's gonna, we're actually more worried that it's
gonna be cold instead of hot, right? Yeah, it's pretty cool.
You can imagine now! Hydrogen is absolutely the right answer
I think for our upper stage and what we're trying to do with it. But it is a little more
expensive from a you know, cost per perspective. It's a
little bit harder to source. And so when you think about rapid
turnaround and rapid reuse you know, the less you can use the
better. So that's one thing. And then the other thing, the
big thing is density, right? Hydrogen is just really, really low
density. So when you use it for a booster, the booster becomes huge. and, you know, physically large and
that's less optimal for quick reuse and operability perspective. So we use methane, it's about as cheap as you can
possibly get burns super clean and you know, I think it's the right answer
for rapid reuse booster engines. Yeah, but what about and, and then
the, the engine itself you know, you're using a more conventional set
of engines it looks like for your first stage. Yeah, so here's the thing. The, the weird, it's gonna be maybe
weird for me to say it, but an aerospike's is just not the
right answer for a booster engine. if you want high performance
out of the booster, the right answer to me is a
closed cycle booster engine. and, you know, you turn up chamber
pressure and make it operate, you know, that way. As you scale up aeros spikes, they they just don't, they don't
actually scale well. Right. Like you can't, the advantage of an aerospike would
be if you could get really high vacuum performance then maybe they would win, but they only get you what, 10,
15% mission average ISP benefit. Yeah. Something like that. And they want to be an open cycle just by moving it from an open cycle to
a closed cycle boom, you get that. Yeah. Yeah. Right. And then the
second thing is in vacuum, the higher performance comes
from a high expansion ratio. So you can get that with a regular bell
nozzle by turning up chamber pressure. In order to get it out of an aerospike, you have to make the
diameter this thing wider so. You can have a longer spike to work with. Well, so like the, the diameter of
the aerospike translates to the, the expansion expansion ratio.
Yeah. You know, the nozzle exit. Yep. Area, right? Yep. So to make it a higher expansion
ratio, you make it a higher diameter. but the expansion ratio is throat
area to exit diameter, right? Yep. So the throat area has to be the same
as you're making a wider diameter, which means if it's an annular,
annulus, annular throat. Yep. The throat gap is getting smaller
and smaller and smaller. Okay. Oh. So when you get to like,
reasonably big expansion ratio, so like even like a hundred,
150, 200, whatever it is, right? that, that throat gap is like literally
thrust thousandth of an inch. Tiny. So try imagining trying to
hold those tolerances in fab. And if you're off by a
thousandth of an inch, but your whole gap is like
three thousandths of an inch, then you have a massive thrust
imbalance from one side to the next. Whoa. So it doesn't make any sense. Right.
Right, right. So you're gonna, any, you're gonna ize these throats anyway
into circular thrusters like we have. Yep. They're gonna be all these
tiny little guys. it, it becomes like massively complex.
So Wow. It's kind of weird. We, we did wound up wind up with an
engine that uses the aerospike effect but is not designed like you
would see a classic aerospike. It's not like design, like, it's
not like you designed an air, you went out to make an aerospike
and that was your solution. It was more like your solution was reentry
and landing and then it's like, oh, I guess it's an aerospike now. The, yeah, I mean that's
exactly what it's right. We kind of started with the thesis
of the actively cooled heat shield. we thought about, you know, what that
vehicle looks like in that context. We wanted to come in base first
for various reasons partially cuz that makes sense for the
actively cooled heat shield. And we talked about the axial
load in both directions, you know, blah blah blah. So the major technical
problem for us was, alright, that all makes sense, but how do you bury a high performance
second stage engine into a heat shield? Yeah. And we went through all kinds of
different designs that were not aerospike. Yep. And finally wa landed on
this design that, again, it's not a classic aerospike, it does
make use of the aerospike effect, but. I love it! That that's how we
wound up. But yeah, not, doesn't make sense for the first stage. Can you run me through, like, just run me through the whole startup
process of either this engine or just a general engine? Cuz you obviously
worked on a handful of engines, so. Yep. Walk me through, make sure
I'm missing anything when I'm, when I'm talking about engine startup. Well I would say first of
all, the, first of all, globally the start transient
and to some extent also the shutdown transient are some of the
highest risk moments in a rocket engine. Right? And if you think about
it, like our little engine, a thousand horsepower in the pumps
bigger engines have tens of thousands of horsepower going through the pumps, and they go from zero
to full power in maybe a couple seconds, right? Yeah. So you've gotta control
all those horses and make sure they're running in the
right direction during that time. So in early development it is
usually one of the higher risk activities for rocket and engine. And then the actual transient
is pretty highly dependent on the engine cycle that
you're running, right? I would just say that, you know, as you're working through these
processes through development, here's a, there's cases where if
certain things are not right, like the pump is also
doing a lot of work, right? So one end of the pump turbine end
of the pump is generating power. Pump end of the pump is
consuming power. Right? Yeah. And we say a thousand
horsepower pump, by the way, one end is generating it and
the other end's consuming it. Yeah. So it's like, yeah,
it's all right there. It's like 2000 kind of plus a
thousand minus a thousand. Yeah. There's, so it's doing that
work. And if that's not balanced, if the amount of work you're asking the
pump to do outweighs the amount of power you're giving to the turbine, then yeah. It goes the other way and
doesn't bootstrap, right? Yeah. So you've gotta work through all
that and keep it all balanced. And then what's your actual. And by the way, it's also has
to happen on the oxygen side, and those two have to stay in balance
because they're coming together and joining in the combustion
chamber. So it's a dance. It is a, a very delicate
dance. And then how, what's your actual ignition process? What,
how do, how do you actually like the, the chambers? What's the, the process? There's a number of different
ways to light it, but you know, it's a fire triangle,
so you gotta oxidizer, you got fuel and you need a heat source. So you can get that heat source
through either a pyro solid, you know, propellant, you can get it through a
torch, you can get through a glow plug, get through a spark. so there's a number
of different ways we use one of those. Yep. and really trying to put that system
through the ringer also to make sure it's reliable. And one of the cool things that, I guess it's obvious
when you think about it, but every single test we're doing tests, 15 of these systems at
once we're racking up. Like if you rack up chamber
test time, we rack that up 15. 15 Times faster than a
normal, than a normal program! And that. It couldn't be seen as a totally bad
thing. But at the end of the day, it, it might be... At the end of the day, it's gotta
work, right? Like you look at Starship, it's got a gazillion engines, right? Yeah. And if you beat the crap
outta of these things enough, then you work all the bugs
out and they're reliable. Yeah. So they've gotta work anyway, that's true for accumulating test time. That's true for part to part
variability. That's true for you know, all kinds of stuff that,
that we see. And you know, this rework that we're doing
today is a, a great example. We just run as many tests as
possible and iterate and you know, fix the bugs as we go. That's so cool. so obviously, you
know, you guys using expander, you don't have, you don't have like
a, a preburner type of injector, so you really just have injectors in each
of the chambers here though you have a handful of injectors, 15 for now, 30 in the near future. Yep. Walk me
through like your injector choice solution. What, how do you end up
with, with what you ended up with? I guess the first thing
is that each of these, the way we control the vehicle,
we don't gimbal the engine. Right? It doesn't swing, which again, how do you fit a high performing upper
stage engine into a heat shield and make that robust? Yeah. We'd had, originally we were
gimbling it and you know, similar to the ceramic
tile question we had, when you get into a hot gas dynamic
seal that's reliable on flight 100, you know, we're just like, no, we're
never gonna trust that. So, right, right. so we designed out the gimbal and
the way we steer the vehicle is by basically individually throttling with
thrusters. So that feeds into, you know, kind of the rest of the design and, and you've gotta pick an injector
that's able to do that. Yeah. So we're using a pintle on these guys. It's it does a lot of
what we need it to do. And so that pintle is, can
be a source of throttling. And yeah, I mean it depends how
you design the pintle, but it's a, it's a good, it's a good
choice to design, you know, for a deep throttle injector. Because obviously the, the lunar lander engine used a pintle
injector and it allowed for quite deep throttling, if I recall. Yeah. And then one of the
nice things about it, and, and Merlin uses the same thing is you
know, you basically use face shutoff, which gives you a nice, very crisp
shutoff. And so one of the things, one of the downsides of this
architecture is when you think about shutoff, if you don't shut off one side
before the other or it's not crisp, then you get a moment and you're gonna
have to, it's not the end of the world, right. We'll have rcs on the whole
thing, we just correct it. But yeah, we do want a nice very clean
shutoff helps with insertion accuracy and other things you need
outta the upper stage. so yeah, the the pintle allows you to do that. Okay. Let's talk about
this a little bit too. Stoke will be steering the upper stage
both during ascent and during landing by using what's known as thrust differential. So instead of swiveling the
engines to steer a rocket, if you have multiple engines, you can increase or decrease the thrust
on one side of the rocket or the other to actually steer it. Now in Stoke's case, there aren't actually
multiple engines. Now, there'll eventually be 30 thrust chambers, but they're fed by a
single turbo pump system, which technically it one large engine. So they need to find a way to throttle
the individual thrust chambers. For this, you can use what's
called a pintle injector, which is not only in charge of the
mixing of the fuel in the oxidizer and combustion chamber, but a face shutoff pintle can actually
be used to throttle the engine. This is the same system that the Apollo
lunar module descent engine used to deep throttle. The pintle injector has the
advantage of maintaining the proper mixture ratios throughout
the throttle range, which helps make it very safe
and effective. And importantly, when you're dealing with
thrust differential control, your throttle actions need
to be quick and precise. Now, a turbo pump can often be too slow to
spool up and down for precise control, but stoke can operate their pump at a
relatively constant speed and bury the thrust individually on every single
chamber. And as Andy mentioned, it can also help ensure a nice
crisp shutdown too On the booster. Hey, where, where are you guys at
actually in that, in that process so far? Where, how far along are you. We're starting to build and test
hardware at the component level. Yep. So all of our component
facilities are over here. We've got two test turbo pump test cells. We've got our combustion devices test
cell finishing up component test cell for, for stage hardware. And I'm ready to go on that one too. Wow. Like what's your, what's your estimate for when you
hope to have a a completed first age engine? I think you'll see it come together
similar to the way Raptor came together, where we're gonna test a lot of, at the component level
and then we're gonna do, I guess what we're calling a breadboard
engine. They, they did one that was what was basically like a subscale
demonstrator based on, not based on, but similar to I guess
Merlin type hardware. Yep. We'll do similar style breadboard engine
as well and then we'll assemble it all into a real package. And it, and it's going to be, that's
going to be closed cycle. Is it. Closed cycle yep. Closed cycle, I assume.
Oxygen rich, closed cycle. Uhh... No we're gonna go all the
way. We're gonna do full flow. Are you serious? Yeah, I think, you know, look, our team, our team's got a lot of experience. any engine is hard and you
wanna build the thing in with the, the highest margin so that you
can run it over and over and over again. And I think. Wow. So you're hoping to be at
this point? I'm trying to think of, yeah, I mean that would be the third full
flow station budget cycle engine ever built. Oh, I guess the
third, the power head. There's the power power head demonstrator. Yeah. The IPD. Yep. So I guess kind of in a
way, the fourth you might be, and then the second engine to fly, leave
the testing. Cause there's the RD-270. Yep. The other is the power
head demonstrator, Raptor. Yep. And then you guys are going full flow! Going full flow. What the heck? Hang on, hang
on. They're they're going, they're going full flow baby. I mean this, so far this shirt's been fairly
representative of very few engines, but you guys are really, I mean. I mean this, we, we sat there
and debated this for a while, but what we're trying to do it's the right
answer. Every engine is hard. Yeah. And every engine's gonna take a
lot of investment and time and I think that, I'm not convinced
it's actually, if you design it, again, it all depends on design decisions, but you can design it where I think it's
not too much harder than anything else. Right. It can be harder. Yeah. Yeah. But it's also in a way
easier on, on a lot of the, the parts. Like it's. Yeah, that's the point. Especially like thermally through
the turbines and stuff like you. That's the point. Exactly. So in a way, you almost don't have to design quite
as and spend as much time doing insane, you know. You're not taking it up all the way to
the limit. Right. You don't have to. Right. You have that, that inherent margin built in and
then over time you can upgrade, up thrust and you know, things like that. And you have that margin
to be able to do that. So That's so cool. Oh, well
that's gonna be amazing. Well, thank you so much for your,
all your time. I mean, this has just been amazing and
everything you're working on, it's gotten me as you can tell.
Very excited. I, this is awesome. This is really, really cool. I thank you for letting us like share
what you guys are working on with the world. It's, it's amazing. Yeah! And thanks for coming out and
you know, helping us tell the story. Yeah, it's my pleasure,
really is my pleasure. Thanks so much to everyone at Stokes
Space and especially Andy for all of his valuable time and for letting
Ryan Chylinski and I come
out here and film this interview and engine test. It was absolutely a dream come
true and I am so excited to watch this company continue
to develop their system, but I also owe a huge thanks to my Patreon
supporters for helping make content like this possible. If you wanna
help me continue to do what I do, head on over to
patreon.com/everydayastronaut,
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everybody. That's gonna do it for me. I'm Tim Dodd, the Everyday Astronaut bringing space
down to earth for everyday people.
