- Hi, it's me, Tim Dodd,
the Everyday Astronaut.
So, just the other day, SpaceX experienced
a failed landing attempt
of their Falcon 9 rocket.
And this was a brand-new Block 5 booster,
it had never flown
before, it was B1050.1.1,
means it was the first flight of it.
I talked about it just the
other day on Wednesday,
I have a video out.
Click here if you need to see that first.
But it talks about kind
of just an overview
of what happened.
But that video still led
to a lot of questions
about how did it end up
in the ocean, you know.
Why didn't it crash down on LZ1?
What kind of control did the
Falcon 9 still have, you know?
You can see it fighting for stuff.
How much control does it actually have
when it experienced the
failure of the grid fins?
And then, of course, like
you know, was it safe?
All this stuff, and actually,
talking about safety,
we're not gonna really
dive super deep into, like,
the automatic Flight Termination System
or Flight Termination today.
We'll touch on that for just a second,
but I'm really excited to show
you what I've got going here.
So, I'm gonna first show
you the exact trajectory
that it's supposed to take.
We're gonna dive into how
it would normally fly,
what these return to launch
site missions look like,
what the landing process
looks like with this,
and then I was able to
exactly replicate this
in Kerbal Space Program, like to a T.
It's pretty crazy.
So, I'm gonna show you
exactly what a normal return
to launch site landing look
like and then I'm gonna show you
what the ballistic
trajectory would look like
if the vehicle had, like, shut off
mid-falling back to Earth,
and then I'm gonna
replicate the exact failure,
and it's absolutely
astonishing how close it is.
So, let's dive right in here.
First off, this is my friend Declan Murphy
and he has his website
called flightclub.io.
And I'm a huge fan of this website.
It's incredible.
He made this simulation software.
I support him on Patreon
because this work is incredible.
I don't know how he does it.
I highly recommend, if
you find as much value
out of this as I do,
hop on over to Patreon
and support Declan because
this is, get ready,
your mind is about to be blown.
Here we go.
Boom!
Data!
Now, what is this?
I mean, just looking at this,
even to someone like me,
I kind of understand some of this,
but it's still like really
hard to grasp what's going on
and Declan, man, you're
an absolute genius.
What are you, how did you, what?
How do you do this?
Okay.
So, I don't...
This is cool.
That's great, Declan, good job,
but this is the part that blows my mind.
You can click on 3D Visualization
and we can actually pull
up the exact trajectories
plotted against Google Earth.
Look at this.
So, he goes through and he, I mean,
I don't know how you do this
other than just being some
kind of mad scientist.
Okay, so look at this.
So, it doesn't look like
much now but loooook, boom!
You can see the exact flight
path, an exact trajectory
of what was supposed to
happen, and for the most part,
what really did happen in this mission.
So, here you can see
there's a red line going up
and then it goes blue,
and then it splits off
into two red lines, there's a blue,
red line falling back down,
a red line and a blue line.
So, red line means an engine is firing,
at least one engine is firing.
It means it's accelerating.
So, you can see here the
first stage accelerates
for about 2 1/2 minutes and
then it does that coast phase
where it stayed separating,
and then the second stage ignites, whoook,
and it continues off into orbit,
and you can see that just perfectly here.
Look at that.
Declan, man, this is such
a great visualization.
I just love it.
But, now the first
stage, on the other hand,
does that boost back burn.
So, we can see it lighting
up, the two lines split apart.
The first stage starts to kind
off fly retrograde almost,
it's trying to point
itself back towards land.
It's not pointing itself at land actually,
it's pointing itself just short of land.
And what's gonna happen
is, you know, of course,
now the upper stage and
the payload is detached
so the vehicle doesn't have
nearly as much work to do
on the way back down as
it did on the way up.
It's burned through like 70% of its fuel.
It's a lot lighter.
It takes a lot less to slow it down,
and now the atmosphere is working with it.
So, in order to land, it
doesn't require nearly
as much energy as it did to get up.
And, of course, you can
think of this upper stage
as almost like the first stage
is hucking the upper stage
towards orbit,
then once it's up high
and moving really quickly
towards this direction of travel,
the upper stage puts itself into orbit.
It does like another 6
1/2 minute burn or so,
and then that's how it gets into orbit.
Meanwhile, the first stage,
though, comes falling back down.
You can see there's a red line.
That's going to be the entry burn.
I still think it's the reentry burn.
SpaceX used to call it the reentry burn.
Now they switched it to entry.
The vehicle was in the atmosphere,
leaves the atmosphere, and comes back in.
To me, that is a reentry, not an entry.
So that's the reentry burn you see here,
and it does that to slow itself down
before it hits the atmosphere
so the atmosphere doesn't destroy it.
And then you can see a
little bit of a kink in this,
and that, my friends,
is the dogleg maneuver.
So notice it's a blue line.
That means it's coasting, so
the propulsive landing stops,
and all the sudden, you
see it start to kink over.
So if the vehicle after the reentry burn
or even before the
reentry burn were to fail
and totally shut off, it
would fall straight down.
It wouldn't have this dogleg.
This dogleg is due to those grid fins
starting to bite into the atmosphere
and starting to tilt the vehicle over
and aim it back towards land.
We have really good footage of this.
I think my favorite
footage is from NROL-76.
That was in 2017, and you can just tell.
You can see how much the
vehicle is doing this dogleg
and how much it kind of can almost fly
through the atmosphere.
It's really, really cool,
and it needs the grid fins
to do this, so if there's
a failure in the grid fins
or a failure in some other system,
it's just gonna go, boop, right down,
following its ballistic trajectory.
It's these grid fins, and you know,
a little bit of the
nitrogen thrusters too,
that help point it towards LZ1.
Okay now, while we have this pulled up,
it's probably a good time
to really quickly touch
on the automatic Flight Termination System
or the Flight Termination
System, and what this is,
is any rocket that flies and
any rocket that has flown
almost ever, has a
Flight Termination System
that's typically watched over
by a range safety officer,
someone literally with
their hand on a button.
And they watch the trajectory,
and they watch the actual
telemetry of the rocket,
and if it leaves a
predefined flight corridor,
they make sure, like, you
know, if at this point,
it turns and goes this
way, boom, you know,
nowadays it's automatic, and
if it automatically exceeds
that certain corridor
or basically like a cone
of where it should be going,
it will blow itself up.
And that's true on descent as well.
So say that boost back
burn would go too long
and all the sudden it
gets beyond what's safe,
as soon as it crosses that
threshold of, like, oop,
you shouldn't have burned
for that extra three seconds,
boom, it will trigger,
and it will release all
of the extra propellant
that's on board and explode.
It will completely get rid of that.
That's a lot of energy there.
So it's a lot safer to
ignite a rocket in the air,
purposefully self-destruct it,
get rid of all of the combustibles,
the high-energy combustibles,
before it impacts the ground.
'Cause if a rocket impacts
the ground full of propellant,
that's bad.
That's very bad.
That will throw shrapnel and shock waves
and a ton of energy, and
be a very, very bad thing.
But meanwhile, if you
do it in the atmosphere,
in the upper atmosphere,
it kind of breaks apart,
gets rid of all the propellant,
and it just kind of will rain
small bits of shrapnel down.
I know it's not a great consolation,
but it's really not nearly as dangerous.
And if you like watching rockets go boom,
you're kind of sick, but I get it.
It's a bit of a morbid curiosity.
I do have a video
called Biggest Booms of
Space Flight History,
and we do explain what went wrong
in all of these different
explosions with rockets.
I love that video.
It was a lot of fun.
Definitely check that out
if you want to see more about this.
There's a link here.
There's a link in the description.
Okay, but back to the Falcon 9,
and specifically when it's
doing like, a boost back burn.
You know, it physically, if it
were to do a boost back burn
for slightly too long,
it would get terminated.
It's not going to go too far
and all the sudden be over Titusville
or you know, over Kennedy Space Center.
It would get terminated
before that happens.
So as soon as it crosses
that certain threshold
where it's like, oop,
you're accelerating
towards populated areas
or onto Cape Canaveral Air
Force Station or something,
it gets terminated before it does that.
So that being said, the
last opportunity, really,
the Falcon 9 has on its way down
that could potentially
throw it toward something
is that reentry burn.
So the reentry burn, once
it does this reentry burn,
you'll hear them call out on the radio.
You might be able to catch it.
I know you can catch
it on the SSOA mission
that was just two days before CRS-16.
You hear them make a clear call-out
that the first stage booster
Flight Termination System
is safed.
- [Woman] Will happen
followed by a touchdown.
- [Man] Stage one FTS has safed.
- And that's because after
it does that reentry burn,
that's kind of the last time where, say,
it came at a super weird angle and, phew,
started to shoot off towards the horizon.
It would need to be able
to self-destruct itself.
After that point, though,
it's already coming so close
to the ground, the actual, like, area
of where it could impact
is a pretty small cone.
It physically can't go that
far, you know what I mean?
So you'll see more of this play out here
in Kerbel Space Program.
You'll see more of it here.
Let's fire this up in
Kerbel Space Program,
and let's actually dive into this.
It's crazy how similar it actually is.
Okay, so what I did is I
actually created a mission
using Kerbal Space
Program's mission simulator.
And look, actually, I
placed us right here.
This would be as if we had
just done the boost back burn,
and we're beginning to fall back to earth.
Now, this makes it so that
we're purposefully going to fall
just short of the land,
and this is very similar
to the actual trajectory that
the Falcon 9 booster takes.
And so look, from here,
it almost looks like
we're going to fall short
initially, and we kind of would,
and what I'm going to do here, though,
let's fast forward quick,
and we're going to get
to the entry burn here.
Okay, so I'm actually going
to be manually flying this,
but I'm gonna hit the same
numbers every time I do this
just so we have something.
So at 60,000 meters, boom,
we light up three of
the nine Merlin engines,
and we intentionally are...
I'm actually burning,
just holding straight down
instead of exactly retrograde.
This makes it so that we still keep some
of that horizontal velocity
that we're going to need.
We're gonna need to increase
that horizontal velocity
so we can do that dogleg,
so I'm slowing down
before we really hit the
atmosphere here in Kerbal.
And you can tell I'm gonna
stop at 400 is the number
that I stopped.
It seemed on this mission
to scrub off about 2/3
of its velocity on the way down
before it hit the atmosphere.
So this is just kind of a rough estimate.
Again, I just wanted to
make sure we had numbers
we could replicate over and over.
And now at this point,
I'm gonna tip it over,
and I'm gonna start trying to fly it.
Now, this is the cool part.
This is the dogleg.
And from here, it looks
like it's, you know, crazy,
crazy steep.
It's really only, you
know, a couple degrees
off of its angle of attack.
Yet you're gonna start seeing
as the atmosphere gets thicker
it's unbelievable how much
you can actually dogleg over,
and this is about exactly
what the Falcon 9 does.
Now Kerbal, to get the
physics kind of close,
especially with like,
I'm using the space shuttle
main engines to use just one.
The vehicle needs to have a
little bit more aerodynamic bite
and this is all stock physics
in Kerbal Space Program.
So in order to make it
fly a little bit better,
there's a few wings
hidden inside the fuselage
so that the fuselage has
the right amount of lift.
There's also some air brakes
to help increase the drag
on the vehicle
just to make it so we
can simulate this closer
to how the Falcon 9 actually functions,
because that body, the fuselage
actually has a lot of lift.
Now, this is where I began the entry burn,
and in this case, I
scrubbed off a little bit
of extra vertical velocity
by kind of using that engine gimbal
to tilt it a little bit more,
but now I'm just following the retrograde.
I'm following the exact trajectory,
and that way it'll scrub
off the horizontal velocity,
but it's also scrubbing off the falling,
the vertical velocity.
And I'm just eyeballing this.
I'm kind of taking a look
at there's the suicide burn
distance calculator up there
in the top right.
Even though it's negative right now,
you need it to be a little bit negative
because it shoots up
and down all the time,
especially as the atmosphere changes.
It's not the most accurate
thing in the world,
but now I'm just giving it full beans,
letting the landing gear
come out, and viola.
We're about to have a pretty
decent touchdown there.
Look at that.
And now you can kind of see
there's a fly around here.
You can tell about how far we made it in.
We made it lined up with the
big markers on the runway
that far inland.
Good enough, I think, as far
as Kerbal Space Program goes.
So next, let's actually take this thing
and do that exact same flight path again.
Since it's the mission simulator,
I actually did a quick save,
and we're gonna turn off.
After the entry burner,
we're gonna turn off all stability control
and see what happens
when it just follows its
ballistic trajectory.
Okay, so just like before,
I did the entry burner
starting at 60,000 meters,
and I'm gonna slow it down
to about 400 meters per second,
and at that point, I'll kill the engines,
and then I'm actually just
gonna kill everything else.
I'm gonna turn off stability
control, turn off RCS.
This would be like if, you know,
a major, major malfunction happened.
Where is the booster
going to end up, you know?
And this is pretty accurate, you know?
So the grid fins would
freeze at this point.
But even up here, the grid fins
don't have that much attack.
They don't have that much control,
so currently they are locked into
just the dead zero position.
They are zeroed out,
and watch what happens.
There's SAS off; there's
no more nitrogen thrusters.
This is a dead.
It's almost like the
batteries got disconnected
or something.
This is a dead rocket,
and where do you think
this is going to end up?
This is actually pretty surprising,
'cause notice due to the grid
fins having a decent amount
of atmospheric drag
and because the engines
and the bottom portion of
the booster is the heaviest,
the center of mass is very low.
The center of lift is really high.
The center of lift is
up at those grid fins,
and so it wants to almost stay
following the retrograde
marker here, you can see.
So it's still actually kind of, you know,
heading towards land.
It's not like it drops straight down.
It's going to follow a little bit
of that horizontal drag over,
which means it's still
going to kind of creep
towards Kerbal Space Center in this case.
But it's gonna come up short of the land.
It's gonna come up
significantly short of land,
and that just shows how
much those grid fins can do
that dogleg maneuver, pop it over to land,
and now you just see, it's
gonna have a little swim.
And in this particular
flight, you can tell.
Look at how fast it's going.
So this is terminal velocity.
It's just a pencil falling out of the sky,
a 15 story tall pencil.
(splash)
There it goes.
Nice little dunk in the ocean.
Bye, bye.
That's the worst case scenario,
at least as far as the final
landing, all the maneuvering.
So here is what would happen.
So what I did is I went back
into the vehicle assembly building,
and I'm intentionally
going to make it wonky.
So what I'm doing is I'm
taking pairs of grid fins,
and I'm going to kind of make
them sporadically different
because the grid fins can all act together
if they all move on the same,
like, you know, like this.
That's gonna induce roll
throughout the whole vehicle.
If all four of them are
doing that same thing.
But sometimes they act
symmetrically like this.
In that case, it either
can produce pitch or yaw.
So if they all work in unison
like this, that's actually unison.
It's not mirrored.
That's how you induce roll, but
you can induce pitch or yaw.
So two of these are
stuck in a yaw position,
and two of them are
stuck in a roll position.
So you can see two are the
same and two are opposite
of each other, and I'm
just kind of guessing
that that's the failure we saw
because basically what happened,
because the pump that controls
the grid fins turned off,
it had a malfunction, it shut down,
they were stuck wherever they were.
So if at the time the computer was saying,
"Hey, you need to point
yourself this way,"
you know, two of them
could have been starting
to work on some yaw or pitch,
and two of them could have been
doing a little bit of roll.
And then especially as it
started to roll a little bit
out of control, all of
the sudden, you know,
they kind of cranked over at one point,
and then it just locked there.
And so what my best understanding
is of this entire system
is initially through the reentry burn,
through the boost back burn
and then the reentry burn,
it's kind of almost slowly
creeping closer to land.
And after the reentry burn, it retargets
and really then does aim to land on LZ1.
But I don't think it's like, you know,
I don't think it's totally dynamic.
Like, it's not necessarily
saying at any point.
Like, it can't relight the engines again
if it came up short the
first time, you know,
or anything like that.
So I think the boost back
burn targets a certain thing,
then it kind of does some
fine-tune adjustments
with the RCS and the atmosphere.
You can kind of see that sometimes.
And then once it does the entry burn,
it kind of sets the target again,
and it changes its target
now to be the landing zone.
So either Landing Zone One
or in the case of a
ballistic trajectory landing
out of the drone ship, it targets itself
to now retarget that because
I think they intentionally,
especially with these
return-to-launch-site landings,
intentionally initially target short
so that if, you know, anything goes wrong,
it does what we're gonna see here.
So again, I did that same 60,000 meter
burn.
That's where I started the entry burn.
I'm gonna cut it off at 400
meters per second in velocity.
That scrubs off about 2/3 of our velocity.
And now the grid fins, I
actually turned off the ability
for them to move so they're
stuck in this launching position
but here's the thing.
The rest of the vehicle still has control.
So the RCS, the little
control thrusters at the top
of the booster still have
the same amount of control.
The gimbaling of the engine
still has the same amount
of control, and it's going
to still try to point.
Notice it's trying to
point itself at land.
And I'm also holding the
stick, trying to induce more
of that pitch to let it
do more of the flying,
just like the computer would.
The flight computer is trying
to target it, you know.
You can actually think of it,
although this is probably
not the nicest thing to say,
but it is basically a ballistic missile.
It's a missile falling out of the sky,
and it is now setting its target to LZ1.
But now notice we don't
have control over it
'cause those grid fins are stuck,
and we're starting to get in this spin.
And occasionally you'll see
kind of wild oscillations even
because some of those grid fins are stuck
in other positions.
But now watch.
It's gonna actually start
getting tighter and tighter
and tighter, and I ended up
going as the engine's going.
So now the engine fires up,
so the engine gimbal has some control now,
but it's a single engine gimbal.
A single engine does
not have roll control.
It takes at least a pair of engines
in order to induce roll
through the Z axis of a rocket.
So if you have two engines,
you can spin them opposite like this,
and that will make the rocket spin,
but the landing burn on
this mission in particular
and on most return-to-launch-site missions
is a single landing burn.
These are when you have
enough margins, it's easier.
There's a lot more wiggle
room in these landings
when you have room to do
a single landing burn.
It's a more aggressive
suicide burn or hover slam
when you try to do the
three engine landing burns.
So this mission was a single landing burn,
so that means the center engine
didn't actually have control.
Now look at this.
This is almost exactly what
we see with the videos we saw
from land, you know.
Again, my friend Das Valdez had that video
and then SpaceX released
the video, and in real life,
when the landing legs came out,
it killed virtually all of the roll
due to the conservation
of angular momentum.
So just like an ice skater,
you know, and voila.
You see mine broke apart, boo.
Boo, Tim, you don't make good rockets.
SpaceX makes way better rockets.
But that's actually pretty
amazing that the booster survived
tipping over like that.
Mine wasn't quite so fortunate.
Poop.
But back to angular momentum,
so one of the landing legs deployed.
You know, just like if, you
know, you see ice skaters,
and they can slow their spin
down and then speed it up
by bringing their arms in or
if you're on a chair like I am.
I'm not gonna do it right now,
but if you were spinning really
quick with your arms tight
and then you extent your
arms, you slow way, way down.
Like, you can almost stop,
and I think that's exactly
what happened with this booster
once those landing legs deployed.
You can see all of the Z axis
roll basically canceled out
instantly, and people
were saying, you know,
"Is it because it's going slower
"and the grid fins don't
have much control?"
I don't really agree with that because
watch some of the F9R dev
or the grasshopper launches
that SpaceX used to do
when they were learning
how to do kind of the landing burns.
They're going really, really slow,
and they pop out kind of their
first generation grid fins,
and you can see even going,
like, not even at all fast,
like really slow, like a crawl,
how much roll they can
induce with those grid fins.
So I don't think it was a matter
of the air speed was low enough
'cause the air's really thick down there.
Those grid fins have an
insane amount of control.
They're basically like the elevators
and the rudder of a plane.
They can at that speed still do a lot.
So I don't think it's that, you know,
the grid fins were going slow enough
that it killed off the roll.
I think it's more that the conservation
of angular momentum with
the landing legs deployed
and therefore it stopped rolling
just as it was about to touch down.
So
to sum up,
really the booster had virtually no chance
of making it back to land
because the mechanism that
mainly gets it over land
are those grid fins.
So if those grid fins fail, you know,
if they're locked out like
they were in this case,
it's gonna fall basically straight down.
Now of course that brings
up the question, like,
what if they're jammed and
it flies, you know, way off?
It really probably no
matter how jammed they are
in no matter what configuration,
it probably physically
cannot fly much beyond LZ1.
I'm sure there's a reason why
they have that aggressive dogleg maneuver,
and I'm sure there's a reason why
they point it just short of LZ1.
I'm guessing that even in
the worst case scenario,
it could maybe fly in another
kilometer or something.
Hans mentioned that it knows
not to target buildings
and things.
It knows were those are.
But in this case with the
little amount of control
that the vehicle actually
had at this point,
the safest thing for, you know, it to do
is in the ballistic trajectory
that they programed in,
they made it so if there is a failure,
it almost no matter what's going to fall
where it's going to fall.
So although yes, I'm sure
the vehicle is smart enough
to know where it is
and try not to hit the
vehicle assembly building
or something like that, at the same time,
it's pretty much destined to
follow its ballistic trajectory
at that point because
there's not that much
it can actually do.
The most it can do is make it over to LZ1.
Maybe a little beyond, you know,
margin of error type of
thing, but I don't think
it can all the sudden whoa,
and it's gonna shoot off
and oh, no, Cocoa.
Cocoa's now gone.
Titusville, I loved you.
I don't think it has even the
remote ability to do that,
and that's not necessarily
again thanks to the flight
of the vehicle and the flight control.
That's more due to the programming
of where it initially targets,
and then it's retargeting towards land.
Again, that's just kind of me speculating.
If you guys have more input
on this or more questions,
please let me know in the comments below.
I am very curious.
We still have questions
to answer, like, you know,
now they are talking about
maybe adding a redundant pump.
What's that do as far
as their certifications
for NASA to fly humans?
Will that affect the
certification program?
It sounds like this was the second flight
with the upgraded COPV's.
I didn't know about that.
That's awesome.
They need seven flights of a frozen design
in order to fly humans, according to NASA.
So SpaceX is very prone
to tweaking constantly,
so NASA kind of was like,
"Hey, you guys need to
stop tweaking for a bit.
"Make sure you have a solid rocket."
And as far as the customer goes,
as far as NASA's concerned,
this mission was a complete success.
They don't care if SpaceX
doesn't land the rocket.
That's not anything to do with NASA.
That's in SpaceX's best interests.
So what NASA paid for was
to get the Dragon capsule
to the international space station,
which it's on its way doing now.
The landing is really only advantageous
and really only matters to SpaceX
because they want to reuse that booster.
So it's really the financial
case of oh, here we go.
So all in all, again, to sum up,
we still don't know about that.
And I'm excited to see what that's like,
and the other thing that I'm surprised.
This is again just me
speaking very openly.
I am surprised that this
is the failure we saw.
That we saw a failure of the grid fins.
I always thought that I
was nervous for the day
that one of the engines doesn't light up
because that is a one shot thing.
You know, when you're coming in that fast,
if the center engine doesn't light up,
and you're doing a single
engine landing burn,
you're screwed, and I don't
know what kind of backups
and processes they have to make sure that
that TEA-TEB is able to ignite the engine
in the last second.
I don't know, but if I were
to, you know, place a bet
on what failure we'd see
for a landing of a Falcon 9,
I thought it would have been the engines.
The grid fins, titanium, you're
beautiful, and I love you,
and I'm excited to see that hopefully now,
they will get them fixed,
so I hope this answers all your questions.
Again, let me know if you
have any other questions.
Sorry for rambling so long.
I just figure I'd just kind of
openly talk about this stuff
because it's cool, and again,
it's one of those fun
opportunities to watch
and learn together, and that's
always fun in my opinion.
So yeah, thanks for my Discord channel
for chatting through this with me.
It's been a lot of fun.
If you want to join our
exclusive Discord channel,
please head on over to
patreon.com/everydayastronaut.
And again, all the music
in my videos is original.
I finally released an album
called Maximum Aerodynamic Pressure
that's available everywhere,
iTunes, Spotify, check it out.
It's been in the background
of this video the whole time,
so if you like it, download it.
There's also a playlist here on YouTube
that you can listen to.
It's pretty chill background
music, so all right, everybody.
That's gonna do it for me.
I'm Tim Dodd, the Everyday Astronaut.
Talking grid fins with you here today.
Bringing grid fins to
earth just like CRS-16.
All right, bye, guys.
(relaxed music)
