- 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)
TLDW on the why no terminate:
Autonomous flight termination was already off at the point control was lost, and it was off because from that point onward, in case of failure the booster would still always land/hit within the safety areas. Single rocket hitting somewhere inside designated safe zone is preferable to a cloud of small bits in the same area which is far bigger job to clean up. Trajectory is designed so that the booster requires active working control (both engine and grid fins) to reach the pad and literally cannot hit land if control is lost before landing burn.
...and it all worked exactly as planned. Even without grid fin control, the booster stayed well within safe areas and even managed a soft touchdown as a surprise bonus.
Looking at the landing, I noticed that the rocket tilted itself a large amount late in the landing burn. Could this have been to control rotation? When you take an object spinning in one axis and force it to turn in a second axis, some of the rotational inertia is shifted to the third axis. The rocket engine couldn't do anything about the rocket's spin, but a trick like this could shift some of the rotation to an axis that the engine could do something about.
I believe that the rocket's control system does use an aerodynamic model to decide how to control it, and such a model could come up with such a trick to control what it was unable too.
My question is why it attempts a landing burn even though itβs aborted the landing. Best guess is itβs easier to investigate the failure when the rocket isnβt completely destroyed. Also, they want a chance to salvage parts.
I'm not shure but I think there is an error in this video: At 14:49: I don't think the center of lift is at the grid fins. The center of lift must be where the center of mass is, otherwise the rocket would spin around it`s pitch axis. The fins are actually the equivalent of the horizontal stabilizers and elevators on a plane, while the rocket is basically a bad lifting body creating lift.ο»Ώ
Acronyms, initialisms, abbreviations, contractions, and other phrases which expand to something larger, that I've seen in this thread:
Decronym is a community product of r/SpaceX, implemented by request
8 acronyms in this thread; the most compressed thread commented on today has 82 acronyms.
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