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For the first time we have the means to fully explain how and why SpaceX will try to catch the largest rocket ever built out of midair.
My name is Felix, and I am your host for today’s episode of What about it!?
And as always, there’s been a lot going on in the space industry lately, so let’s dive right in!
Why take the risk?
This time it‘s all about the truth.
Since Elon Musk and SpaceX announced the idea of planning to catch Starships and Super Heavy boosters out of midair,
the Space enthusiast world has been wondering and speculating, how exactly it will happen.
Now, Elon Musk has unveiled the first real and hard data which for the first time gives us the means to fully explain,
how exactly a Mechazilla catch works and why the heck SpaceX is daring so much in the first place!
Why risk it all to perform the largest Party trick ever?
Let’s dive right in!
The real deal. Directly from SpaceX’s internal simulations.
We have all the data now. Body acceleration and body rates on XYZ and the corresponding altitude.
Suppose you’re not familiar with the XYZ coordinate system, it is a way of precisely showing a position in a 3-dimensional space.
Also referred to as the Cartesian coordinate system it shows x and y as the position on a plane and z referring to the height.
And Musk didn’t just show the movement from directly above Mechazilla, but all the way from the beginning of the final landing burn.
So, the first exciting thing to note here is that the landing burn starts at roughly 1800 meters above Mechazilla.
Back on Episode 200 I compared Super Heavy with a Falcon 9 booster.
So, let’s take a look, at which point a Falcon 9 booster starts that reentry burn.
There you go. 1800 meters. So, it’s almost exactly the same as what’s planned for Super Heavy.
Same tech, same results. Super Heavy basically is a Falcon 9 on steroids.
We can also see that the booster very much comes in at an angle.
This is likely due to the fact that SpaceX will do a so-called dogleg maneuver to protect Orbital Launch mount and Mechazilla,
if something goes wrong in the early approach phase and to use as much lift from the booster’s body as possible to further slowdown the descend
as can be seen in an official SpaceX graphic depicting a Falcon 9 launch and landing.
Aerodynamic guidance. Grid fins steer lift produced by first stage.
Again. SpaceX wants to do exactly the same thing as they do with Falcon 9 boosters right now.
Then, at around 800 to 700 meters above the pad the booster switches from using all 13 center engines down to only three,
which creates the huge bump in the body acceleration graph.
Since there’s an engine shut down the TVC of the remaining three engines has to fight to keep the booster on track.
The same can for example be seen on every High-altitude Starship Flight test.
It doesn’t matter if the rocket is going up or down.
When ever an engine shuts down,
the remaining ones have to compensate for the sudden change in thrust with their thrust vector control or TVC, also called engine gimbal.
Raptor engines have clearly demonstrated, that the current avionics and TVC hydraulics can do it on Starship flights.
This is also the point at which the booster becomes too slow to produce any meaningful lift and so it turns its engine section straight down
as it positions itself above the Mechazilla Chopsticks.
I cannot wait to see this in reality.
Even watching this simple animation get’s my heart rate up!
Shedding more and more velocity using the three remaining Raptor engines on final approach,
the booster carefully positions itself right in the middle of the chopsticks and with its grid fins pointing left and right.
Ryan Hansen Space released a spectacularly detailed animation just two days ago.
He worked together with Owe from SpaceX 3D Creation eccentric and showcased how SpaceX will be lifting booster 4 onto the orbital launch mount
utilizing the Mechazilla chopsticks.
Now, this animation is not about landing,
but it does show the Chopstick mechanics like no other animation before and those are the same no matter if you lift or catch a booster.
This is what I want to point out.
The booster will come to rest on the Chopsticks with these little arms or anchors here.
And those are positioned in the middle of and directly under the grid fins on either side of the boosters hull.
So, it will be absolutely vital for the booster to come down with the grid fins oriented towards the chopsticks on both sides.
But again, we do have something to compare Super Heavy to.
Falcon 9. So, is SpaceX capable of controlling the rotational movement of their boosters on descent?
Here we go. One of the best landing footages ever presented by SpaceX.
Saocom 1B from October 8th of last year.
Uninterrupted footage all the way from Space to LZ1 at Kennedy Space Center.
And at the very end, just meters above the pad we can see rotational movement, still we can also see, that this very much seems to be under control.
The booster can rotate back and forth and on the final meters it doesn’t rotate at all.
This is because the rotational movement should be relatively easy to control using grid the grid fins.
And since Super Heavy will be using exactly the same system, it should be precisely the same process, in theory.
And if it is not in the absolutely perfect position, Mechazilla already has a system in place to tolerate a few degrees off the rotational axis.
Owe from SpaceX 3D Creation Eccentric has made a great animation to show how this will work.
Pushers close in on the booster after the catch and guide it on both sides to that perfect center position to be able to precisely place it on
the Orbital launch mount again.
Rapid reusability.
SpaceX has one huge advantage.
They already know about all this.
After 101 landings of an orbital class rocket booster they’re still the only launch provider in the world to possess this know how.
And it’s precisely as predicted on Episode 200 and 10 days ago.
In theory, the chopsticks wouldn’t have to move much up or down at all during the catch.
It is not a crazy agile robotic arm, moving along with the booster’s path for several reasons.
The orbital launch integration tower or Mechazilla is enormous.
The Chopsticks alone likely weight around 100 tons each.
Even though the Drawworks used to move them up and down has 6000 horsepower,
the inertia of such a heavy setup alone would be enough to stress the cable connection between winch and chopsticks immensely if it were to move abruptly. And last but not least,
Falcon 9 doesn’t need the drone ship to have any sort of dampening besides the honeycomb crush blocks inside the Falcon legs.
These are the legs of a Falcon 9 booster after a landing and as you can see, there is a measurement on the lowest point of the leg dampeners.
That is there, because there is a honeycomb crush block inside those legs,
dampening the landing each time a Falcon 9 sets down on a drone ship or at the Landing Zones at the Cape.
These Crush blocks are non-reusable and require SpaceX to refurbish the legs each time a booster has landed.
For a Starship or a Super Heavy that’s not an option as there simply are no legs.
So, what does SpaceX do instead of moving the Mechazilla arms down to dampen that last bit of vertical movement?
The bars to work as the landing surface for the boosters catch points is movable.
Up and down. It’s not much, but the travel distance is comparable to what a Falcon 9 leg solves with its crush block.
This is not confirmed yet, but this might be that last puzzle piece that we’re still missing.
That last bit all the way from Space down to Z+0 that really needs to be as soft as possible.
It's not much at all. Just a few centimeters in theory.
That’s all that’s needed from 100 kilometers above the planet down to the resting position.
If that last tiny bit is soft, it would work.
Is that all it takes? What’s your thought?
As always, tell me in the comments!
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Jumping back into our Booster catch simulation directly from Elon’s development team, let’s take another look at the very last part of the catch.
Notice how long the booster hovers in the air.
That’s at least 5 seconds of hovering.
It’s not a suicide burn like what we’re used to seeing on a Falcon 9 landing.
Every Falcon 9 booster uses the same technique to achieve zero velocity.
It’s called a suicide burn. SpaceX does this for two reasons.
One being fuel consumption. If you do a suicide burn you use as little fuel for the landing as possible as hovering basically is wasted energy.
Secondly a Merlin 1D engine, as used on a Falcon 9 booster, has too much thrust and by design can’t throttle down enough.
The booster itself is so light before touch down, as it’s tanks are almost completely empty that a Falcon 9 can’t hover.
If the engine would continue its burn, the booster would come to a stand still and then start going up again.
Even when completely empty, a SpaceX Super Heavy Booster weighs far more than a Falcon 9 booster [correction: ~22t].
Around 200 tons. The minimum throttle range of a Raptor engine will likely be somewhere around 40% of its total thrust. [F9 booster mass correction: ~22t]
From Elon Musk we already know that currently the thrust should be at around 220 tons when running at 300 bar chamber pressure.
40% of that would be 88 tons.
Times three we’d be at 264 tons.
A bit too high, but SpaceX could in theory shut down two additional engines and do the hover with one engine,
which would be risky or the throttle range of a Raptor 2 is even lower than 40%, which would make the trick work as well.
Either way, the simulation shows us that Super Heavy can hovering and that SpaceX intends to use it too.
Very much in a similar way to what New Shepard from Blue origin does before touching down.
Hopefully with less sideways movement involved and with a much larger booster, but at least comparable.
As a final move, the chopsticks move inwards, maybe even slightly pushing the booster and grabbing it.
That’s it. Booster caught.
Then the mentioned alignment system kicks in, centering the booster in the perfect position.
Now here’s what I talked about in the beginning.
There’s one question I hear a lot from you.
Why risk it? Why not just build legs and land it normally?
Why risk all this in the first place,
build a complicated Mechazilla and enter completely uncharted and new territory with the largest rocket ever built by trying to catch it out of midair?
It’s a valid question. Legs would certainly be easier.
To answer the question, we have to look at the main goals of the Starship launch system.
Full reusability and rapid reusability.
As we discussed earlier in this episode, full reusability is hard to achieve with legs.
It’s the rocket, doing the landing on its own.
It’s the legs taking the beating and they need to be checked and parts need to be replaced on every landing.
So, getting rid of the legs altogether is one possible solution.
But in theory, you could come up with a leg design that doesn’t need checking after every flight.
A leg that doesn’t need crush blocks or maintenance.
So, what about the second reason?
Rapid reusability.
By landing the booster and later even the Starship itself on the chopsticks and by catching it with Mechazilla,
the Super Heavy Booster and the Starship are instantly back in the launch process pipeline.
Mechazilla can just lower it back down onto the orbital launch mount making it ready for refueling.
In theory this way it would be ready for the next launch in an incredibly short amount of time.
Now, this won’t work with a prototype, but later on,
if SpaceX actually manages to design a rocket booster that doesn’t need maintenance after each flight, which is the current goal,
it would speed up the launch cadence exactly to what Musk has been proposing for a long time.
Three launches per day and per booster.
Over and over again. At day and at night.
So fast, that right now this sounds like science fiction.
Working similar to a modern airliner.
Landing, being refueled and launching again right after the last flight.
That’s the goal and Mechazilla might just be the missing element.
If it works, that’s the reason for taking the risk.
Since there is no rocket in the world right now, capable of performing such a fast launch cadence of multiple launches per day,
SpaceX is forced to go new ways to achieve it.
If it was possible with current designs, other launch providers would already do it.
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The good stuff.
A huge thank you goes out to both,
Owe from SpaceX 3D Creation Eccentric and to Ryan from Ryan Hansen Space for providing us with all these animations to work with.
Links to their channels and Patreon accounts can be found in the description.
Show them some love! They certainly deserve it!
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