Tim Dodd the Everyday Astronaut here to talk a little bit more about how exactly SpaceX
lands the first stage of their massive Falcon 9 rockets.
Now previously we've showed you why they don’t use parachutes and also why they land on land
sometimes and on the drone ship other times.
Well today we’re going to show you how they use these things that look like giant waffle irons
alongside some nitrogen thrusters and the rocket’s engines themselves to actually steer to a bullseye
from over 70 miles in altitude and going up to 5,000 miles an hour!
We’re also going to show you what you’re seeing when SpaceX puts this up on their webcasts.
Let’s get started.
After doing the work of helping loft a payload into orbit, the remaining few minutes of most
rocket boosters life is spent coasting up to its highest point (or apogee) and then
falling back to Earth only to be destroyed when they either hit the ground like they
do for China or Russian launches or as it crashes into the ocean like those launched from the United States.
In order to successfully recover a booster, the booster must do a few things.
1. Land
2. Don’t blow up
With additional bonus points for landing on target
Well actually, that landing thing is really important.
The Falcon 9 often lands on a ship that’s roughly the size of a football field in the ocean.
If it misses, it’s doomed to be a future coral reef at the bottom of the ocean.
If it's landing on land it has the risk of coming down over populated areas.
So that being said, being able to control it on its way back down is probably just as
important as aiming the rocket on its way up.
Before we dive into this, let’s take a look and summarize what a Falcon 9 first stage
booster does after it separates from the second stage.
Lucky for us, SpaceX captured some incredible footage during mission, NROL-76 on May 1st, 2017.
First the first stage performs a flip maneuver to point itself backwards using cold nitrogen
gas thrusters.
Then the Falcon 9 lights up 3 of its 9 engines for the boostback burn (which it sometimes
omits depending on the mission).
Then it deploys its grid fins.
Once it starts to hit dense atmosphere, it lights up those same three engines again for
its entry burn.
As it falls through the atmosphere it steers itself using grid fins.
With less than 30 seconds remaining, the Falcon 9 lights up 1 to 3 of its engines just before
deploying the landing legs and coming to a nice smooth touch down.
They make it look so easy.
So let’s talk about each of those three mechanisms quick, First is the cold nitrogen
gas thrusters.
The Falcon 9 has two pods containing 4 nitrogen thrusters that sit way up on the top on the
interstage portion of the booster.
These little thrusters orient the vehicle in the vacuum of space.
They also perform the initial flip maneuver which points the rocket engines in the retrograde
to start slowing the vehicle down during its boost back burn.
You’ll see the little puffs of nitrogen as it continually hones in on its target.
Next is everyone’s favorite, grid fins!
Grid fins were developed in the 1950’s in the Soviet Union.
They’re a fin that’s gridded, or a gridded fin if you will that can fold flat against
the fuselage of the rocket or in most cases missile.
That’s right, these are most common on missiles since they can fold up and tuck away, allowing
for compact storage of the weapon in a silo or payload bay.
SpaceX certainly isn’t the first company to use grid fins on rockets.
Oh no no no no.That goes to the Soviet Union who put grid fins on both their Soyuz and
their moon rocket, the N1.
Grid fins are the perfect choice for the Falcon 9 since the fins can be deployed in flight.
This allows for them to be tucked away and streamlined on ascent and then deployed for
the descent portion.
Lastly you’ll notice the engines of the Falcon 9 gimbaling.
The engines can pivot several degrees, and rather quickly, which can provide a lot of
control over the stage.
Think of balancing a broomstick.
You can not only keep the broom vertical, but you can also apply force horizontally
and change your position with only input from the very bottom.
Ok let's take this over to Kerbal Space Program where I'm going to try to land the first stage of a Falcon 9!
Ok so our Falcon 9 is loaded up in Kerbal Space Program.
Without further adieu let's take off!
3. 2. 1.
Liftoff!
Oh yeah!
Look at those 9 merlin engines burning bright.
Beautiful.
Ok so here's our gravity turn.
That means we're going to be turning a little more sideways until we're eventually pitched
all the way over and making all of our velocity go in the horizontal vector and not just vertically.
Ok main engine cut off and here comes stage separation.
And there goes that second stage, it's going to continue going on into orbit while we do
our little flip maneuver here with this nitrogen thrusters.
And now we're going to light up 3 of those 9 merlin engines for that boost back burn.
This is going to make us go west instead of east.
Boost back burn looks good.
Engine cut off.
Alright let's pop out those grid fins.
This view may look familiar to you.
SpaceX uses a view very similar to this in their webcasts.
It's looking down from the interstage of the rocket all the way down the first stage and
you can kind of see the grid fins there.
It's a really cool view but it looks a little confusing in real life.
Ok so we were still going up and we're about to start falling down now.
There's apogee, our highest point.
Now we're falling back.
We're using those little nitrogen thrusters to orient ourselves perfectly as we get ready
for our entry burn.
Let me show you what this is, we're going to pull back a little bit and zoom around.
You can see how we get into this position and that's about where the camera is.
Alright here's our entry burn.
We're going to light up three of those nine merlin engines again.
Alright getting a little spice on this stage here.
This slows the rocket down so it doesn't get obliterated as it goes through the atmosphere.
Entry burn is complete.
Those grid fins start to have more and more control as we get into the thicker atmosphere
and they just keep aiming that first stage at its target.
Woah.
Settle down there jim john.
Alright and here's our landing burn it's just one engine.
Ok looking good looking good.
Oh this is it!
Landing legs out!
Oh this is looking good!
Alright here we go!
Ohhhhhh yes!
Touch down!
On our very first try!
No!
No! ughhhh
So hopefully this gives you a good idea of how SpaceX controls a 15 story rocket that
falls from the edge of space.
If you have any other questions about how SpaceX lands its rockets or any other question
about rockets in general, leave them in the comments below.
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Thank you!
Well that does it for me.
I’m Tim Dodd the Everyday Astronaut.
Bringing space down to earth for everyday people.