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For the past decade, the entire world has
had their eyes on SpaceX as they have revolutionized
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rocket engineering and space travel.
From launching a sports car into orbit, to
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the promise of establishing a futuristic colony
on mars, their spectacles have generated levels
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of public excitement and media coverage that
haven’t been seen since NASA’s Apollo
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program which ended more than 40 years ago.
At the core of their ambitious plans is one
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of the greatest technological developments
in the history of rocket engineering: reusable
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rockets.
First announced to the public in 2011, the
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SpaceX reusable launch system development
program set out to create a new generation
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of launch vehicles that would drastically
reduce the cost of reaching orbit.
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To accomplish this, SpaceX proposed the seemingly
impossible task of recovering rocket boosters
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using powered-descent.
Their goal was to develop a rocket that could
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be launched vertically to deliver a payload
into orbit, and then return back to earth
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with a controlled descent and vertical landing
at a pre-determined landing site.
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Either on land, or on an autonomous floating
drone ship.
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In just 7 years, SpaceX was not only able
to achieve their goal of creating such a rocket,
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but they have proven that their system is
both reliable and economical with more than
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60 successful launches and 30 successful landings
of their Falcon 9 boosters, along with a 100%
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success rate since the completion of their
experimental testing program.
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Or at least that was the case until December
2018, but at least they had a pretty good
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run.
17 of their boosters were also re-used on
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successive missions, and their unit cost for
launching a kg of payload into orbit has been
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reduced to just a fraction of the nearest
competitor.
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But how exactly did SpaceX accomplish this,
and how do they manage to land 70 m tall rockets
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weighing in excess of ½ a million kilograms
precisely on a 50 m wide landing pad after
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they are launched more than 70 km into the
atmosphere at speeds exceeding 8,000 km/h?
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It all comes down to just 2 key things: experience,
and ridiculously well-engineered rockets.
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Let’s start with experience by taking a
brief look at the history of the reusable
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launch system development program.
The program itself was first announced in
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2011, but it wasn’t until late 2015 that
SpaceX was able to land a Falcon 9 booster
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on land successfully, and it took several
years beyond this to achieve a respectable
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landing success rate.
Before this, SpaceX spent 5 years conducting
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experimental landings where they tested their
new technologies and learned how to build
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better rockets through trial and error.
They began with a prototype vertical takeoff
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and vertical landing vehicle called Grasshopper,
which completed 8 successful flights from
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2012 to 2013.
Following the initial success of Grasshopper,
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SpaceX then equipped their first Falcon 9
boosters for powered-descent and conducted
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several soft landings on the ocean surface
from 2013 to early 2015.
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Unfortunately, these first tests with the
Falcon 9 were only able to achieve a landing
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accuracy of about 10 km, but this was greatly
improved in future tests.
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When the first landings on an autonomous floating
drone ship were attempted later in 2015, SpaceX
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endured a series of public failures as 4 consecutive
barge landings failed quite dramatically.
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Despite these failures, they obtained valuable
data from every single flight, and they used
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the failures as opportunities to learn from
their mistakes in order to develop a more
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robust landing system.
SpaceX continued to perform Falcon 9 landing
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tests through 2015 and 2016, both on drone
ships and on land, and successful landings
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became routine by early 2017, with SpaceX
deciding to stop referring to their landing
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attempts as experimental.
From the beginning of 2017 to nearly the end
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of 2018, SpaceX maintained a 100% landing
success rate with a minimum landing accuracy
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of just 10 m.
This impressive accuracy represents a 1000-fold
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improvement compared to the initial soft-landing
tests which were only able to land within
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a 10 km radius from the intended target.
But how did SpaceX manage to increase the
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landing accuracy of their rocket boosters
by 10,000% in just 4 years?
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Obviously, this wasn’t achieved through
experience alone, and so this brings us to
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point number 2: ridiculously well-engineered
rockets.
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When SpaceX performs a rocket launch with
the Falcon 9, the rocket separates into two
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stages in Earth’s upper atmosphere.
The second stage of the rocket carries the
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payload into space, while the first stage
booster returns to Earth and lands at a landing
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site for re-use.
The booster is programmed to follow a precise
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flight path back to Earth, and it must autonomously
perform a series of controlled maneuvers in
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order to maintain that path and land vertically
on the landing pad.
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The exact flight path depends on whether the
rocket is landing on a floating drone ship
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in the ocean, or on land, and for landings
at sea there is the added complexity of ensuring
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that the drone ship is in the correct position
when the rocket touches down.
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However, the greatest engineering challenge
by far is building a rocket capable of performing
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the maneuvers that are necessary for controlled
descent and landing.
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After stage separation occurs, the rocket
booster re-orients itself and performs a boost
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back burn to achieve the proper trajectory
towards Earth.
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During the descent, it performs a re-entry
burn which is used to reduce its velocity.
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As the booster approaches the landing site,
it re-orients itself again so that it is in
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line with the landing pad, it deploys its
landing legs, and it performs a landing burn
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to bring its velocity to zero as it touches
down on the pad.
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During the entire flight, from stage separation
to landing, the rocket continuously measures
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its orientation and velocity, and it adjusts
its trajectory accordingly so that it maintains
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the correct flight path.
To accomplish all of this, SpaceX has implemented
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several rocket technologies that were developed
and refined through their experimental testing
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program, and it’s these technologies that
have been pivotal to the development of their
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reusable high-accuracy rockets.
The six key technologies incorporated into
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the Falcon 9 rocket booster are as follows:
1) Thrust vector control.
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The merlin rocket engines of the first stage
booster are gimbaled using hydraulic actuators
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so that the direction of thrust can be adjusted.
This is a method of thrust vectoring that
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can be used to control the orientation of
the rocket both within Earth’s atmosphere
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and outside of Earth’s atmosphere where
aerodynamic control surfaces such as fins
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are ineffective.
Thrust vectoring is actually a common technology
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that is used for rockets, as well as military
aircraft and missiles, however it is absolutely
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necessary for the maneuverability of the Falcon
9.
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2) Cold gas thrusters.
The Falcon 9 is equipped with a total of 8
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nitrogen cold gas thrusters that are mounted
towards the top of the first stage.
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There is 1 pod on each side of the rocket,
each containing 4 thrusters.
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Like the gimbaled main engines, the cold gas
thrusters are used to control the orientation
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of the rocket.
They are particularly useful for the flip
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maneuver after stage separation because of
the large lever arm between the thrusters
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and the rocket’s center of mass.
They are also used to control the rocket at
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times during flight when the gimbaled main
engines are shut off.
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3) Re-ignitable engines.
Since the first stage must perform three separate
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burns after stage separation, it is necessary
for the main rocket engines to be re-ignitable.
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The engines of the first stage booster have
therefore been designed so that they can re-ignite
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in the upper atmosphere at supersonic speeds
as well as in the lower atmosphere at transonic
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speeds.
4) Inertial navigation and global positioning
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systems.
The Falcon 9 is equipped with an inertial
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navigation system, or INS, that uses several
types of sensors to measure the position,
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orientation, and velocity of the vehicle.
A global positioning system, or GPS, is also
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used to measure geolocation.
The onboard computer receives data from the
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INS and GPS in real-time and checks this information
against the pre-programmed flight path.
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If the computer detects any deviations from
the flight path, then it instructs the rocket
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to adjust its orientation and velocity as
necessary.
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5) Deployable landing gear.
In order to perform vertical landings, the
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Falcon 9 is equipped with 4 lightweight landing
legs that are deployed using high-pressure
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helium just before touchdown.
Each leg is constructed from carbon fiber
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and aluminum, and contains an impact attenuator
for particularly hard landings.
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The total span of the deployed landing gear
is approximately 18 m, and the entire landing
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system weighs less than 2,100 kgs.
6) Deployable grid fins.
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Four titanium grid fins are mounted at the
top of the first stage booster, and are deployed
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during the rocket’s descent back into Earth’s
lower atmosphere.
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The fins are aerodynamic control surfaces
that are used for precise control of the rocket’s
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position and orientation prior to landing.
The four grid fines alone are primarily responsible
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for the incredible 10 m landing accuracy of
the Falcon 9 first stage booster.
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Grid fins were first used on the fifth soft-landing
attempt of the reusable launch system development
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program in 2015, and iterations on their design
were continued through 2017 in order to achieve
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the accuracy that we see from SpaceX today.
So in the end, SpaceX was able to employ experience
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and good engineering to develop a reusable
and highly accurate launch vehicle, the Falcon
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9.
The Falcon 9 is an astonishing feat of modern
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engineering, and I hope that it sets a precedent
for the future of space travel.
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Without a doubt, the development of a reusable
launch system has been one of the greatest
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technological developments in the history
of rocket engineering, and I can’t wait
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to see what the future has in store for SpaceX.
Or perhaps I should rather say, what SpaceX
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has in store for the future.
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I really hope that you enjoyed this video, and I hope that I was able to provide some insight into the landing
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technology used by SpaceX.
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