If you want to take to the skies or fly to
Mars, you’re going to need a machine to 
get you there.
Humans dreamed of taking flight for thousands
of years, but it took special tools, techniques,
and materials to make it possible.
It took aerospace engineering.
[Theme Music]
We’ve been able to accomplish some
remarkable things since machines have given us
the power of flight.
Astronauts visited the Moon in less time than
it takes to cross the Atlantic by boat,
and my direct flight from LA to Missoula takes
less time than it takes to drive across LA County.
We’ve been able to do these things because
of aerospace engineering, the field dedicated
to designing and building machines that fly.
It’s broken down into two main parts: aeronautical
engineering and astronautical engineering.
Aeronautical engineering is focused on making
aircraft – like gliders, jets, and helicopters
– while astronautical engineering builds
spacecraft – like probes, satellites, and spaceships.
Both disciplines made enormous strides in
the 20th century thanks in part to the Cold War
conflict between the US and the Soviet Union.
That rivalry gave us the race to land on the
Moon, as well as advancements in jet propulsion,
radar, materials science, and so much more.
Today nations still compete, but so do private
companies – and the goal isn’t just getting back
to the Moon, but making it to Mars.
It’s not only a good headline.
If we’ve learned anything from the Space
Race, it’s that competition drives innovation.
The rocket company SpaceX plans on sending
people to Mars as early as 2024 and, to make
that happen, you need a lot of innovation.
But whether you’re sending people across space
or just flying around in the atmosphere, you’re going
to need to know some basic flying principles.
For atmospheric flight, the critical one is
lift, and the most basic form of lift is buoyancy.
Buoyancy works because the atmosphere has
what physicists call a pressure gradient,
meaning that air pressure gets a tiny bit
smaller for every little bit higher you go.
The difference in those pressures creates a
small upward force, which can push an object
up if it’s light enough – that’s lift!
The earliest form of flight, hot air balloons,
uses this principle.
That big ball of hot air is pushed up because
it’s lighter than the surrounding cooler air, and it
pulls its passenger along for the ride.
If you want your balloon to be stationary, what
engineers might call in equilibrium, then the sum
of the forces should be equal to zero.
That means that the weight of gravity pulling the balloon – and the gas inside – downwards needs to exactly balance out the force of the pressure gradient pushing up.
But balloons are pretty impractical for most
applications.
They’re so dependant on the surrounding environment
that things like changing weather conditions can make
it hard to precisely steer or even land in one.
To fly more effectively, you need a propulsion
system, or something that pushes you forward.
A propulsion system usually consists of a power
source, and a propulsor, which is something that can
convert power into forward motion.
There are three main propulsion systems that
you’ll use as an aeronautical engineer:
a heat engine with fuel, an electric motor
with batteries, or an electric motor with
solar cells.
The goal with any of these systems is to provide
enough thrust to overcome the drag of the aircraft.
For commercial airplanes that do a lot of
consistent travel,
you’ll want to keep the engine efficiency high
and fuel usage low so that you’re not burning a
hole in your wallet.
For something like a fighter jet, where speed is key, you’ll
need more thrust to accelerate quickly, which means
that engine efficiency might go out the window.
Most modern planes rely on the jet engine,
which has five core elements: an inlet, compressor,
burner, turbine, and nozzle.
The inlet brings air into the engine, and
that air is fed to the compressor.
The compressor then increases the pressure
of the incoming air before it enters the burner.
At this stage of the engine, that high-pressure
air is combined with fuel and burned.
This creates hot exhaust gas that’s used
to turn a turbine, which produces thrust as
that air is passed through the nozzle.
Finally, the nozzle acts as your propulser,
pushing the plane forward.
Now, there’s a few important things to consider
here.
You need to make sure that you have a sturdy
inlet that can operate efficiently –
meaning that it can bring in enough air to the
compressor – for your aircraft’s entire flight.
When you’re flying at low speeds, your compressor
can handle pulling air into the engine itself,
but at higher speeds, a good inlet design allows you
to have better maneuverability without disrupting the
air flow to the compressor.
You also need to design your engine with materials
that can withstand a lot of heat.
For instance, the blades in your turbine can
experience temperatures of several hundred
degrees Celsius.
You need to make them from special metals that
can withstand that heat, like a nickel-based superalloy,
or add a system to actively cool the blades.
If you decide to cool them, you’ll need a hollow design so that you can pump cool air into the blades and out through small holes on their surface to keep everything cool.
Put that all together, make sure you have a
good nozzle to act as a propulser, and you’d
have yourself a quality propulsion system.
Now, that will get you pretty far here on Earth, but
think about traveling to space and you’re going to
have to deal with a whole other slew of challenges.
And the biggest one is actually you.
You might think that technological limitations
are what’s stopping us from traveling the stars –
and that’s certainly part of it.
But your greatest obstacle will come from
the human body’s difficulty in adapting to the
challenges of deep space.
Our bodies can’t just flip a switch and
suddenly adapt, so you’ll need to build ships that
can mimic an Earth-like environment.
Some aspects, like creating a breathable atmosphere,
are pretty easy.
Others, like dealing with weightlessness are
much harder.
One thing we don’t yet have is artificial
gravity.
Gravity affects everything from the development
of your bones and muscles, to how easily your
heart pumps blood through your body.
Without it, astronauts in space experience
issues like weaker muscles or blurrier vision
after just a few days
One way to deal with this, at least in theory,
is to take advantage of the apparent centrifugal
force and create a spacecraft that spins.
This could effectively mimic gravity in a
similar way to how water stays in a rapidly
spinning bucket.
Space is also full of radiation, which can
increase the crew’s risk of cancer and even
hurt the ship.
Long-term exposure to radiation can severely
damage onboard electronics, causing short-circuits
and corrupting memory.
So if you don’t want your design to
get fried in space, you need to build it to
withstand that radiation.
Using insulating materials for computer chips
instead of the usual silicon will help.
So will designing electronics to have external
shields made out of things like lead.
That’ll make the overall size of your system
larger, so you have to factor that in too.
And that’s just space itself.
There’s even more to consider once you start
talking about dealing with the atmospheres
of other planets.
Take a look at Mars, and you’ll find an
atmosphere about 1% as dense as Earth’s,
and a temperature that ranges from -125°C in
the winter to about 20°C in the summer –
all things that your designs need to be
able to handle if we ever have hopes of
traveling or even living there.
But before you go off and try and colonize
another planet, it’s good to start of with a
simpler mission,
like designing a satellite that doesn’t have all the
problems of needing an astronaut on board.
Satellites have three main elements: the payload,
the bus, and the launcher.
The payload is all the equipment that performs
the satellite’s main functions, like receiving
telecommunications or processing and sending data.
The bus refers to the systems and structures
that provide functions like power, protection,
stability, and orbital control –
which all allow the payload to perform its
intended mission.
The launcher, or the launch vehicle adapter
assembly, is the connection between the bus and
the rocket that boosts the satellite into orbit.
All of these parts need to come together in
the design of your satellite.
And you better make sure all your math is right, because a simple calculation mistake can be devastating, both in terms of human life and in the cost of all your equipment.
Back around the turn of the millennium,
NASA lost a 125 million dollar Mars orbiter just
because of a mix-up of units.
NASA’s team was using metric units while
the manufacturer was using English ones,
ultimately throwing off the orbiter’s calculations
and causing it to burn up in the Martian atmosphere.
There’s one last, special kind of spacecraft
you might need to design, a spacesuit.
You see, a spacesuit isn’t just a set
of clothes that you wear in space – it’s
basically it’s own human-sized ship!
It protects an astronaut from getting too
hot or too cold, provides them with oxygen to
breathe, and can even store drinking water.
And they have those gold-lined visors that
shield their eyes from the super bright sunlight
of space.
And the suit’s tough exterior provides protection from
space dust, which can actually be really dangerous when
it’s moving around faster than a speeding bullet.
You can’t beef the suit up too much though,
because astronauts still need to be able to
move around effectively.
Conserving energy is also important since
the food options are a little more...limited
up there.
That’s why engineers are always trying to
come up with better spacesuit designs, like
NASA’s Z-2 advanced prototype.
The Z-2 uses advanced composites to achieve a lightweight, highly durable suit that could withstand long duration missions in harsh environments, like the one found on Mars.
Whether it’s SpaceX, NASA, or someone else,
whoever plans on getting to Mars will need
spacesuits like these.
And a good spaceship.
But with the right engineering practices,
and a little luck, there’s a good chance that we’ll
one day be a multiplanetary species.
Today we learned all about aerospace engineering
and its two main fields of aeronautical engineering
and astronautical engineering.
We applied the concepts of lift and buoyancy to
flying, and found out how a propulsion system is more
effective than something like a hot air balloon.
Then we learned how managing the human
body in space is one of the biggest challenges
that aerospace engineers face.
Finally, we learned what goes into making
a good spacesuit.
I’ll see you next time, when we talk all
about computer engineering.
Crash Course Engineering is produced in association
with PBS Digital Studios, which also produces Space Time!
Explore the outer reaches of space, the depths
of astrophysics, and anything else you can
think of beyond Planet Earth.
Check it out at the link in the description.
Crash Course is a Complexly production and this
episode was filmed in the Doctor Cheryl C. Kinney
Studio with the help of these wonderful people.
And our amazing graphics team is Thought Cafe.
