Season 7
EP10 - The Space Shuttle (A meteor that survives the atmosphere)
Understand the insane engineering of the Space Shuttle re-entry and unpowered landing. Learn how thermal protection tiles survive 1600 degrees Celsius, why the orbiter is a hypersonic glider, and what made each landing a controlled miracle.
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"Flight control, this is Commander Shez. I have the runway in sight. Deploying landing gear."
And... touchdown! Flawless!
See? Everyone makes such a big deal out of the Space Shuttle returning to Earth.
It's just a fancy airplane! You drop out of space, point the nose at Florida, and glide down like a giant paper glider. Easy!
"A fancy airplane."
You think re-entry is an aerodynamic event. You think it's about flying.
An airplane flies through the air at 600 miles per hour using lift.
The Space Shuttle hits the top of the atmosphere at Mach 25. Seventeen thousand, five hundred miles per hour.
It has no engines. It has no fuel. It has the aerodynamic glide ratio of a vending machine.
You aren't flying, Shez. You are executing a controlled crash against the atmosphere itself.
To the Orbital Void. Let’s look at your "paper glider."
To stay in orbit, you do not just go "high up." You must go sideways so incredibly fast that as gravity pulls you down, you constantly miss the Earth.
That speed is Orbital Velocity.
The Shuttle weighs 100 tons. It is moving at Mach 25.
To land on that runway in Florida, you must bleed off an apocalyptic amount of kinetic energy. How do you stop?
Just use the brakes! Turn the ship around and fire the rockets in reverse!
Thrust against the momentum!
You can't. You are a victim of the Tyranny of the Rocket Equation.
To carry enough fuel into orbit just to stop yourself would require a rocket the size of a skyscraper. The Shuttle is practically empty by the time it reaches orbit.
You have no fuel. You have no brakes.
The only brake available to you is the air itself. You have to use the atmosphere to bleed your kinetic energy.
Okay, I get it! Air friction!
We rub against the air, the friction slows us down, and we glide home! Just like rubbing your hands together to get warm!
It is NOT friction!
That is the second greatest lie taught in elementary school science classes!
Feel the bottom of that pump.
(Touches it) Ow! It’s hot!
Did the air inside rub against the walls to get hot? No. You violently compressed the gas into a smaller volume.
The heating of re-entry is caused by Compressive Heating.
The Shuttle is moving at Mach 25. The air molecules physically cannot move out of the way fast enough.
The vehicle acts as a massive piston, crushing the air in front of it with millions of pounds of pressure.
The air compresses so violently that the gas molecules break apart.
It ceases to be a gas. It becomes a Plasma.
A 3,000-degree Fahrenheit shockwave of pure, ionized fire.
Three thousand degrees?!
But... if we want to be aerodynamic, shouldn't we point the nose straight forward? Like a needle? To cut through the air and avoid the heat?
If you fly like a needle, the shockwave physically attaches to the skin of the aircraft.
The heat transfer is absolute. You melt instantly.
This is why the Shuttle does not fly like an airplane.
It belly-flops.
Enter Blunt Body Theory, discovered by H. Julian Allen in 1951.
By presenting a massive, flat, un-aerodynamic surface to the airstream, the Shuttle creates a colossal pressure wave.
The blunt shape forces the superheated plasma to detach from the skin of the spacecraft.
90% of the heat is carried away by the airflow itself. You use the air as a shield against the air.
So... being as un-aerodynamic as possible... saves your life.
It really is just a flying brick.
Yes. But there is a catch.
Even with the shockwave detached, the radiant heat hitting the belly of the Shuttle is still over 2,500 degrees Fahrenheit.
What is an airplane made of, Shez?
Aluminum? Titanium?
Aluminum melts at 1,220 degrees Fahrenheit.
The structural skeleton of the Space Shuttle is aluminum. It is flying through an oven that is twice its melting point.
IT’S GOING TO MELT! We're flying a soda can through a blast furnace!
How does the crew survive?! Do they use massive air conditioners?!
You cannot out-cool 2,500 degrees. You have to block it.
You need a material that can sit in the fires of hell, completely absorb the heat, and absolutely refuse to pass it onto the aluminum hull just an inch below.
Enter the HRSI (High-Temperature Reusable Surface Insulation) tile.
The ultimate magic trick of material science.
Put your bare hand flat against the back of this tile.
(Hesitant, sweating) Are you sure?
Now. Watch.
(Blinking in surprise) I... I don't feel anything.
The front is literally glowing like the sun, and the back is room temperature! How?!
Pick it up by the glowing edges.
Are you insane?! I’ll lose my fingers!
Do it.
It’s glowing... but it’s not burning me. And it’s incredibly light! It feels like styrofoam!
Because it is 90% nothing.
It is made of extremely pure silica glass fibers, spun together so loosely that the tile is 90% empty air.
And air is an incredible insulator.
Thermal Conductivity. The ability of a material to transfer heat from one molecule to the next.
Because the glass fibers are so thin and mostly air, the heat literally has no physical path to travel through the block. The front of the tile can be 2,500 degrees, while the back is cool enough to touch.
The Shuttle’s belly was covered in 24,000 of these individually machined, unique tiles. They were glued directly to the aluminum hull.
Without them, the Shuttle would vaporize in exactly twenty seconds.
But because they are 90% air... they are incredibly fragile. You could crush this tile with your bare hands. A dropped tool in the hangar could crack it.
A piece of stray foam striking the wing during liftoff could shatter it.
Oh... Columbia.
Yes.
If even one crucial tile is compromised, the plasma shockwave finds the aluminum.
The thermodynamics of orbital velocity do not forgive gaps in the armor.
You thought it was a fancy airplane, Shez.
An airplane relies on aerodynamics. The Shuttle relied on a fragile, flawless mosaic of spun glass to survive the wrath of Isaac Newton.
It’s not flying.
It’s just falling... and hoping the glass doesn't break.
Every time that machine came home, it successfully dissipated the energy equivalent of a small nuclear weapon, entirely through the geometry of its belly and the chemistry of its tiles.
Never call it an airplane again.