This episode is brought to you by the Music for Scientists album, now available on all
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{♫Intro♫}
For a spacecraft returning to Earth, hitting the atmosphere is kind of a traumatic experience.
Friction between the air and the ship creates an
incredible amount of heat—we’re talking thousands of degrees.
Because of that, engineers protect the front of the spacecraft with
a heat shield to keep the rest of the vehicle from burning up.
Except, designing heat shields that can withstand that heat
and not weigh down the whole ship is no small job.
So, scientists are always on the lookout for new materials that maximize strength
and thermal protection while also minimizing mass.
And inspiration for that next-gen material might be coming from a surprising place:
a small marine creature known as the cuttlefish.
Over the years, heat shields have been designed a number of ways,
with each generation trying to overcome the problems of the last.
Like, early capsules used ablative heat shields that were designed to vaporize in the atmosphere,
carrying heat away from the crew inside.
The problem was, they were expensive and heavy -- they could add over a thousand kilograms to a
capsule. Plus, they were only good for one use, since they literally burned up during reentry.
So, NASA’s space shuttles used ceramic tiles, because they could withstand the heat while
being reusable and lightweight. However, they weren’t without their own issues.
Thousands of individual tiles had to be glued to the spacecraft’s exterior,
and each could come off separately.
They were also easily damaged.
Like, famously in 2003, damage to several tiles by a falling piece of foam caused the
tragic destruction of the Space Shuttle Columbia and the loss of its crew.
So, as we keep sending people to space, engineers are always looking for better,
safer heat shield materials.
And that’s where cuttlefish might come in.
Cuttlefish are cephalopods, so like their cousins octopuses and squid,
they have a soft body and no bones.
That said, they do have a shell-like structure on the inside of their bodies, known as a cuttlebone.
Cuttlebones are made of a crystallized form of calcium carbonate known as aragonite.
And this material is arranged in such a way that there are pockets
inside the cuttlebone that trap gas — mostly nitrogen.
Cuttlefish can also pump water into these cuttlebones, and that’s how they control
their buoyancy. By adjusting the balance of water and gas in these structures,
they can become lighter or heavier, and sink or rise through the water.
In general, researchers have been investigating the internal
microstructure of the cuttlebone to determine what makes it both strong and porous.
And along the way, they discovered some features that may help spacecraft engineers.
In a 2020 study, researchers mapped the cuttlebone’s microstructure and
revealed a unique design made of individual, separated chambers with floors and ceilings.
These chambers are supported by vertical walls, similar to the structure of bird bones.
But unlike birds, the cuttlebone’s chambers are supported by wavy walls instead of straight ones.
The waviness increases up each wall, getting more wavy from floor to ceiling.
So, when the cuttlebone gets compressed, say due to a predator’s bite, the wavy
design means cracks form in the middle of the walls, rather than near the tops or bottoms.
This ultimately allows the walls to dissipate energy better instead of quickly collapsing,
so the structure can absorb a lot of energy while minimizing damage.
And this waviness isn’t random: Cuttlefish hit a sweet spot when evolving this wavy gradient.
In their paper, the researchers manipulated a computer model of the structure and found that,
when they increased the waviness, the cuttlebone became less stiff.
And decreasing the waviness made the cuttlebone more brittle.
So, this unique design makes the cuttlebone a perfect combination of lightweight,
stiff, and shatter-resistant when damaged.
Which all sounds like good elements of a heat shield!
Specifically, taking inspiration from these animals might help us
make heat shields out of a new material: ceramic foams.
Ceramic foams are porous, and look a lot like the regular foam you might buy to pad a cushion,
but instead of being squishy, they’re made of stiff, hard material.
These foams can withstand high heat and are chemically stable,
but they’re rarely used because of their brittleness.
So, if we could give them the structure of a cuttlebone, that could solve our problem!
And this could be done by 3D printing a heat shield with the same wavy, structural design,
using ceramic foam inks.
So, as humans venture beyond the International Space Station,
an improved heat shield could help us reach new places.
For instance, while traditional heat shields have been used to put landers and rovers on Mars,
the thin Martian atmosphere would require a shield as big as 20 meters across to safely carry people.
Something that large would need to be as light as possible,
which might make a cuttlebone-inspired material the ideal choice.
So, go figure. Exploring the deepest depths
of space might require a little help from the depths of the ocean!
If you liked this episode of SciShow Space, you might also enjoy the Music for Scientists album.
It’s a tribute to folks who’ve dedicated their lives to science-driven work,
pushing the boundaries of our understanding and our view of the world.
The songs were written and recorded by Patrick Olsen. And since you’re watching SciShow Space,
I recommend you start with the song “Moons of Jupiter,”
which was inspired by seeing Jupiter’s moons in some binoculars.
If you want to check it out, click the link in the description to start streaming.
{♫Outro♫}