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This episode is brought to you by the Music for Scientists album! Stream the album on major music services here: https://biglink.to/music-for-scientists. Check out the “For Your Love" music video here: https://youtu.be/YGjjvd34Cvc.

Scientists are always searching for new materials that maximize strength and thermal protection while also minimizing mass for space flight. So, when developing new heat shields, why are they looking to cuttlefish for inspiration?

Hosted by: Caitlin Hofmeister

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Sources:
https://www.washingtonpost.com/wp-srv/articles/A38144-2003Feb6.html
https://www.encyclopedia.com/science/news-wires-white-papers-and-books/heat-shields
https://interestingengineering.com/what-keeps-spaceships-from-burning-up-during-reentry
https://www.faa.gov/about/office_org/headquarters_offices/avs/offices/aam/cami/library/online_libraries/aerospace_medicine/tutorial/media/iii.4.1.7_returning_from_space.pdf
https://www.sciencedaily.com/releases/2020/09/200911141711.htm
https://www.nature.com/articles/1841330a0
https://www.pnas.org/content/117/38/23450
https://www.thechemicalengineer.com/news/3d-printed-ceramic-foam-is-stronger-lighter
https://www.researchgate.net/publication/316178034_Extreme_lightweight_structures_Avian_feathers_and_bones
https://ocw.mit.edu/courses/materials-science-and-engineering/3-054-cellular-solids-structure-properties-and-applications-spring-2015/lecture-notes/MIT3_054S15_L18_Nat_trans.pdf
https://www.technologyreview.com/2019/06/26/134445/nasa-engineers-build-better-heat-shield/

Image Sources:
https://commons.wikimedia.org/wiki/File:Columbia_Memorial.JPG
https://aip.scitation.org/doi/10.1063/1.4993202
https://commons.wikimedia.org/wiki/File:Bones_(human,_bird).png
https://commons.wikimedia.org/wiki/File:3D_visualisation_of_%C2%B5CT-data_of_a_cuttlebone_05.jpg
https://commons.wikimedia.org/wiki/File:3D_visualisation_of_%C2%B5CT-data_of_a_cuttlebone_01.jpg
https://spaceflight.nasa.gov/gallery/images/apollo/apollo8/html/s68-55292.html
https://commons.wikimedia.org/wiki/File:Apollo_12_heat_shield.JPG
https://mars.nasa.gov/mer/gallery/artwork/entry_br.html
This episode is brought to you by the Music  for Scientists album, now available on all   streaming services. {♫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♫}.