Even though astronomy is my first love, sometimes I wander away and explore other science. This week, I attended a mechanical engineering conference and sat in on sessions specifically devoted to the influence of origami in engineering design. Lucky for me, there have been a few talks that combine this area of engineering with space-based applications.
One of the coolest was a compressible tube whose structure is based on origami folds. This type of tube (called a bellows) has all kinds of uses on Earth — like connecting a jet bridge to an airplane’s open door — and in space, it can protect a smaller tool that lies inside the bellows but can extend out.
The most advanced rover currently rolling around Mars, Curiosity, has a drill as part of its system that samples material on the planet. That drill and its associated instrumentation lie within a metal bellows. NASA next Red Planet rover, Mars2020, will also be equipped with a bellows. And researchers have been working on an origami version for future space exploration missions.
A bellows needs to be able to compress — for storage — and expand as needed. (Think again of the bellows that lies between a jet bridge and an airplane. Both the bellows and jet bridge are compressed and closest to the terminal when not in use.) The metal bellows that will fly on Mars2020 has a 1:8 compression ratio, meaning its expanded length is 8 times its compressed length. But what if you could make that ratio a smaller number?
Origami is the art of paper folding, so, perhaps unsurprisingly, its influence leads to a bellows with a much smaller compression ratio: 1:30. And that leads to a smaller compressed structure. Brigham Young University’s Jared Butler, one of the researchers working on this origami bellows, explains why this is beneficial. “If I can reduce the amount of volume my bellows takes in compressed state, I can also reduce the amount of shaft length that is used to stow that bellows, which reduces the mass of my mechanism.” And that’s good news in spaceflight.
The researchers had focused on a bellows that could fly on Mars2020, and that meant they could compare its lab-tested specifications to the metal bellows on Curiosity. After deciding on the fold pattern, called Kresling, they folded by hand several samples of different flexible industrial materials and films (like polyethylene). The Red Planet is home to harsh environmental conditions, so to ensure their origami bellows could withstand those conditions, Butler and his colleagues worked with the Jet Propulsion Laboratory.
To simulate martian dust storms, they placed the bellows in a contraption where a powerful fan whipped around sand particles, battering each bellows. Mars’ thin atmosphere blocks very limit ultraviolet (UV) radiation at the surface, and to test that exposure, the researchers placed each sample in another chamber with a deuterium light bulb to bathe each bellows with a high UV dose. To test for the wide temperature swings between each day and night, Butler and his colleagues used a different chamber with dry ice and watched how many compression-expansion cycles the samples could withstand. The key was testing how soon the structure tore (if it did at all), which not surprisingly occurred on the point, called the vertex, where multiple folds met. While they had very promising results, NASA chose the previous metal bellows design for the future Mars2020 rover.
A bellows for an ARM
But that doesn’t mean the work was for naught. A mission still in the development stages would use a larger version of this Kresling origami bellows — if the mission gets the go-ahead from Congress. This is NASA’s Asteroid Redirect Mission (ARM), and it’s a bit controversial (but that’s another story for another day). In this project, a larger drill would stay contained within the origami bellows the entire time, expanding and compressing when in use. With ARM, the instrument would operate not on a planetary surface but on a small asteroid flying through space. This type of environment’s harsh conditions are different from those on the martian surface. For example, there aren’t dust storms to contend with in open space, but there are micrometeoroids. The good news is the drill and bellows would sit within a titanium cage, which would block the meteoroids and any UV radiation. They still need to test for rocky debris: that’s material that the action of drilling into the asteroid would fling up, says Butler. A bellows would protect the rest of the spacecraft, its mechanics, and gears from that debris.
So far, this origami structure has passed every test the researchers have put it through. The BYU team still has a few unresolved issues, though, with the bellows. First is that all the samples they’ve worked on have been hand-folded. With 59 fabrication folds per sample, there’s bound to be inconsistencies among the samples. They need to come up with another way to make the exact same structure every single time.
Another issue is that to end up with a cylinder, you have to take a flat sheet, crease the folds, and then connect two opposite edges of that sheet to form a cylinder. Tape and other similar adhesives don’t work at the frigid temperatures of space. The engineers have sewn along that edge with Kevlar thread, but that puts small holes into the bellows as a result of the stitching. But Butler isn’t worried about overcoming those obstacles.
Not just drills
The origami bellows isn’t the only space-based application of origami engineering. The large solar panels on spacecraft in addition to solar sails, which help space probes travel through space via the pressure from sunlight, have to be much smaller for launch. (The storage compartment in a rocket is only so big.)
And exoplanet hunters are also hoping that the near future will see another structure that could make use of origami’s influence. This would be a huge sunflower-shaped starshade that would fly in formation with a telescope and block the light from a star, allowing that telescope to look at the much fainter light reflected off an exoplanet. This shade would be 100 feet in diameter. And to safely cram that material into a rocket, one idea is to fold the central disk and then wrap the petals around the folded disk. Once in space, it would unfurl and unfold. Even though a launch-ready starshade is still a decade away, researchers are building prototypes in the lab to find the ideal fold patterns and material.
These space-based structures are only a few ways that engineers are incorporating the centuries-old art of origami. Of course, this influence is adding a coolness factor. But it’s also improving upon the technologies that have already flown in space.