WSU researchers are being funded by NASA and Blue Origin to research origami bladder designs for propulsion of fluids at very low temperatures.

Kjell Westra, doctorate student of philosophy and mechanical engineering at WSU, conceptualized the bladder for NASA Space Technologies Graduate Research Opportunities, which solicits an annual national competition for graduate students.

It takes a lot of energy for a rocket to reach space. One of the most energy-efficient propellants is hydrogen and oxygen, which must be cooled to cryogenic temperatures to exist as a liquid for storage, Westra said.

A bladder, which compresses similarly to a bellows, can be used to transport cryogenic propellants from storage tanks to engines without allowing any air bubbles. In zero gravity, air bubbles can form in the storage tanks, and if pumped into an engine it could cause it to explode, he said.

An example of where a bladder would be used is in reaction control system tanks, which fuel the many small rockets that reposition a bigger rocket in space, Westra said.

The more “high in the sky” application of bladders is in interspace fuel depots, but the size and scope of those bladders are not achievable right now, he said.

“In space right now, when you launch a rocket, you have to carry all of your fuel with you,” he said. “It’s like if you wanted to go on a road trip to Maine, but you couldn’t stop at any gas stations along the way.”

The origami design of the bladder they work on is meant to solve the issue of embrittlement, which is when material like plastics or metals becomes brittle at cryogenic temperatures, he said.

“You’ve heard of the cliché, right? … Someone pours liquid nitrogen on a lock, hits it with a hammer and shatters it,” he said.

His origami design, which is based on the Kresling design, uses a series of panels and folds to globalize movement, which minimizes local movement. This keeps the bladder from shattering when the material is brittle, he said.

“The idea here is that we can, using origami, still be able to efficiently expel all the propellant inside of the tank while limiting stretching anywhere,” he said.

Meanwhile, Francis Dunne, doctoral student in material science, seeks to come up with new and more efficient materials to make origami bladders from, which is being funded by Blue Origin.

“What matters most is the maximum allowable bend radius of the material you’re dealing with … how much can the material bend before it cracks,” Dunne said.

Dunne believes he can optimize the bend radius of a material by adding carbon nanotubes to polymer films, filaments made of plastic.

Carbon nanotubes are made by starting with a sheet of carbons one atom thick and rolling them into tubes. They are less than five nanometers in diameter, he said.

“The way I plan to do it is in a tube furnace. You react a few chemicals together at high temperatures and they kind of just grow on their own,” he said. “It’s about high purity chemicals and controlling, like, flow rates well.”

Current prototypes of the bladder are commonly manufactured with polycarbonate or Mylar®, he said. Polycarbonate is a cheap, mass-produced plastic, which is used in clamshell packaging and water bottles.

Mylar® is a common engineering plastic made by stretching crystalline polymers, repeated chains of molecules. In crystalline polymers, the chains are lined up parallel with each other and have a strong connection, he said.

“That’s why it has such good mechanical properties. It has very high tensile strength. It has a relatively high Young’s modulus for a plastic,” he said.

Young’s modulus describes the ratio of stress over strain. Silly putty has a low Young’s modulus because it stretches easily, while a ceramic plate, which stretches very little before breaking, has a high Young’s modulus.

Westra expects to be finished with the project by spring 2024 when the bladder will ideally have satisfied all of NASA’s requirements, he said.