3D Printing

ISS and SpaceX Freezers Customized with Stratasys 3D Printing

Think you should be impressed that an ever-growing number of 3D printed parts have been cleared for flying? Then you should know that more and more parts have not only been cleared but have actually been regularly adopted on most current NASA and private space ventures.  They are not, however, rocket or engine parts, but custom “fridge” components and they have been developed by the University of Alabama Birmingham (UAB) Center for Biophysical Sciences & Engineering (CBSE) to facilitate the transportation and processing of experiments to and from the International Space Station (ISS), in accordance with NASA.

The UAB CBSE began as “a bio protein crystal growth engineering unit,” Daniel Sealy, Mechanical Engineer at CBSE said to Engineering Capacity. “We evolved into designing and building the storage and temperature control units for protein groves. Slowly, we developed into producing incubators and freezers capable of reaching -20ºC. The most current unit, Polar, is only -95°C, but our Glacier unit is capable of -160°C.” The project evolved as a byproduct of the labs’s research work on protein crystals and it might end up carrying it out in the end. Only in space.

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Polar is a powered, single middeck, -80°C freezer developed by the CBSE for the NASA Crew and Thermal Systems Division (CTSD).  It is also capable of operating within SpaceX’s Dragon Capsule, the Cygnus Pressurized Cargo Module, and the International Space Station (ISS) EXpedite the PRocessing of Experiments for the Space Station (EXPRESS) Rack. It is additionally capable of being transported via soft stowage aboard the HTV and ATV vehicles.

The main function of Polar is to provide a -80°C freezing and storage unit for a broad range of science samples during transportation to and from and while aboard the ISS. Its first flight took place just last January, on the SpaceX CRS-5 mission, and there are currently three active Polar freezers with a total of fourteen full active units set for a future date. Space on the space station is limited and carefully regulated to optimize the interior capacity and exterior dimensions, so a team of engineers and scientists from UAB CBSE turned to 3D printing.

After a couple of failed attempts at using thermoformed and machined PEEK, 3D printing was discussed as a potential solution. The team was already using Stratasys industrial-grade Fused Deposition Modeling (FDM) 3D printing technology for ducting. “We discussed whether 3D printing would be feasible for the inner shell,” Sealy explained. “At first, we continued the line of thinking similar to thermoforming, in which many pieces would be printed and joined together. But after some research, we realized there were printers with a large enough printing volume that the entire shell could be printed as a single piece. This led us to where we are now. We had to go through a lot of learning about how to design for 3D printing and what types of geometry worked well, but it seems to be working great.”

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Sealy and his team used the ultra-strong, flame and chemical resistant ULTEM 9085 material, a powerful polymer developed by Saudi Arabia’s SABIC group and used primarily in high-performance Stratasys Fortus 3D printers. It has a melting temperature of well above 300°C and using it in an extreme cold environment is uncommon.

“As this isn’t a structurally critical area, we did minimal testing,” says Sealy. “But it does have to withstand the rocket vibrations as it journeys to the station.” Sealy and his team performed 3-point bend tests on the ULTEM 9085 material, freezing it, and simulating the stress it’d be expected to experience. “We dropped it from certain heights, bent it – generally made sure it wouldn’t shatter, chip or break. Once the first unit was built, it also had to undergo vibration testing on a shake table that simulated what it would see during launches to verify that the entire design didn’t have any issues, and the Ultem performed well with no issues in that testing.”

The Polar freezer will house an amalgam of scientific samples, largely biological – such as blood, urine, and tissue cells – on the space station itself to study the effects of zero gravity on human cells over time, among other experiments. The next up will be the Glacier model, which will take the temperature down even further. It will require some further testing on the low temperature resistance of ULTEM, but 3D printing will certainly come in handy for that model as well.

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