By Lauren Robinson
Young scientists are racing to deliver by October a satellite payload of instruments to test freeze-casting — technology that could free space explorers from expensive, time-consuming deliveries of supplies from Earth.
The team of Northwestern University undergraduates building the innards for a small satellite called a “CubeSat” missed the launch window last year but are getting ready for another try.
“The sample container failed,” explains Kristen Scotti, a graduate student and mentor for SpaceICE, the initiative creating the CubeSat instrumentation to test freeze-casting for eventual manufacturing needs in space. Essentially, the glass containers for three sample suspensions were cracking, and anything less than airtight would jeopardize the freeze-casting process, dependent upon controlled temperatures and accurate readings.
Freeze-casting can be used for manufacturing construction materials, battery electrodes and even food such as fake meat. Manufacturing what astronauts need to survive on other planets could reduce and eventually eliminate the need for massive deliveries to Mars or space stations.
Freeze-casting starts with a simple liquid suspension of tiny particles. The suspension gets frozen, then sublimated — evaporated such that it changes directly from a solid to a gas — and the particles left behind form a microscopically porous mold. Because these molds are porous, they have less mass.
Scotti and others are curious about how freeze-casting works in microgravity: that is, how the particles disperse and the fluids freeze in space where gravity is nearly absent, but not quite. By better understanding gravity’s role in the process, the scientists hope to improve it here on Earth. So, they began SpaceICE in 2016 and have since seen a rotating team of undergraduates devote their time to building out the payload.
Researchers and students at University of Illinois Urbana-Champaign are building the CubeSat, which measures about 10 cm x 10 cm x 30 cm. Ultimately, NASA will launch it to the International Space Station, where it will be tossed out to go into orbit. Researchers will receive data from the experiment digitally over a six-month period.
For the samples, the Northwestern students will use an aqueous particle suspension — “a fancy way of just saying we have a bunch of little particles suspended in the water,” said project team leader Robert Lundberg. In this case, we’re talking about micron-scale silver-coated glass beads.
After the canisters that would contain the suspensions showed signs of cracking last spring, students including Lundberg and lead engineer Dominic Herincx were forced to rethink their design.
“It wasn’t feasible or responsible to just rush it to make that same launch date,” said Herincx, who has been working on the project since fall 2017.
That was hard for the students, including sophomore Chelsea Ye, who joined on last spring.
“It seemed like we were set to deliver the entire thing. So I was just going to be there to work on the last bit of it, to work on manufacturing and stuff,” Ye said.
But then the team realized the initial design for the sample containers was not going to work. “That was, like, really stressful,” Ye said.
Sending equipment into space is a high-stakes undertaking. Not only is it tricky to get every variable just right, it’s also expensive. So the folks at NASA worked hard to keep the project on track for the initial launch date when the sample containers showed signs of failure.
Brenda Dingwall, the SpaceICE mission manager at NASA, was the point person for this stage. She appealed to NASA administrators for continued support, and she connected the students with mechanical engineers who might be able to help with the containers. But the redesign — and missed deadline — eventually became inevitable.
“It’s always hard when you have to push back a launch date,” Dingwall said. “I’ve been in the space business a long time, and nobody ever wants to see that happen. But it’s a reality of the business we’re in.”
Herincx and Lundberg graduate this month. The students’ goal is to wrap up the payload by graduation, well before they have to deliver it to UIUC, where students will fine-tune “the bus” — that is, the CubeSat — before NASA launches it in April 2020.
The crew has a lot of variables to consider when redesigning the sample containers, each of which is just a few inches tall and about an inch wide. The satellite payload will contain three sample containers, from which researchers will collect temperature data and imagery pertaining to every point in the freeze-casting process.
One important consideration is that the glass the container is made of has to be sturdy enough to withstand vibrations during launch, plus expansion and contraction under changing temperatures and pressure. But the glass also can’t be too thick, because that could render the temperature gauge — thermistors touching the outside of the glass — inaccurate.
At a recent team meeting for the project, Lundberg, Scotti, Herincx and project leader David Dunand, a materials science professor, sat around a small table in Dunand’s office and deliberated the tweaks they could make to the glass to make it chip-proof. If the glass develops a chip, it’s prone to cracking, Dunand said — “game over” for the experiments.
The team initially planned to use Pyrex glass blown around conductive Kovar plates on either end. But the glass was weakened where it came into contact around the Kovar. And, the diameter of the vessel was inconsistent because of this design, posing a problem because the O-ring seal, a rubber seal on the inside of the vessel meant to keep out air, didn’t fit snugly throughout the container.
For the redesign, the team is using Pyrex glass that fits snugly inside a Teflon shell. The Teflon evades the troubles with the blown glass, but it isn’t conductive. The team needs a base that can transfer heat in order to induce the temperature gradient that freezes the ice upward.
Scotti is in the midst of testing copper strips that will perform that task, but running the copper strips out from under the sample containers could be tricky given the limited space inside the satellite. There still has to be room for the circuit board in the center of the payload.
The challenges haven’t been enough to deter the undergraduates, who persisted with the CubeSat project even as they contended with final exams and post-graduation plans.
Scotti, who herself began the project as an undergraduate, said she had feared the students would give up after missing the deadline last year. “And they haven’t. They’re just continuing on, going going going, which is great.”
Ye explained that the failure served as a kind of life lesson.
“I think it’s really important to learn that not everything is going to be perfect the first time,” she said.