“We put a prototype in a vacuum chamber, shined light on it, and saw it flip over,” remembers Ben Schafer (Harvard SEAS ’24).
Watching an object smaller than a penny levitate for a moment might not have “looked like much” to the average person, says Schafer, but it marked a pivotal moment for his yearslong research into whether it was possible to power flight in the Earth’s stratosphere using only sunlight.
Recently, Schafer sat down with the Harvard Innovation Labs to discuss how the idea for solar-powered flight came about, his journey spinning out his PhD research into startup Rarefied Technologies, and a potential application for the technology in weather forecasting.
Unlocking critical data collection with a centuries-old physics mechanism
When Schafer came to the Harvard John A. Paulson School of Engineering and Applied Sciences for his PhD in applied physics, he was particularly interested in climate tech. He explained that one of the many ways scientists have researched how to prevent climate change involves injecting aerosols into the atmosphere to reflect the sun’s light away from the earth. When Schafer began his doctoral studies in 2018, he joined then-Harvard physicist David Keith’s research group, which was investigating using aerosols to reflect sunlight. However, these aerosols may have adverse effects on the stratosphere and are difficult to control.
A potential solution to these issues, Schafer said, was something called photophoresis – a phenomenon where small particles suspended in gas start to move when illuminated by a beam of light. Keith's research (Photophoretic levitation of engineered aerosols for geoengineering, 2010) showed a potential new application for photophoresis around “engineering aerosols to stay up in the atmosphere with more control than traditional aerosols.”
“That was one of the first times that anyone had proposed using photophoresis to sustain flight in the atmosphere,” said Schafer. “My question was, ‘Could we use this physics mechanism, photophoresis, to fly something bigger than an aerosol…big enough that you could actually loft a payload?’”
This question became the focus of Schafer’s PhD research, leading him to investigate whether larger objects could fly in the mesosphere – the third layer of Earth's atmosphere, located above the stratosphere and below the thermosphere – using only energy from sunlight and, if so, what types of commercial applications these sun-powered flying objects would have.
Regarding commercial applications, Schafer described the mesosphere as an untapped region of the atmosphere. Because the air is so thin, it’s “too high for planes and balloons, but too low for satellites.” However, being able to collect wind, temperature, and pressure data will fill a major gap in current weather models, enabling both private and public sector organizations to “better predict when there’s going to be catastrophic weather events,” Schafer said.
From prototype to company spinout
Schafer met his co-founder Angela Feldhaus, a fellow Harvard SEAS PhD candidate, in 2019 while doing their PhDs as part of The Keith Group. Feldhaus thought from the beginning that their research had significant commercial potential, but Schafer wasn’t ready to begin exploring commercialization.
"It took me longer to get on board with it being a startup-level idea,” Schafer said. “After a couple more years of research and development, in 2021, we were making prototype devices in the clean room at Harvard’s Center for Nanoscale Systems. At that point, I was ready. In 2022 and 2023, we started accessing the Harvard Innovation Labs resources.”
In 2024, Schafer finished his PhD and licensed the two patents he wrote as a grad student from Harvard’s Office of Technology Development. Over the last year, Schafer and Feldhaus set up a second office for Rarefied in New Mexico, which offers the ideal atmospheric conditions for conducting their first field demonstrations.
In 2025, Schafer published a paper in Nature, "Photophoretic flight of perforated structures in near-space conditions." The paper details how Rarefied has “for the first time, made a structure that’s macroscopic and flies using less than the intensity of sunlight, which was a big proof of concept showing that we could fly in the upper atmosphere.”
Support fueling innovation
As Rarefied prepares to launch its first prototypes into the stratosphere in the coming year, Schafer says funding, mentorship, and resources from the Harvard Innovation Labs and the Harvard Grid played a crucial role in helping Rarefied achieve its technological breakthroughs.
“Funding-wise, we've received a significant part of our financial support through LEEP fellowships, with mine coming from Los Alamos National Laboratory and Angela’s from the Argonne National Laboratory,” says Schafer. “Additionally, we got a large grant through Breakthrough Energy, one of Bill Gates’ philanthropic programs for investing in tech that could abate and mitigate carbon emissions.”
At Harvard, Rarefied participated in the Harvard Climate Circle accelerator, received an award from the Harvard GRID, and was recognized with the i-lab's Ingenuity Award at the 2024 Harvard President’s Innovation Challenge. Beyond funding, he’s thankful for the advice and mentorship he received from Paul Hayre, executive director at the Harvard GRID, and Phil Green, senior advisor of B2B and tech at the Harvard Innovation Labs. “Those two have been awesome in helping us move along since the beginning,” he said.
From researcher to entrepreneur
It’s been nearly three years since Schafer started accessing startup support resources at Harvard to help turn his PhD work into a venture. Looking back on his transition from researcher to entrepreneur, he says he couldn't have done it alone.
“When you’re in the lab, you don’t have a good idea about how the research you're working on could be used. Other people will. Getting out of the lab and talking to people is critical to get the ball rolling, and the i-lab’s resources and connections helped a ton.”
And when it comes to identifying commercial applications for his technology, he says he’s had to de-program his expectations to get into the mindset of good customer discovery, adding it's critical to “talk to people you think this could be useful for, and then really listen – don’t come in with your own biases.”
These potential customers include government agencies and corporate partners who are eager to see Rarefied move towards commercialization.
