Scientists Unveil Wild New Way to Explore the Edge of Space
A Nature paper published today presents a proof-of-concept for an extremely lightweight, disc-like structure that levitates thanks to sunlight, no fuel required. Crafted from ceramic aluminum with a chromium base, the device floats on photophoresis, which literally means 'light-driven motion.' When sunlight strikes the device, the differences in heat and pressure around the disc create an upward airflow, keeping the disc airborne. The pressure difference produces photophoretic lift—enough to keep these little guys aloft.
Although this particular device was tailored for mesospheric exploration, the physics driving its flight could easily be applied to future missions beyond Earth—including the achingly thin Martian atmosphere, as long as there's sufficient sunlight, the researchers say.
'Photophoresis requires no fuel, batteries, or photovoltaics, so it is an inherently sustainable flight mechanism,' Ben Schafer, study lead author and an associate researcher at Harvard University, told Gizmodo in an email. 'We could use these devices to collect groundbreaking atmospheric data to benefit meteorology, perform telecommunications, and predict space weather.'
The initial idea dates back to 1873, when physicist William Crookes invented a radiometer that fed off sunlight. Subsequent projects attempted to build on Crookes's invention, but with limited success, as Igor Bargatin, a mechanical engineer at the University of Pennsylvania, explained in an accompanying News & Views article. (Although Bargatin did not participate in the new study, Schafer cited his work as one of the main inspirations for the device.)
Schafer and his colleagues, however, capitalized on previous work and recent advances in nanofabrication technology for their blueprint, constructing samples of 'shiny, thin squares with very tiny holes,' as Schafer described them. Researchers from multiple countries teamed up on the project, combining theoretical and experimental steps. Normally, the photophoretic force is weak relative to an object's size and weight, making it nearly impossible to notice, Schafer explained.
But the new device is so thin and tiny—about half the size of a penny—that the photophoretic force actually exceeds its weight, causing it to levitate. To validate its calculations, the team built a low-pressure chamber in the lab to simulate the atmospheric and sunlight conditions of the mesosphere. To their delight, the tiny discs remained aloft.
Schafer, now CEO of Rarefied Technologies, is moving quickly to bring these devices to commercial use. His team wants to tinker with the fabrication element so the discs can carry communications technology that can collect and send back weather data, Schafer said. 'We plan to use passive devices that can be tracked remotely with lidar or radar to collect weather data in the upper atmosphere; this could reach the pilot phase in a couple years,' he explained.
'If the full potential of this technology can be realized, swarms or arrays of such photophoretic flyers could be collecting high-resolution data on the temperature, pressure, chemical composition, and wind dynamics of the mesosphere,' Bargatin added. 'What began as a Victorian curiosity might soon become a key tool for probing the most elusive region of the atmosphere.'
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