Scientists often call the mesosphere as “the ignorosphere” – a region too high for the planes or the meteorological balloons to explore, but too low for the satellites to be surveyed. Despite our technological advances, we have not yet found a decent means of monitoring this large range of air, which is around 37 miles (60 kilometers) above the surface. But the engineers turn to a solution – an inspired by an invention similar to a 19th century toy.
An article of nature published today presents proof of concept for an extremely light disk structure which levite thanks to sunlight, no required fuel. Made from ceramic aluminum with a chrome base, the device floats on photophoresis, which literally means “light movement”. When sunlight strikes the device, differences in heat and pressure around the disc create an ascending air flow, keeping the disc in the air. The pressure difference produces a photophoretic elevator – enough to keep these little guys at altitude.
Although this particular device has been adapted to mesospheric exploration, physics leading its flight could easily be applied to future missions beyond the earth, including the painful Martian atmosphere, as long as there is enough sun, according to researchers.
“The photophoresis does not require fuel, batteries or photovoltaic, it is therefore an intrinsically sustainable flight mechanism,” said Ben Schafer, principal of the study and associate researcher at Harvard University, in Gizmodo in an e-mail. “We could use these devices to collect revolutionary atmospheric data for the benefit of meteorology, perform telecommunications and predict space weather.”
The initial idea dates back to 1873, when the physicist William Crookes invented a radiometer that fed the sunlight. Subsequent projects have attempted to rely on the invention of Crookes, but with limited success, such as Igor Bargatin, mechanical engineer at the University of Pennsylvania, in a news & views support article. (Although Bargatin did not participate in the new study, Schafer cited his work as one of the main inspirations of the aircraft.)
Schafer and his colleagues, however, have capitalized on previous work and recent advances in nanofabrication technology for their plan, building samples of “shiny thin squares with very small holes”, as Schafer described them. Researchers from several countries have teamed up with the project, combining theoretical and experimental stages. Normally, the photophoretical force is low compared to the size and weight of an object, which makes it almost impossible to notice, explained Schafer.
But the new device is so thin and tiny – about half the size of a penny – that the photophoretic force actually exceeds its weight, which makes it levitate. To validate its calculations, the team has built a low pressure chamber in the laboratory to simulate the atmospheric conditions and the Sun of the Mesosphere. To their greatest pleasure, the tiny discs remained in the air.
Schafer, now CEO of Rarefied Technologies, moves quickly to put these devices for commercial use. His team wants to tinker with the manufacturing element so that the discs can transport communication technologies that can collect and return meteorological data, said Schafer. “We plan to use passive devices that can be followed remotely with the LIDAR or the radar to collect meteorological data in the upper atmosphere; this could reach the pilot phase in a few years,” he explained.
“If the full potential of this technology can be carried out, swarms or tables of these photophoretic leaflets could collect high resolution data on temperature, pressure, chemical composition and the dynamics of the mesosphere wind,” added the bargatine. “What started as a Victorian curiosity could soon become a key tool to probe the most elusive region of the atmosphere.”
