Tiny devices propelled by sunlight could explore a mysterious region of Earth’s atmosphere
The auto-lof devices powered by sunlight have been tested for the first time in conditions close to vacuum similar to those of the upper atmosphere of the earth, opening the way to a revolution in atmospheric science.
The tiny light membranes – which are made of aluminum oxide and a layer of chrome – take advantage of a phenomenon known as photophoresis, which occurs when a side of a slim material becomes warmer than the other. While the gas molecules bounce on the warmer side, they push the membrane upwards. However, the effect is very low and can therefore only be observed in very low pressure environments, such as those close to the edge of space.
In the recent experience, described in an article published on August 13 in the journal Nature, the researchers made stains 0.4 inch wide (1 centimeter) in a vacuum chamber when exposed to light about 55% as intense as natural sun.
“It is a great result showing that it would really work in the same conditions that you have in the upper atmosphere,” said Ben Schafer, main author of the newspaper and researcher at Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS).
“We speak [about a] Atmosphere region which is sometimes called the ignorosphere, because nothing can fly. Being able to send something there would allow us to take much more precise data than we can currently, “he told Space.com.
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The ignorosphere includes the mesosphere – the layer of the earth’s atmosphere at altitudes between 30 and 53 miles (50 to 85 kilometers) – plus a section of the thermosphere to an altitude of 100 miles (160 km). The ignorosphere is too high for planes to reach, but too low for instruments on board satellites on Lower Terrace to sample. The sensors placed on sound rockets make occasional measures in the region, but most of the processes that take place there are little understood.
The Ignorosphere forms a border between the gas shroud of the earth and space. When the coronal mass ejections – vast evictions of plasma in charge of the sun – struck the earth, they deposit most of their energy in the ignorosphere. Auroral gleams occur in the ignorosphere, as well as the energetic exchanges which lead to geomagnetic storms which can eliminate electrical networks and throw satellites from their orbits. These unexplored altitudes are also the place where satellites burn when they return and where the air pollution produced during their incineration accumulates.
“Obtaining precise data from this region on winds, temperatures, pressures, etc. would really increase the accuracy of existing global climate models,” said Schafer. “It would fill this shortcoming that we have.”
Shafer and her colleague Angela Feldhaus have turned a company from Harvard Seas called Rarefied Technologies. The goal of the startup is to conduct realistic atmospheric experiences with such devices in the hope of marketing them.
To lift miniature sensors and antennas in the ignorosphere, the membranes should be a little larger, about 2.4 inches (6 cm) wide. “It would be a disc that could loft around 10 milligrams [0.0004 ounce] In the near space, “said Schafer.
The devices would be released from a stratospheric ball at around 30 miles (50 km) above the earth. From there, they were walking at altitudes up to 60 miles (100 km), where they would stay during the day. At night, the devices sank into the atmosphere, but if they were quite light, would not fall back on earth and go up after sunrise, said Schafer.
Researchers want to focus on improving the material and its structure to reduce its weight, which would make larger devices possible.
Rely on previous ideas
The photophoresis was discovered in the 19th century but remained mainly neglected until recently. The progress of the science of nanofabrication materials and technologies in the past two decades have finally made it possible to contemplate its practical applications.
Schafer and his colleagues were inspired by a theoretical article by David Keith, then professor of physics applied to Seas and now at the University of Chicago. Keith proposed that reflective membranes propelled by photophoresis could be used as geoengineering intervention to reduce the temperature of the earth if the world did not contain climate change by reducing its carbon emissions.
Keith supervised Schafer’s work until 2023.
“This is the first time that anyone has shown that you can build larger photophoretic structures and have them fly in the atmosphere,” Keith said in a statement. “It opens a whole new class of device: that passive, fueled by sunlight and uniquely to explore our high atmosphere.”
Schafer thinks that technology could find many uses. This could help study the thin atmosphere of March or even to compete with the megaconstellations of high speed satellite of SpaceX.
“If you were to put small communication packages on board these things and put them in the mesosphere, you could actually compete with constellation data flow rates,” said Schafer.
He admitted that the devices should become a little lighter and larger to accommodate useful communication charges and large-scale navigation units to maintain a stable position above fixed spots on earth.
