Their simulations estimate that a 6-centimeter plate could carry 10 milligrams of cargo in the mesosphere under natural sunlight. Ten milligrams may not sound like much; a drop of water weighs five times as much. But technological advancements have reduced silicon chips to dust-sized sensors much smaller than that. These “smart dust” systems fit into a power source, radio communications, and data collection sensor in cubes just a millimeter wide. “There is a lot that researchers can do if you give them a cubic millimeter of silicon,” Bargatin says. “And a cubic millimeter of silicon weighs a few milligrams.”
In their vacuum chamber test, they found that when the light intensity swung past the power of sunlight, that extra flow of energy carried the flyer higher. But after about 30 seconds, the disc started to curl up due to photophoretic force and eventually collapse. Ultrathin Mylar is very thin on its own, Bargatin says. The carbon nanotube shag makes the Mylar disk stiffer, but the force of high-speed molecular collisions eventually jam the flyer. The team’s model can predict what disc sizes, air pressure, and light intensities will cause this, and Bargatin says work is underway to develop a lightweight frame.
Bargatin envisions researchers one day releasing sensor-laden gliders into the mesosphere and letting them roam like weather balloons or floating ocean sensors. “Another approach is to develop truly smart flyers that can control where they go,” he says. The same tilt that stabilizes the levitators could be used to steer them. And, he adds, hanging the sensor on the levitator like a parachuter hanging from a canopy would help keep the system upright when faced with wind.
Still, Marsh is not convinced that such a device could withstand mesospheric conditions. “Any instrument will have to operate in the extreme conditions of the mesosphere, where the average wind can easily exceed 100 mph,” he writes. Winds in the upper mesosphere can be very shear, temperatures can drop to 140 degrees below zero, and space weather radiates through the mesosphere and can damage communication systems.
Paul Newman, chief Earth science scientist at NASA’s Goddard Space Flight Center, agrees that calculating mesospheric winds will be a major engineering challenge, but he can’t help but be delighted with the potential applications. “I actually think this is a really cool idea,” he says. One possibility would be to investigate water vapor in the mesosphere, where arctic clouds form so high that the sun still illuminates them at night. The mysterious clouds aren’t just beautiful, Newman says; their possible link with increased greenhouse gases means they are more common – but researchers can’t monitor the water content and temperature of the mesosphere as closely as they would like. Mesospheric clouds are “another sign of climate change. And we need information for that, ”says Newman. “Therefore, these can be very cool to get data on the atmospheric composition.”
Newman adds that the plates’ small character and levitation power could also be intriguing to Mars research. The barometric pressure of the Martian atmosphere is comparable to Earth’s mesosphere, so perhaps light autonomous levitators can collect temperature or composition measurements. “You can only take off once a day, go up and then come back down and land on your little Mars lander,” he imagines. “We don’t have that information on Mars. That would just be great. (NASA plans to test a small helicopter called Ingenuity as part of its soon-to-land Perseverance rover mission, but that craft will be much larger and is still in flight test phase; it’s not ready yet. scientific missions.)
Bargatin says they are currently investigating applications for Mars and that the team also hopes to make their microflyers work at sea level on Earth. But regardless of any use, Azadi will always remember seeing the Mylar creation floating for the first time, exactly according to his theoretical predictions. “Then,” he says, “I called my girlfriend and said,“ I think I’ll be graduating soon. “”
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