A New Window into Earth’s Higher Environment

Key takeaways

• Harvard SEAS researchers have examined and validated light-weight nanofabricated constructions that may passively float within the mesophere, which is about 45 miles above Earth’s floor.
• The units levitate through photophoresis, or sunlight-driven propulsion, which happens within the low-pressure circumstances of the higher environment.
• Such constructions could possibly be used for sensing and communication in an space of the environment that’s been tough to observe with current expertise.

Between 50 and 100 kilometers (30-60 miles) above Earth’s floor lies a largely unstudied stretch of the environment, known as the mesosphere. It’s too excessive for airplanes and climate balloons, too low for satellites, and practically unattainable to observe with current expertise. But understanding this layer of the environment might enhance the accuracy of climate forecasts and local weather fashions.

A brand new examine published in Nature by researchers on the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS), University of Chicago, and others introduces a novel strategy to attain this unexplored near-space zone: light-weight flying constructions that may float utilizing nothing however daylight.

“We are studying this strange physics mechanism called photophoresis and its ability to levitate very lightweight objects when you shine light on them,” stated Ben Schafer, lead creator of the paper and a former Harvard graduate scholar within the analysis teams of Joost Vlassak, the Abbott and James Lawrence Professor of Materials Engineering at SEAS, and David Keith, now a professor on the University of Chicago. 

How photophoresis works

Photophoresis happens when gasoline molecules bounce extra forcefully off the nice and cozy aspect of an object than the cool aspect, creating steady momentum and carry. This impact solely occurs in excessive low-pressure environments, that are precisely the circumstances discovered within the mesosphere.

The researchers constructed skinny, centimeter-scale membranes from ceramic alumina, with a layer of chromium on the underside to soak up daylight. When gentle hits this construction, the warmth distinction between the highest and backside surfaces initiates a photophoretic lifting pressure, which exceeds the construction’s weight.

“This phenomenon is usually so weak relative to the size and weight of the object it’s acting on that we usually don’t notice it,” Schafer stated. “However, we’re in a position to make our constructions so light-weight that the photophoretic pressure is greater than their weight, so that they fly.

The idea originated greater than a decade in the past when Keith hypothesized completely different makes use of of photophoretic particles, together with their potential to scale back local weather warming. A collaboration started with then-graduate scholar Schafer, and Vlassak, an knowledgeable in nanofabrication and experimental mechanics, in an effort to assist transfer the ideas from principle to actuality.

The collaboration turned possible via latest advances in nanofabrication expertise, which permit researchers to construct low-mass, nanoscale units with higher precision.

“We developed a nanofabrication process that can be scaled to tens of centimeters,” Vlassak stated. “These devices are quite resilient and have unusual mechanical behavior for sandwich structures. We are currently working on methods to incorporate functional payloads into the devices.”

Testing units within the lab

Using these fabrication strategies, the analysis workforce created centimeter-scale constructions and straight measured the photophoretic forces appearing on them inside a low-pressure chamber Schafer and former Harvard postdoctoral fellow Jong-hyoung Kim inbuilt Vlassak’s lab. They in contrast these outcomes to predictions of how such constructions would behave within the higher environment. Device design and fabrication have been led by Kim, who’s now a professor at Pukyong National University in South Korea. 

“This paper is both theoretical and experimental in the sense that we reimagined how this force is calculated on real devices and then validated those forces by applying measurements to real-world conditions,” Schafer stated. 

A key experiment detailed within the paper reveals a 1-centimeter-wide construction levitating at an air strain of 26.7 Pascals when uncovered to gentle at simply 55% the depth of daylight. This strain situation fashions what’s discovered 60 kilometers above the Earth’s floor.

“This is the first time anyone has shown that you can build larger photophoretic structures and actually make them fly in the atmosphere,” stated Keith. “It opens up an entirely new class of device: one that’s passive, sunlight-powered, and uniquely suited to explore our upper atmosphere. Later they might fly on Mars or other planets.”

Possible purposes: Sensing, communication, Martian exploration

The workforce envisions a variety of attainable purposes for his or her new machine, particularly in local weather science. If outfitted with light-weight sensors, this machine might gather key information like wind velocity, strain, and temperature from a area of the environment that has lengthy remained a blind spot. This information is crucial for calibrating the local weather fashions that construct the inspiration of climate forecasting and local weather change projections.

Other potential purposes embody telecommunications for protection and emergency response eventualities. Using a fleet of those units might allow a floating array of antennas with information transmission capabilities corresponding to low orbit satellites like Starlink, however with decrease latency because of their nearer proximity to the bottom.

Since Earth’s higher environment shares key traits with the skinny environment of Mars, the machine might facilitate new modes of planetary exploration and communication in that setting as effectively.

The workforce’s subsequent step is to combine onboard communications payloads that may permit the machine to transmit real-time information throughout flight. 

“I think what makes this research fun is that the technology could be used to explore an entirely unexplored region of the atmosphere. Previously, nothing could sustainably fly up there,” Schafer stated. “It’s a bit just like the Wild West when it comes to utilized physics.”