Photophoretic Tracers for Near-Space Remote Sensing at 30-100 km Altitudes 

Benjamin Schafer
Rarified Technologies, Inc.

We propose a new approach to atmospheric sensing at 30-100 km altitudes using photophoretically levitating tracers. These lightweight structures harness sunlight to remain suspended for up to months at controlled altitudes and can be remotely tracked by satellite-based lidar or radar. Unlike natural aerosols, these tracers are designed to provide strong and tunable backscatter at standard remote sensing wavelengths, enabling passive, persistent, and altitude-selective measurements of wind, temperature, and pressure in a region that is critically under-measured by existing systems.  

This concept addresses a major gap in current sensing capabilities. The mesosphere and upper stratosphere play a key role in atmospheric dynamics, space-domain awareness, space weather, and high-altitude platform navigation. Despite the importance of this region, data collection remains a challenge. Near-space is too high for sustained balloon flight and too low for satellites to orbit. Concentrations of extant atmospheric species are also too low for remote sensing techniques such as lidar and radar. Photophoretic tracers offer a new solution: a persistent, stratified sensor layer of non-toxic, inert backscattering points that require no onboard power, propulsion, or control. These tracers can be deployed via high-altitude balloons or rockets and autonomously reach their target altitudes based on their geometry and coatings.  

In a representative mission, thousands of tracers are released from a lightweight balloon at around 30 km. The tracers rise to their target altitude of 90-100 km, the lower ionosphere. Satellite-based lidar tracks their motion over their month-long lifetimes. Tracer trajectories enable continuous mapping of wind shear, thermal gradients, and pressure profiles at sub-kilometer resolution and hourly cadence. The collected real-time data are used to calibrate boundary conditions of ionospheric space weather models. As more data is collected, the predictive capabilities of these models improve, leading to enhanced situational awareness and communications resilience in near-space and LEO. Other early deployments could, for example, support weather model improvements in the tropics and monitor atmospheric conditions over spaceports.  

This work builds on emerging experimental results in photophoretic flight, with laboratory validation of levitation in near-space conditions and initial simulations of tracer dispersion and visibility. Backscatter models confirm feasibility for orbital detection using commercially available lidar systems. The tracers are designed to safely disintegrate at end-of-life and are compatible with scalable fabrication techniques. By engineering the scattering medium itself, this concept inverts traditional atmospheric remote sensing. It enables lower-SWaP-C satellite sensing systems and a fundamentally new class of persistent measurement tools for national security, meteorology, heliophysics, and planetary exploration.  

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Loura Hall

Actively Steerable Femtosat Constellations for In-situ Exploration of Saturn’s Rings, Atmosphere, and Magnetosphere

Michael Rubenstein
Northwestern University, Chicago

We propose a mission to use ~10,000 actively steerable femtosats to map the ring composition, atmospheric composition and density, and the magnetic field distribution of Saturn. Conducting in-situ surveys of Saturn’s rings with a single flagship mission, such as Cassini, would carry an unacceptably high risk of mission failure due to particle collisions. However, the distributed nature of the proposed mission means it can accept a risk that could destroy many of femtosats in the constellation, making in-situ survey of the ring possible.  

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PRAXIS: Planetary Rings Autonomous EXploration with In-situ Sampling

Marco Quadrelli
NASA Jet Propulsion Laboratory

Humanity has never touched the particles of a planetary ring, but if we were able to get close enough and sample them, it will transform understanding of ring structure and origins for Saturn (dense), Uranus and Neptune (tenuous), rings of other objects such as Centaurs Chariklo and Chiron, and even early protoplanetary and circumstellar disks. Despite Cassini’s groundbreaking discoveries, fundamental questions about the formation, dynamics, and evolution of planetary rings remain unanswered. After Cassini, there is a very strong scientific case to learn more about the microphysical interactions of Saturn’s rings, and this necessitates sampling them. Many ring structures and features such as self-gravity wakes, “propellers”, density waves and gap edges remain to be explored at high resolution. Saturn’s rings are micron-size grains to house-size boulders, always in motion. They are made mostly of water ice, piles of rubble coming together and breaking apart. PRAXIS addresses a key Decadal priority by delivering the first direct observations of mm- to cm-scale ring particles, a capability Cassini lacked. Planetary rings are highly dynamic environments where constant particle motion demands advanced robotic autonomy for collision avoidance, precision sampling, and in situ analysis. Our system adapts innovations from sport casting to capture free-floating particles, and instrument miniaturization for real-time analysis. AI integration enables the first-ever autonomous collection of ring particles, directly measuring science priorities like particle size, porosity, and composition. PRAXIS develops and tests a novel AI-driven, bio-inspired robotic explorer to perform in situ ring sampling, a capability never before attempted. This effort directly supports Decadal Survey priorities in planetary ring science while spearheading the next generation of planetary robotic exploration and delivering transformative insights into the origins and evolution of ring systems. Feasibility of PRAXIS is already on firm ground because it leverages key element of the Saturn Ring Observer Mission Study, which considered an orbit grazing the rings and hovering above them to directly image the ring particles in motion. After an initial imaging and characterization phase to select the ring particle, the spacecraft conducts a touch-and-go sampling event of the particle surface with a long and soft deployable boom. Since the particles are always in motion within the ring, there is a compelling case for the spacecraft staying away to avoid collision, hence the agile sampling with the long boom is justified. Once the sample is retrieved, the PRAXIS exploration system moves to another section (or gap) of the rings, thus sampling many diverse regions. Feasibility of PRAXIS will be demonstrated Phase I with simulation and sound system design, motivating solid system design and development of a physical prototype in Phase II. The system’s versatility makes it valuable across planetary formation missions, positioning it for infusion into the upcoming Uranus Probe mission. 

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ECLIPSE – Efficient variable Conductivity Lunar Insulator for Passive Surveyor Environmental control

Austin Phoenix

Virginia Polytechnic Institute & State

A disaggregated lunar infrastructure requires novel thermal management methods to enable future lunar operations. While thermal management solutions exist for large infrastructure, the smaller mobile systems that operate independently require improved temperature regulation devices that can survive without heaters or substantial power requirements, while limiting stress-inducing temperature fluctuations. New material solutions can passively regulate the flow of thermal energy to enable small devices to survive the extremes of the lunar environment without relying on external infrastructure. The Variable Thermal Conductivity Metamaterial (VTCM) outperforms other VTCMs and can be designed to act as an advanced mechanical thermal switch. Variable internal contact is used to regulate the flow of energy to the radiator passively. The design of the metamaterial’s internal geometry, material selection, and the passive shape memory alloy actuation system can achieve an arbitrary thermal conductivity as a function of temperature using internal mechanical contact. The metamaterial concept begins in a low temperature state with no initial contact and a corresponding low conductivity state. As the temperature of the metamaterial increases, partial SMA actuation induces partial contact internal to the metamaterial, resulting in an increase in conductivity. As the temperature continues to increase, the contact area increases until full contact is achieved. This metamaterial enables the design of an arbitrary thermal conductivity as a function of temperature by designing the thermal pathways’ cross-sectional area and length. The proposed work will use the variable thermal conductivity metamaterial, capable of passive thermal control, to enable mobile autonomous surveyors that can perform extended lunar operations while minimizing Size, Weight, Power, and Cost (SWaP-C).

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Loura Hall

Why Maine’s Sandy Shorelines Turn Jagged

The Wabanaki people have a deep well of creation myths explaining the rocky coastlines of the Bay of Fundy, Downeast Maine, and Acadia National Park. Many involve Glooscap—a magical figure said to have floated down the Bay of Fundy in a stone canoe, sculpting coastal features by scraping the vessel across the landscape and scattering enormous boulders during battles with primordial beavers, frogs, moose, whales, and other gigantic animals.

Fewer Indigenous creation myths survive to explain the origins of the sandy and marshy shorelines of southern Maine and the rocky, indented coasts of the state’s Midcoast region. But the sharp contrast between the sandy shoals and beaches south of Portland and the rocky shoreline of promontories, headlands, and narrow peninsulas to the east—visible in the Landsat image above—has long drawn the attention of coastal geologists, whose scientific explanations on its origins abound.

The coastal transition reflects both differences in the underlying bedrock and the distribution of sediment left behind by the last glacial maximum, coastal geologists say. Southern Maine has broad deposits of sand, much of it sourced from rivers. The sandy beaches of Saco Bay, for instance, home to Maine’s longest contiguous beach and the state’s largest saltmarsh, received sediment from the weathering and breakdown of the White Mountains, with material transported to the coast largely by the Saco River, explained Peter Slovinsky, a geologist with the Maine Geological Survey. Waves and tides reworked these soft sediments over time, sculpting them into the arch-shaped embayed beaches and sprawling salt marshes found around Saco Bay and the broader region.

While erosion-resistant granite juts from the sandy shorelines in southern Maine to form rocky headlands, metamorphic bedrock becomes the dominant surface feature east of Portland. There, whole ridges and valleys made of rock layers transformed by exposure to high pressures and temperatures define the landscape. During the last ice age, glaciers scoured and widened many of these coastal valleys, which later flooded as the Laurentide Ice Sheet melted and sea levels rose.

Around Casco Bay, these ridge-and-valley systems, combined with the drowning of the shoreline, produce the jagged, highly indented shoreline and many long, narrow islands seen today. “The tortured folds of these old landscapes also set up a sharp directional preference for erosion to exploit,” said Nicholas Whiteman, also a geologist with the Maine Geological Survey. “This led to the eye-catching difference in the orientation of the islands and necks that dominate Casco Bay compared with those to the northeast.”

The various forms that coastlines take fascinate geologists, but they also carry everyday implications for the economies of Maine’s coastal communities. While tourists flock to the sandy beaches of communities like Saco and Kennebunkport, the state’s iconic lobster fisheries are concentrated in Midcoast Maine. The crustaceans thrive in the cold waters of the region’s many rocky, protected inlets, turning communities such as Harpswell into leaders in lobster landings.  

The state’s oyster farms are also concentrated in this region. Casco Bay and the Damariscotta Estuary, sheltered from winds and waves, offer waters that farmers can easily access without large boats. These waters provide a range of temperatures, salinities, and other characteristics that create numerous microclimates where oysters can grow quickly and take on a variety of tastes, known as merroir, explained Tom Kiffney, a researcher at the University of Maine. Kiffney is part of a team of researchers using Landsat and other satellite observations to predict oyster growth rates and help identify the most promising locations for new oyster farms in Maine based on water temperatures and quality.

NASA Earth Observatory image by Michala Garrison, using Landsat data from the U.S. Geological Survey. Story by Adam Voiland.

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August 31, 2025

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References & Resources

• Kelley, J. (1987) An Inventory of Coastal Environments and Classification of Maine’s Glaciated Shoreline. Glaciated Coasts, 151-176.
• Kiffney, T., et al. (2026) Using dynamic energy budget modeling and high-resolution satellite products to predict eastern oyster growth at a farm scale. Aquaculture, 612(1), 743133.
• Leland, C. (1884) Algonquin Legends of New England: How Glooskap sailed through the great Cavern of Darkness. Accessed July 17, 2026.
• Maine.gov (2026) Maine’s Coastal Marine Geology. Accessed July 17, 2026.
• Maine Geological Survey (2002) Simplified Bedrock Geologic Map of Maine. Accessed July 17, 2026.
• Maine Geological Survey (1999) The Variety of Maine’s Changing Shoreline. Accessed July 17, 2026.
• Merroir (2026) What is Merroir? Accessed July 17, 2026.
• NASA (2026, January 15) NASA Data Helps Maine Oyster Farmers Choose Where to Grow. Accessed July 17, 2026.
• NASA Earth Observatory (2017) Oyster Prospecting With Landsat 8. Accessed July 17, 2026.
• Snyder, J., et al. (2017) Oyster Aquaculture Site Selection Using Landsat 8-Derived Sea Surface Temperature, Turbidity, and Chlorophyll a. Frontiers in Marine Science, 4(190).
• World History Encyclopedia (2025, February 6) Glooscap Tales. Accessed July 17, 2026.

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