MEAM Ph.D. Thesis Defense: “Enhancing Photophoretic Levitation using Three-dimensional Structures for Flight in the Mesosphere and on Mars”

Current propulsion and flight mechanisms limit atmospheric observations. The mesosphere is too dense for satellites and too thin for typical planes and balloons, with similar conditions found in the Martian atmosphere, especially at Olympus Mons. Photophoresis, the movement of gas molecules due to light, has been studied for microscale objects like aerosols and operates optimally within the pressure ranges of these regions. When applied to ultrathin, ultralight macroscale objects, levitation occurs. These objects, such as plates and disks with microstructures, absorb visible light and heat up. The resulting temperature changes pump gas molecules through microchannels and cause a recoil force from molecules striking the hotter surface. These combined effects produce enough force to levitate centimeter-scale objects with no moving parts and only light. We designed photophoretic aircraft with 3D hollow geometries to pump ambient air through sidewalls, creating a high-speed jet. Simulations and parametric studies optimized these geometries, showing potential for kilogram-scale payloads for meter-scale aircraft 50 to 80 km above Earth’s surface. This included a novel theoretical framework based on previous 2D plates but expanded to 3D structures. We also fabricated millimeter-scale versions using microfabrication methods to experimentally investigate levitation in vacuum chamber experiments. Furthermore, we developed a scalable manufacturing method for a different photophoretic aircraft with enhanced temperature gradient-induced levitation of 3D geometries made of a Mylar sandwich composite alongside a new experimental method to measure and compare photophoretic forces of solid versus porous objects. Finally, we explored solar buoyancy, through theory and experimental developments, to transport the structures to the mesosphere and discussed their potential applications for carrying sensors to measure GPS and state properties in situ. Applications of this work include atmospheric science missions in the mesosphere and on Mars in collaboration with NASA.