Photophoretic Levitation of Micron and Millimeter-scale Nanofabricated Structures for Geoengineering

The photophoretic force could be used to stably levitate ultrathin micron and millimeter-scale structures in the atmosphere without onboard power systems. Among their uses for many atmospheric applications, these structures show potential as artificial reflectors of solar insolation for solar radiation management (SRM). Candidate structural designs for levitation, the diurnal lofting force on these structures, and optimization of their thermal, radiative, and structural parameters for maximum lofting force are discussed. Levitation is only possible in the free molecular flow regime. Hence, isothermal designs with small characteristic length scales that maximize surface area prove highly effective at lofting payloads many times their weight near both the stratopause and mesopause. Macroscopic, non-isothermal structures with channels, such as "nanocardboard," benefit from no fundamental size limit at high altitudes and additional levitating thrust via thermal transpiration, as recently demonstrated in practice. Discussion will focus on functionalized embodiments to act as fleets of reflectors, geoengineering performance, deployment methods, and atmospheric location control.