Towards photophoretically levitating macroscopic sensors in the stratosphere
Andrew Lockley
Towards photophoretically levitating macroscopic sensors in the stratosphere
Benjamin C. Schafer1,*, Jong-hyoung Kim1, Joost J. Vlassak1, David W. Keith1
Abstract
Photophoretic forces could levitate thin 10 centimeter-scale structures in Earth’s stratosphere indefinitely. We develop models of the thermal transpiration lofting force on a bilayer sandwich structure under stratospheric conditions driven by radiative fluxes in the thermal-infrared and solar-band. Similar structures have been levitated in the laboratory. Lofting is maximized when the layers are separated by an air gap equal to the mean free path (MFP), when about half of the layers’ surface area consists of holes with radii < MFP, and when the top layer is solartransmissive and infrared-emissive while the bottom layer is solar-absorptive and infraredtransmissive. We describe a preliminary design of a 10 cm diameter device that combines a levitating structure made of two membranes 2 µm apart with the support structure required for stiffness and orientation control. We limit the design to components that could be fabricated with available methods. Structural analysis suggests that the device would have sufficient strength to withstand forces that might be encountered in transport, deployment, and flight. Our models predict a payload capacity of about 300 mg at 25 km altitude and our analysis suggests it could support bidirectional radio communication at over 10 Mb/s and could have limited navigational abilities. Such devices could be useful for atmospheric science or telecommunications, and similar devices might be useful on Mars. Structures a few times larger might have payloads of a few grams.
[PDF] Towards photophoretically levitating macroscopic sensors in the stratosphere
stratosphere indefinitely. We develop models of the thermal transpiration lofting force
on a bilayer sandwich structure under stratospheric conditions driven by radiative …
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