Propulsion of Porous Plates in Thin Atmospheres by Temperature Fields: Experiments on Parabolic Flights

In low pressure environments macroscopic bodies can be subject to photo- and thermophoretic motion if temperature gradients are present. Porosity can increase the efficiency of this propulsion. We developed a setup to generate a temperature field and measure phoretic accelerations in a parabolic flight. In a first campaign we studied the pressure dependence of the acceleration for thin plates (1.7 mm thickness, 2.2 and 3.5 cm diameter) consisting of sintered glass spheres of a size range of 150 to 250 μ m and 40 to 70 μ m. We find evidence for two characteristic propulsion maxima at pressures related to the overall size of the plate as well as the bead (pore) size. The increase of the magnitude of acceleration due to the porosity is on the order of 10 −2 g for the specific samples. This force is comparable to the phoretic force attributed to the overall size of the plate.