Low pressure spherical thermal anemometer for space missions

Abstract

The novelty of this 2D thermal anemometer is the spherical compact and robust design with improved sensitivity in the range of 600-900Pa of carbon dioxide pressure and 0.25 to 10 m/s wind speed. The small size (11.2mm diameter) and unprecedented 3D printing fabrication of a low emissivity silver shell allows to place inside of the sphere the platinum heating and sensing resistors. It improves the performances of the Viking, Pathfinder and Curiosity wind sensors for the surface of Mars. The conduction losses to the support are largely suppressed by also heating the insertion point at the same temperature than the shell Overall, the convection power to the ambient is in the range of 30mW per 10K of overheat respect to the ambient, which is about the 68% of the total power. Splitting the spherical shell into two hemispheres provides angular sensitivity and the wind direction is found from the convection power differences between them. The concept can be easily extended to three-dimensional sensing by using three of these sensors in different planes. It can also be applied to aeronautical engines such as stratospheric balloons.