Low pressure spherical thermal anemometer for space missions

A novel spherically shaped thermal anemometer for low pressure, Mars-like conditions, is described. The concept has been designed using finite element multyphysics simulations to find out the thermal conductance to the ambient for varying conditions of wind speed and direction and ambient pressure and temperature. A prototype 1cm diameter suitable to work under these environment in the range 0.25-10m/s speed has been build using 3D printing and tested inside a low pressure chamber. The protopype shown has two separated hemispheres, independently heated above the ambient temperature, providing angle sensitivity in one plane. Measurements of the heating power in both hemispheres required to keep an overheat of 30K are shown as a function of the wind direction showing good sensitivity at 0.5m/s. One improvement of this sensor is the means provided to also heat the core of the sphere where the circuit board is located thereby avoiding most of the conduction losses to the supports. The concept is scalable to other wind speed and pressure conditions and also to full 3D measurements.