A hot-film anemometer has been developed for the Beagle 2 Mars lander. The sensor returns wind speed (up to 30 m/s) and horizontal component of wind direction. The wind sensor is simpler and lighter than previous wind sensors, with a total mass of only 15 g including electronics, and a total power consumption of only 250 mW.
Three hot platinum films are equally spaced around the circumference of a vertical cylinder. A known current is dissipated in each film, heating the film to 50 - 100 °C above the ambient gas temperature. The film temperature is obtained by measuring its resistance. An effective heat transfer coefficient is then calculated for each film. These coefficients can in turn be related to the overall wind vector at the sensor.
The wind sensor's position at the end of Beagle 2's motorised arm allows several new possibilities for wind measurement on Mars that were unavailable in previous missions. The height of the wind sensor can be adjusted to any height between ~20 cm and ~110 cm above the lander body, or can be moved laterally at a given height to study the effects of lander interference.
The wind sensor was calibrated in a new wind tunnel facility, in which Martian surface wind conditions are simulated. Wind speeds of 0 - 60 m/s can be created in a CO2 atmosphere at pressures of 5 - 10 mbar. A cooling system which would allow wind tunnel operation at Martian temperatures (160 - 300 K) may be installed for future calibrations.
The above text is a modified version of the abstract of a poster presented at DPS annual meeting, Nov 2001, New Orleans.
Authors: C. F. Wilson & S. B. Calcutt, AOPP, Oxford University; T. V. Jones & M. G. Oldfield, Engineering Science, Oxford University.
Measuring wind on Mars: an overview of in situ sensing techniques. Presented at DPS meeting in Cambridge, September 2005.
Hi-res photo of B2WS in place on PAW
Lo-res photos of B2WS integrated into Beagle 2 lander. photo 1, photo 2, photo 3
IR camera footage showing heating and cooling of sensor Note this at Earth atmospheric pressure, with no wind.
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