Part of the Phoenix lander showing the Telltale on top of the Meteorological Mast ©NASA/JPL

The Phoenix Lander

Phoenix landed close to the North Pole of Mars on May 25, 2008. In this region, ice has been detected in the soil by means on gamma ray spectrometer (GRS) on Mars Oddyssey. The lander will dig for samples and deliver them to various chemistry experiments on the lander deck. Having crude information on the wind cycle at the landing site, it is possible to select times for delivery of samples, where the dust is not blown away in the wind.
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Picture of the Telltale delivered to NASA

The Telltale

The Telltale consists of a gallows that is mounted on the top of the Meteorological Mast of the Lander. The active element of the instrument is an extremely lightweight Kapton tube hanging in Kevlar fibres. Images taken of the instrument will show the deflection of the Telltale due to the wind. A mirror is mounted below the active part to enable better direction information.
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Previous version of the Telltale mounted on the meteorological mast for vibration testing in Ottawa in may 2006. The telltale failed this test completely

Development of the Telltale

The air pressure on Mars is less that 1% of the Earths, and this means that the instrument had to be extremely sensitive. The forces due to the wind are of the order of few millionths part of a Newton (The instrument weighs 20 grams, meaning that the gravitational pull is 0.2 Newton ). This was accomplished by making the active part of the instrument as lightweight as possible (about 10 thousands of a gram). After intensive testing to document that the experiment would survive the launch and landing vibrations, it was calibrated in the Wind tunnel at the Mars Simulation Laboratory
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