An impact penetrometer for a landing spacecraft

The design, development and calibration of an impact force transducer or penetrometer, for use on the Huygens spacecraft scheduled to land on the surface of Saturn's moon Titan, is described, The thumb-sized transducer employs a piezoelectric sensing element and is capable of working at cryogenic temperatures. Use of the sensor on a spacecraft imposes several reliability and safety constraints, as well as the desire to minimize mass (the sensor mass is 15 g). The impact force profile, measured at 10 kHz by the sensor, allows estimation of the density and cohesion of the surface material, and its particle size distribution. Sample profiles for terrestrial materials (sand, gravel and clay) are given