Characterization of space dust using acoustic impact detection.

This paper describes studies leading to the development of an acoustic instrument for measuring properties of micrometeoroids and other dust particles in space. The instrument uses a pair of easily penetrated membranes separated by a known distance. Sensors located on these films detect the transient acoustic signals produced by particle impacts. The arrival times of these signals at the sensor locations are used in a simple multilateration calculation to measure the impact coordinates on each film. Particle direction and speed are found using these impact coordinates and the known membrane separations. This ability to determine particle speed, direction, and time of impact provides the information needed to assign the particle's orbit and identify its likely origin. In many cases additional particle properties can be estimated from the signal amplitudes, including approximate diameter and (for small particles) some indication of composition/morphology. Two versions of this instrument were evaluated in this study. Fiber optic displacement sensors are found advantageous when very thin membranes can be maintained in tension (solar sails, lunar surface). Piezoelectric strain sensors are preferred for thicker films without tension (long duration free flyers). The latter was selected for an upcoming installation on the International Space Station.