Science / Technology - Colloquium
Friday, November 2, 2007
3:00 PM-4:00 PM
Olin Hall
118
Comets are thought to contain pristine material from the time of the formation of the planets.
The Comet Acoustic Surface Sounding Experiment
(CASSE) is an instrument of the Surface Electric Sounding and Acoustic Monitoring Experiment
(SESAME) within the Rosetta mission built in international European co-operation. The Rosetta mission spacecraft was launched in April 2004.
The spacecraft itself carries a number of experiments and also a lander called Philae which will land on comet 67P/Churyumov-Gerasimenko in 2014. The main goals of SESAME are to measure mechanical and electrical properties of the cometary surface and the shallow subsurface as well as of the particles emitted from the cometary surface. Most of the sensors are mounted within the six soles of the landing gear feet, in order to provide good contact with or proximity to the cometary surface.
CASSE is designed to obtain data on the elastic properties of the comet surface by measuring the time-of-flight of surface P- and S-wave signals around 1 kHz. The sounding experiments to be performed are also used to obtain information on the structure of the comet material by means of backscattering. The sounding signals are generated by piezo-composites mounted in the lander-soles. The piezo-composites were built by the IZFP.
This contribution discusses the concept and the scientific and engineering aspects of the CASSE experiment. In particular the construction of the transducers and the expected scenario of wave propagation on a comet surface will be discussed, as well as the inversion of the data in order to obtain the wanted quantities, in particular elasticity and porosity. Some of the concepts for the inversion of the data are lent from NDE of porous materials. In highly attenuating fine-grained sand the obtainable signal-to-noise ratio of piezo-composites of the CASSE instrument was evaluated. Data which were used in the design of CASSE were also obtained by measurement of sound attenuation and sound velocity in comet-analog material which is a watery suspension of minerals, mostly olivine injected via spray guns into a dewar vessel, filled with liquid nitrogen (LN2) and producing a fluffy ice/mineral mixture.
Cost: FREE
Sponsored by: WPI Physics Department, Dr. Stephen Jasperson
Suggested Audiences: College
E-mail:
sak@wpi.edu
Phone: 508-831-5322
Last Modified: October 24, 2007 at 3:07 PM
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