CASSE — The ROSETTA Lander Comet Acoustic Surface Sounding Experiment — status of some aspects, the technical realisation and laboratory simulations

A method for inverting the touchdown shock of the Philae lander on comet 67P/Churyumov-Gerasimenko

“…The corresponding strains ε in ultrasonic measurements are very small, less than 10 -6 , so that one indeed measures elastic quantities, here E and G (Truell et al, 1969) and not a plastic quantity, see also the discussions above. Finally, note that the velocities in the sands are higher than in comet analog material (Kochan et al, 2000). …”

“…The detailed analysis of the contact resonances of the soles by finite-element techniques should allow to obtain more quantitative data on the elastic and plastic properties of the landing site in conjunction with the time-of-flight data of the sounding signals on the comet surface generated by the CASSE instrument (Kochan et al, 2000;Seidensticker et al, 2007).…”

“…The diameters of the transducers were 40 mm and hence the weight amounted to a static pressure of ≈ 80 kPa with which the sands were loaded. From the sound velocities and the densities, it is straightforward to calculate Young's modulus E, the shear modulus G, and the Poisson ratio for both aggregates, using well-known equations (Truell et al, 1969) and which are also the basis for the CASSE experiment (Kochan et al, 2000;Seidensticker et al, 2007). We obtain for WF 34 E = 241 MPa, G = 108 MPa and υ = 0.12 and for MSS-D E = 469 MPa, G = 175 MPa, and υ = 0.34.…”

“…The derived analytical expressions allow a rapid estimate of the comet surface elastic and plastic properties. A detailed modeling of the comet soil mechanical properties may follow together with sound velocity data obtained by the Comet Acoustic Surface Sounding Experiment (CASSE) (Kochan et al, 2000;Seidensticker et al, 2007) and data from the Philae thermal and mechanical properties probe MUPUS (Spohn et al, 2009) …”

Sesame – An Experiment of the Rosetta Lander Philae: Objectives and General Design

“…These laboratory studies of regolithic dust and sand as well as frozen ice/dust mixtures showed that acoustic sounding can be applied to cometary surfaces as well (Kochan et al, 2000;Kretschmer, 2000). Figure 3 presents sound transfer data measured with an ice-mineral sample.…”