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

Faber, Claudia; Knapmeyer, Martin; Roll, R.; Chares, B.; Schröder, Silvio; Witte, Lars; Seidensticker, K. J.; Fischer, Hans-Herbert; Möhlmann, D.; Arnold, W.

doi:10.1016/j.pss.2014.11.023

Cited by 8 publications

(4 citation statements)

References 24 publications

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“…Because the mechanical response of Philae (damping element, structural elasticity, rotation, and flywheel) is complicated and superimposed on the surface strength decelerations upon touchdown, we combined a soil mechanics force model (3,11) with a numerical multibody simulation of Philae (10) that was calibrated and verified with test data from a Philae mockup (10,22). The goal is to determine the soil properties, including strength, elastic constants, dissipation, excavation mechanics, possible layering, and horizontal inhomogeneity (e.g., boulder versus finer regolith).…”

Section: Discussionmentioning

confidence: 99%

“…The postulated competent layer below has an unknown thickness, with an unknown compressive strength. Only its elastic parameters can be estimated from the CASSE signals using Hertz's contact theory and the sole's resonances (22). Yet this layer appears to be strong and/or thick enough to withstand the dynamical loads exerted by Philae's feet, because breakage of that layer and transition to the presumably soft granular material beneath is not seen in the data.…”

Section: Discussionmentioning

confidence: 99%

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The landing(s) of Philae and inferences about comet surface mechanical properties

Biele

Ulamec

Maibaum

et al. 2015

Science

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233

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The Philae lander, part of the Rosetta mission to investigate comet 67P/Churyumov-Gerasimenko, was delivered to the cometary surface in November 2014. Here we report the precise circumstances of the multiple landings of Philae, including the bouncing trajectory and rebound parameters, based on engineering data in conjunction with operational instrument data. These data also provide information on the mechanical properties (strength and layering) of the comet surface. The first touchdown site, Agilkia, appears to have a granular soft surface (with a compressive strength of 1 kilopascal) at least ~20 cm thick, possibly on top of a more rigid layer. The final landing site, Abydos, has a hard surface.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

The landing(s) of Philae and inferences about comet surface mechanical properties

Biele

Ulamec

Maibaum

et al. 2015

Science

Self Cite

233

142

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“…Furthermore, the forced resonances of the foot-soles could be used to obtain information on the local elastic modulus E. These principles and mode of operation have been discussed in an earlier paper describing the landing tests at the DLR Landing & Mobility Test Facility (LAMA Tests). 6) The operation mode "contact-resonances" resembles the well-known Fokker-Bond test in non-destructive materials characterization to check the integrity of bonds in the aeronautic industry. 7,8) The signals obtained at the first landing site Agilkia appeared in distinct groups, see Figs.…”

Section: Cassementioning

confidence: 99%

Surface mechanical properties of comet 67P

Arnold

Fischer²,

Knapmeyer

et al. 2019

Jpn. J. Appl. Phys.

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“…We also discuss the effect that is generated by the compressive deformation of the sole of the landing gear. The elastic modulus of thesole is made of compound glass fibre an approximately equals 21.1 GPa (Faber et al 2015;Möhlmann et al 2018), which is much larger than that of the equivalent surface of Agilkia, which is about 10 MPa (Möhlmann et al 2018). The deformation of the base of the landing gear can therefore be neglected.…”

Section: Mechanical Dynamics Of the Landermentioning

confidence: 99%

Characterization of the Agilkia region through discrete-element simulation of Philae’s rebound

Küppers

Grieger

et al. 2019

A&A

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Context. The cold gas system and anchoring harpoons that were designed to hold Philae down after it landed on the Agilkia region of comet 67P/Churyumov-Gerasimenko (67P) failed. This caused the lander to move on a complex trajectory that comprised multiple impacts and rebounds. The motion of Philae was mainly dominated by the gravitational environment and the physical properties of the surface on Agilkia. This allows us to determine the physical properties of the surface layer by high-fidelity discrete-element simulations of Philae’s rebounds. Aims. We explore the surface physical properties of the Agilkia region on comet 67P by minimizing the difference in Philae’s rebound status between observational data and simulations based on the assumption of a granular-boulder hybrid surface material. Methods. We first developed an efficient gravity model to accurately approximate the high-resolution polyhedral shape of the comet. This allowed us to run many simulations for the landing trajectory. We developed a complete dynamical model of the motion of Philae, including a mechanical model of the lander and the hybrid surface model. This focused in particular on the interaction of discrete elements in Philae and the granular regolith layer with a boulder added on top of it. We used mixed discrete optimization to determine the input physical variables on Agilkia to fit the rebound observational data (Philae’s rebound velocity). Results. The discrete-element simulation constrained by Philae’s rebound velocity implies that Philae first impacted on a boulder and scratched it with the landing gear. After this, its three soles interacted with the granular regolith, which consists of particles with a mean diameter of 0.014 ± 0.004 cm. The thickness of the region interaction is estimated to be 0.272 ± 0.062 m with a corresponding density of 1443 ± 231 kg m−3. The Young modulus for each particle is estimated to be 108 Pa. Based on a porosity of 0.75, the friction of the surface of particles is derived to be moderate, with a friction coefficient of about 0.6.

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

Cited by 8 publications

References 24 publications

The landing(s) of Philae and inferences about comet surface mechanical properties

The landing(s) of Philae and inferences about comet surface mechanical properties

Surface mechanical properties of comet 67P

Characterization of the Agilkia region through discrete-element simulation of Philae’s rebound

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