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Momentum Enhancement Computations For Solid and Fragmented Rocks

Presentation #510.09 in the session Asteroids: Planetary Defense (Oral Presentation)

Published onOct 23, 2023
Momentum Enhancement Computations For Solid and Fragmented Rocks

The ejected material produced during an impact on a target increases the momentum transfer to the target by the momentum of the ejecta. The ratio of the final momentum of the object impacted to the initial momentum of the projectile is called momentum enhancement. The Greek letter beta is sometimes used as the symbol for the ratio. It has been shown in small scale laboratory tests that beta can be very close to 1, when very porous objects are impacted, or as large as 5 when a loosely compacted rubble pile is impacted by a 30 mm sphere at 5 km/s. Recently, the DART mission proved that, when using a spacecraft to impact the asteroid Dimorphos (seemingly a rubble pile of roughly 100 m diameter), the momentum enhancement is likely to be around 3.6.

Computations using the CTH Eulerian code from Sandia National Laboratories and with EPIC, a Lagrangian Elasto-plastic Impact Code maintained by Southwest Research Institute, have shown the following interesting aspects: 1) In general, i.e. across the different projectile scale sizes and impact velocities, the codes cannot properly predict beta, even when sophisticated material models are being used, 2) For some particular problems there were some promising results, for example CTH predicted reasonably well beta for impact of an aluminum sphere on pure iron at 5.5 km/s, 3) CTH did not do well with rock materials, 4) By adding bulking to the failure physics within EPIC, it was possible to obtain good predictions of beta for impact into sandstone targets.

In this presentation the last results of computations using EPIC will be presented and compared to the experiments available. In particular, the main interest was to capture the essence of the physics of an impact on a rubble pile and compare its behavior with the behavior of the impact on a solid slab.

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