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Momentum Enhancement β in Crushed Basalt Asteroid Surface Analogs with Comparison to DART

Presentation #510.07 in the session Asteroids: Planetary Defense (Oral Presentation)

Published onOct 23, 2023
Momentum Enhancement β in Crushed Basalt Asteroid Surface Analogs with Comparison to DART

For planetary defense through deflection by a hypervelocity impactor, an important measure of efficiency is how much more momentum is transferred to the asteroid due to crater ejecta than is carried by the impacting spacecraft. This momentum enhancement is characterized by the number β, where β > 1 shows the enhancement. Studies of momentum enhancement have shown there is a dependence on the impactor size and density [1,2]. Also, target ductility affects β, where the more brittle the impacted material the larger the momentum enhancement [3,4,5]. Given impactor size dependence, there is also interest in the size distribution of the rocks at the surface of the asteroid comprising a target. Impact experiments from 2 to 5.5 km/s were performed measuring momentum enhancement β. Spherical aluminum impactors were used ranging in diameter from 3 to 4.45 cm.

The surfaces of several small asteroids have been imaged, including Itakawa, Bennu, Ryugu, and now, with DART, Dimorphos. These surfaces show close-packed rocks held in place by gravity and friction. Asteroid analog targets were developed to reflect the surfaces seen at these asteroids.

Impact targets were made from a variety of crushed basalt mixtures, with different size rocks and different amount of a binder. At SwRI a large two-stage light gas gun was used to launch projectiles at high speeds. The targets were hung from a large pendulum whose swing measures the momentum transferred by the impact and ejecta. The momentum enhancement β ranged from 2.8 to 5, depending on the various specifics of rock size and binder. This work shows clear target rock-size-distribution and/or surface rock distribution effect on momentum enhancement. Such a rock-size-distribution effect would presumably also apply to impacts into asteroid surfaces. The measured values in the laboratory are in line with, though with many differences in initial conditions, the preliminary result of the DART impact of β ~ 3.6 [6].

References: [1] Walker, J. D. et al. (2013) IJIE, 56, 12–18. [2] Walker J. D., Chocron S., and Grosch D. J. (2020) IJIE, 135, 103388. [3] Walker J. D. et al. (2023), IJIE, 180. [4] Walker J. D. and Chocron S. (2011), IJIE, 38, A1–A7. [5] Walker J. D. et al. (2022), PSJ, 3. [6] Cheng A. F. et al. (2023) Nature, 616.

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