Speaker
Description
Several techniques may be appropriate for deflecting a threatening asteroid on a collision course with Earth. Slow-push techniques, such as gravity tractors, require long lead times. Fast-push techniques such as nuclear standoff bursts require much less lead time but come with a host of additional issues. Kinetic impactors are an alternative fast-push technique that can be used on small-to-medium hazards with moderate warning time. The Double Asteroid Redirection Test (DART) mission showed the efficacy of the kinetic impactor technique when it successfully changed the orbital period of Dimorphos in 2022. Despite the success of the DART mission, questions still remain about the efficiency of momentum transfer with this technique. Modeling work performed in support of DART suggests that properties such as material strength, porosity, crush properties, asteroid internal structure, and inherent flaw distribution, can significantly affect the deflection that will be caused by a kinetic impactor. Here, we undertake a set of experiments to better constrain how material strength and target structure affect the outcomes of kinetic impactor asteroid deflection.
We constructed “designer asteroids” with varying internal structures, from coherent asteroids to rubble piles, and performed impact experiments at the Johns Hopkins Applied Physics Laboratory (APL) Impact Lab and the NASA Ames Vertical Gun Range (AVGR) to evaluate the momentum transfer efficiency following impact. Impact velocities ranged from 0.15-0.35 km/s at the APL impact lab, to 1-2 km/s at the AVGR. Spherical targets were created using a range of well understood plaster materials of varying strengths. Rubble piles were created using plaster matrix material surrounding either aquarium gravel or porous pumice. All these plasters have well characterized strength properties ranging from 10 to 117 MPa. The internal structure of the targets were evaluated using x-ray CT scans, the shape and volume of the craters and resulting deformation was tracked, and a ballistic pendulum was used to track deflection.
High-speed videos were used to measure the impact location and angle and to determine the displacement and rotation of the target following impact. We used particle and object tracking algorithms to compute the horizontal, vertical and lateral displacements, and the rotations of the pendulum to determine post-impact momentum. We also measure the ejection speed and direction of target ejecta, to understand the origin of any momentum enhancement, and characterize the shape and mass of the largest individual ejecta.
Differences in momentum enhancement are seen across velocity and target structures. We find that more porous targets do not generate significant ejecta and likely cause less momentum change, which is consistent with findings in the literature. We also note that impact angle significantly alters the linear momentum transferred. Strength differences in less porous target show greater momentum changes relative to the mounting plaster, but show subtle changes when compared to each other with stronger targets possible showing less efficient momentum enhancement. Rubble pile targets behave noticeably differently than homogenous targets. In this presentation, we will describe the initial experiments, results, and discuss internal structure effects on deflection.