Options and uncertainties in planetary defense: Impulse-dependent response and the physical properties of asteroids

• Published in: Acta astronautica Vol. 166; pp. 290 - 305
• Main Authors: Dearborn, David S.P., Bruck Syal, Megan, Barbee, Brent W., Gisler, Galen, Greenaugh, Kevin, Howley, Kirsten M., Leung, Ronald, Lyzhoft, Joshua, Miller, Paul L., Nuth, Joseph A., Plesko, Catherine S., Seery, Bernard D., Wasem, Joseph V., Weaver, Robert P., Zebenay, Melak
• Format: Journal Article
• Language: English
• Published: Elmsford Elsevier Ltd 01.01.2020; Elsevier BV
• Subjects: Aeronautics; Asteroid collisions; Asteroid deflection; Asteroid impact; Asteroids; Bennu; Blackbody; Ejecta; Impact velocity; Impactors; Kinetic impactor; Material properties; Near-Earth Objects; NEO mitigation; Nuclear deflection; Physical properties; Planetary defense; Porosity; Security; Technology; Uncertainty; X ray sources; Kinetic impactor; Nuclear deflection; Asteroid deflection; Bennu; NEO mitigation; Planetary defense
• ISSN: 0094-5765; 1879-2030
• DOI: 10.1016/j.actaastro.2019.10.026

Though rare, asteroid impacts are inevitable, and with the current state of technology, kinetic impactors are the preferred but not the complete solution. If the time to impact is short, or the threatening body too large, nuclear deflection serves as a final option. This work is part of an integrated study by National Aeronautics and Space Administration (NASA) and the National Nuclear Security Administration (NNSA) to better determine the relative efficacy of these complimentary approaches. In particular, we examine the important material properties that affect each approach, to improve critical characterization efforts, and reduce uncertainty in the limits of the impactor technology. Impact speeds for kinetic impactors on Near-Earth Object (NEO) intercept trajectories commonly range from 5 to 20 km/s, resulting in significant crater ejecta and a momentum enhancement above that carried by the impactor. This enhancement depends substantially on the strength and porosity of the asteroid, as well as the impact speed. Here simulations from different codes are presented, along with constraints from experimental measurements. The uncertainties due to ignorance of the strength and porosity of the impact point are significant in determining the limits of impactor sufficiency. The nuclear approach is considered within the context of current capabilities, posing no need to test, as extant and well-understood devices are sufficient for the largest known Potentially Hazardous Objects (PHOs). Results of x-ray sources with realistic spectra as well as blackbody spectra are given, along with some assessment on composition dependence. •Asteroid Bennu can be successfully deflected by extant nuclear devices.•Kinetic impact, even with large momentum enhancement, is unlikely to deflect Bennu.•Nuclear deflection efficacy depends upon the x-ray source spectrum.•Nuclear deflection efficacy is enhanced by near-surface, unbound volatiles.•Code comparisons for kinetic and nuclear deflection simulations show good agreement.