Date of Award

3-2020

Document Type

Thesis

Degree Name

Master of Science

Department

Department of Engineering Physics

First Advisor

Darren E. Holland, PhD

Abstract

In the future, a hazardous asteroid will find itself on a collision course with Earth. It is an inevitability; the question is not if, but when. For asteroids of moderate size or larger, a nuclear device is one of humanity's only technologies capable of mitigating this threat via deflection on a timescale of less than a decade. This work examined how changing the output neutron energy from a nuclear device detonation affects asteroid deflection. The notional asteroid target was 300 meters in diameter and composed of silicon dioxide at a bulk density of 1.855 g/cm3. To calculate the energy deposition in the asteroid that results from a neutron source, the Monte Carlo radiation-transport code, MCNP6.2, was applied. MCNP6.2 simulations were performed for neutrons of various energies radiating towards the asteroid surface. The neutron energy was found to have an impact in terms of 1) the energy deposition spatial profile, and 2) the energy coupling efficiency. To model the mechanical response of the asteroid due to a spatially-varying energy deposition, the hydrodynamics code, ALE3D, was employed. The energy deposition outputs from MCNP6.2 served as inputs into the model representation of the asteroid in ALE3D. The momentum impulse imparted onto the asteroid body due to rapidly- evolving melted and/or vaporized blow-off ejecta was quantified. From this, the asteroid velocity change, or δV , was determined for two different neutron yields (50 kt and 1 Mt) and for two different source neutron energies (14.1 MeV from fusion and 1 MeV from fission). Underexplored in literature, the distribution of deposited energy and the energy coupling were both found to affect the asteroid deflection. The magnitude of energy deposition, as determined by the neutron energy and the coupling, generally appears to be the more significant factor.

AFIT Designator

AFIT-ENP-MS-20-M-101

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