Abstract
In the future, a hazardous asteroid will find itself on a collision course with Earth. 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 the output neutron energy from a nuclear device standoff detonation affects the deflection of a notional asteroid that is 300 meters in diameter and composed of silicon dioxide at a bulk density of 1.855 g/cm3. 14.1 MeV and 1 MeV neutron energy sources were modeled in MCNP to quantify the energy deposition in the asteroid target. The asteroid’s irradiated region was discretized in angle by tracing the rays emanating from the point of detonation and in depth by considering the neutron mean-free-paths. This high-fidelity approach was shown to deviate from previous analytic approximations commonly used for asteroid energy deposition. 50 kt and 1 Mt neutron yields of the energy deposition mappings were imported into a hydrodynamic asteroid model in ALE3D to simulate the deflective response due to blow-off ejecta. Underexplored in literature, changing the neutron energy was found to have up to a 70% impact on deflection performance due to induced differences in the energy deposition profile and in the energy coupling efficiency. The magnitude of energy deposition accounted for most of the observed variation in the asteroid velocity change, making the coupling efficiency more significant than the spatial profile characteristics. These findings are vital for determining the optimal source neutron energy spectrum for asteroid deflection applications.
Highlights
Background and introductionAsteroid collisions with Earth can be entirely unnoticed or apocalyptic, and everywhere in-between
This paper is divided into the major sections that follow: Section 3 defines the standoff distance and details the spatial discretization procedure, Section 4 states the Monte Carlo N-Particle (MCNP) setup, Section 5 provides the results and analysis of the MCNP energy deposition simulations, Section 6 states the ALE3D setup, Section 7 provides the results and analysis of the ALE3D asteroid deflection simulations, and Section 8 summarizes the overall findings from these efforts
A 300 m SiO2 asteroid was modeled in MCNP, and the neutron energy deposition was calculated from a nuclear device detonation at a standoff distance of ∼62.13 m
Summary
Asteroid collisions with Earth can be entirely unnoticed or apocalyptic, and everywhere in-between. A single asteroid of this size – where the family of 140+ m NEAs collectively has about a 1% chance of one member hitting Earth per 100-year period [7] – would release approximately 100+ megatons (Mt) of TNT-equivalent to Earth, presenting a severedamage risk at the regional level This devastating amount of energy from such an asteroid collision would well surpass the 50 Mt yield of the ‘‘Tsar Bomba’’ Soviet nuclear device, which remains the largest nuclear explosion in history [8]. Neutrons are the only form of radiation output considered from a nuclear detonation, because neutrons are generally the most penetrative and the most effective source type for deflection [14] This is not intended to suggest that extant nuclear devices which principally produce x-rays are somehow unproductive against asteroids. This paper is a step towards determining both the optimal device for asteroid defeat and the type of simulation methodology that can evaluate nuclear deflection performance
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