Part 2 of 2 parts (Please read Part 1 first)
     Lansing Horan IV is the leader of the research team. He said that there were two basic options in defeating an incoming asteroid. These two options are disruption or deflection.
      Disruption is the procedure of hitting the asteroid with so much energy that it is shattered into many fragments moving at high velocities. He said, “Past work found that more than 99.5 percent of the original asteroid’s mass would miss the Earth. This disruption path would likely be considered if the warning time before an asteroid impact is short and/or the asteroid is relatively small.”
      Deflection is a gentler approach to dealing with asteroids. It consists of imparting a smaller amount of energy to an incoming asteroid which keeps the object intact and pushes it into a slightly different orbit with a small change in velocity. Horan said, “Over time, with many years prior to impact, even a miniscule velocity change could add up to an Earth-missing distance. Deflection might generally be preferred as the safer and more ‘elegant’ option, if we have sufficient warning time to enact this sort of response. This is why our work focused on deflection.”
     This research project was carried out in two primary phases that included neutron energy deposition and asteroid deflective response.
      For the energy deposition phase of the project, the Los Alamos National Laboratory’s Monte Carlo N-Particle (MCNP) radiation-transport program was used to simulate all the different case studies that were compared as part of this research. The MCNP simulated a standoff detonation of neutrons that radiated toward a spherical silicon oxide asteroid one thousand feet in diameter. The asteroid was divided by hundreds of concentric or nested spheres as well as encapsulated cones to form hundreds of thousands of cells. Energy deposition was calculated and tracked for each individual cell. This was done in order to generate the energy deposition profiles or spatial distributions of energy throughout the asteroid.
     For the asteroid deflection phase of the program, the LLNL’s 2D and 3D Arbitrary Lagrangian-Eulerian (ALE3D) hydrodynamics program was used to simulate the asteroid material’s response to the considered energy depositions. The MCNP-generated energy deposition profiles were imported and mapped into the ALE3D asteroid in order to initialize the simulations. The resulting deflection velocity change was obtained for various configuration of neutron yields and neutron energies. This allowed for the quantification of the effect of the neutron energy on the resulting deflection.
     Horan said that the work of his team is one small step forward in the study of nuclear deflection simulations. He added that “One ultimate goal would be to determine the optimal neutron energy spectrum, the spread of neutron energy outputs that deposit their energies in the most ideal way to maximize the resulting velocity change or deflection. This paper reveals that the specific neutron energy output can impact the asteroid deflection performance, and why this occurs, serving as a stepping stone toward the larger goal.”
     Horan pointed out that the research showed that precision and accuracy of the energy deposition data was very important. He said, “If the energy deposition input is incorrect, we should not have much confidence in the asteroid deflection output. We now know that the energy deposition profile is most important for large yields that would be used to deflect large asteroids.”
     Horan went on to say that if there were to be a plan to mitigate a large incoming asteroid, the energy deposition spatial profile should be accounted for in order to correctly model the expected impact of the nuclear detonation on the change in velocity for the asteroid. He said, “On the other hand, the energy coupling efficiency is always important to consider, even for low yields against small asteroids. We found that the energy deposition magnitude is the factor that most strongly predicts the overall asteroid deflection, influencing the final velocity change more than the spatial distribution does.”
     In order to plan an asteroid mitigation mission, it will be necessary to account for these energy parameters to have correct simulations and expectations. Horan said, “It is important that we further research and understand all asteroid mitigation technologies in order to maximize the tools in our toolkit.  In certain scenarios, using a nuclear device to deflect an asteroid would come with several advantages over non-nuclear alternatives. In fact, if the warning time is short and/or the incident asteroid is large, a nuclear explosive might be our only practical option for deflection and/or disruption.”