Using nuclear devices to deflect or destroy an asteroid. Sounds a little crazy, no? Maybe a little too Hollywood? Yet one day it may be necessary to detonate nuclear weapons in space to defend the planets. For this method to be effective, scientists must work out all the details in advance. That means knowing how much force is required depending on the mass and trajectory of the asteroid.
Recently, a research collaboration between the Lawrence Livermore National Laboratory (LLNL) and the Air Force Institute of Technology (AFIT) examined how the energy output of a nuclear detonation could affect the path of an asteroid. This consisted of modeling various nuclear reactions (fission or fusion) to determine the neutron energy produced, which could potentially pave the way for a new type of asteroid diversion mission (ARM).
Her research is described in a study entitled “Influence of Neutron Energy on Asteroid Distraction Efficiency,” recently published in the journal Acta Astronautica. The team behind it was led by Lansing Horan IV and colleagues from the Air Force Institute of Technology (AFIT), who conducted the research as part of a collaboration with the Main Directorate for Arms and Complex Integration at the LLNL.
Artist’s concept of a large asteroid passing the Earth-Moon system. Photo credit: A combination of ESO / NASA images courtesy of Jason Major / Lights in the Dark.
For their study, the team focused on neutron radiation, which is produced by two different types of nuclear detonation – fission (an atomic bomb) and fusion (a thermonuclear bomb). This was because neutrons can be more penetrating than X-rays, another form of radiation produced by a nuclear detonation. In addition, neutrons of different energies can interact with the same matter through different mechanisms.
Deflection vs. Disturbance
By directly comparing these two types of nuclear reactions, the team was able to get a better idea of which types of neutron energies would be better for planetary defense. Basically there are two ways to defeat an asteroid: disruption or distraction. As Horan recently explained in a press release from LLNL, one disruption is giving an asteroid so much energy that it breaks into many fragments:
“This means that a neutron harvest can potentially heat larger amounts of asteroid surface material and therefore be more effective at deflecting asteroids than an X-ray harvest.”
“Previous work indicated that more than 99.5 percent of the mass of the original asteroid would miss Earth. This fault path would likely be considered if the warning time before an asteroid impact is short and / or the asteroid is relatively small. “
In contrast, distraction is a gentler approach, giving the asteroid a smaller amount of energy to keep it off course – otherwise it remains intact. Similarly, core devices are designed to produce varying energy yields, with fission explosions being measured in kilotons (kt) and fusion explosions being measured in megatons (Mt).
With the right timing and calculations, even a small amount of energy could distract an asteroid well in advance. As Horan summarized:
“Over time, many years before impact, even a tiny change in speed could add up to a distance with no earth. The distraction may generally be preferred as a safer and more elegant option if we have enough warning time to perform this type of response. So our work focused on the distraction. “
Execute numbers
To find out which option was best, the team divided their research into two main phases, including the deposition of neutron energy and the diversionary response of asteroids. The first phase was carried out using the Monte Carlo N-Particle Radiative Transport Code (MCNP) developed by the Los Alamos National Laboratory to track how different particles behave over a wide range of energies.
Using MCNP, the team looked at a series of energy deposition scenarios involving a spherical asteroid 300 meters in diameter and composed of silicon oxide (SiO2). This asteroid has been divided into hundreds of concentric spheres and cones to create hundreds of thousands of cells. They then considered how radiating neutrons would deposit energy on this asteroid and how it would be distributed inside.
The second phase, based on the LLNL’s 3D Arbitrary Lagrangian-Eulerian (ALE3D) hydrodynamic code, was to simulate how the asteroid’s material would react to the various energy depositions under consideration. The MCNP profiles were then imported and integrated into the ALE3D asteroid, and the simulations were run.
The primary research phase relied on MCNP to determine the spatial distribution of a strong neutron blast on an asteroid. Photo credit: LLNL
They found that different energy deposition profiles resulted in drastically different changes in the direction and speed of an asteroid, suggesting that this is the main factor (and not the spatial distribution). They also concluded that deflection is preferable to jamming and that precision and accuracy are paramount, especially when it comes to large yields used to deflect large asteroids.
As Horan has indicated, while there is still much research to be done in their work, it is a step towards nuclear distraction simulations. When the time comes to plan an asteroid mitigation mission, the ability to take into account these energy parameters is critical to success:
“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 have several advantages over non-nuclear alternatives. If the warning time is short and / or the incident asteroid is long, a nuclear explosive may be our only practical option for diversion and / or disruption. “
This joint research was carried out as part of the Horan master’s degree in nuclear technology at AFIT. He was joined by Darren E. Holland and James E. Bevins, Research Associate and Assistant Professor of Nuclear Technology at AFIT. Her co-authors included Megan Bruck Syal and Joseph Wasem from the General Direction of Arms and Complex Integration at LLNL.
Further reading: LLNL, Acta Astronautica
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