New nuclear deflection simulations advance planetary defense against asteroid threats

[Jim__]

From phys.org

A modeling tool developed by scientists at Lawrence Livermore National Laboratory shows the progression an asteroid being broken up by a theoretical nuclear device detonated near the the surface of the near-Earth object. Credit: Mary T. Burkey
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Researchers at Lawrence Livermore National Laboratory (LLNL) have developed a modeling tool for assessing the potential use of a nuclear device to defend the planet against catastrophic asteroid impacts.

The research, published today in the Planetary Science Journal, introduces a novel approach to simulating the energy deposition from a nuclear device on an asteroid's surface. This new tool improves our understanding of the nuclear deflection's radiation interactions on the asteroid's surface while opening the door to new research on the shockwave dynamics affecting the inner asteroid.

This model will allow researchers to build upon the insights gained from NASA's recent Double Asteroid Redirection Test (DART) mission, where, in Sept. 2022, a kinetic impactor was deliberately crashed into an asteroid to alter its trajectory. However, with limitations in the mass that can be lifted to space, scientists continue to explore nuclear deflection as a viable alternative to kinetic impact missions.

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"If we have enough warning time, we could potentially launch a nuclear device, sending it millions of miles away to an asteroid that is headed toward Earth," Burkey said. "We would then detonate the device and either deflect the asteroid, keeping it intact but providing a controlled push away from Earth, or we could disrupt the asteroid, breaking it up into small, fast-moving fragments that would also miss the planet."

more ...

The full article is open access and is available here

[keithbvadu2]

1. Bad vacation

[eppur_se_muova]

2. On the surface ?? What for ?? Penetrate far below the surface before exploding and ...

you get a rocket effect, using the asteroid's own substance as propulsive mass.

[Jim__]

3. Kinetic impact is the preferred method, but there are some constraints as to when that will work.

This article is describing models for alternative methods when the constraints make kinetic impact less likely to work. An excerpt from the paper:

In the case of mitigation missions, substantial progress has been achieved in developing options for preventing impacts (Dearborn & Miller 2015), most notably culminating in NASA's Double Asteroid Redirection Test (DART), which executed the first successful deflection of an asteroid in 2022 (Thomas et al. 2023). The DART mission impacted the smaller of a binary asteroid pair to demonstrate a kinetic impact deflection, which, for conditions when it can be effective, is considered the preferred mitigation mission option (National Research Council 2010). However, while the limits of kinetic impactor effectiveness depend upon the individual orbital and geotechnical characteristics of each asteroid (Barbee et al. 2018; Dearborn et al. 2020), the likely applicable size range (∼100–200 m for a rubble-pile asteroid) and warning time constraints (≳10 yr) are restrictive. For example, with a maximum-mass Falcon Heavy payload (4500 kg) intercepting an asteroid at 6 km s−1 (DART velocity), a 170 m diameter spherical asteroid with a bulk density of 2 g cc−1 would have a deflection velocity (Δv) of 1.05 cm s−1. Applying the nominal Earth-miss condition defined in Ahrens & Harris (1992), Δv = 10 cm s−1 per year of warning time, this intercept would need to occur approximately 10 yr or more before the Earth impact date. As described in Dearborn & Miller (2015), kinetic impactor effectiveness is also limited by the maximum velocity that can be delivered to an asteroid without unintentionally weakly disrupting it. This limit, sometimes provided as a percentage of asteroid escape velocity, may depend upon characteristics such as porosity, strength, and rotational state but generally becomes easier to exceed with smaller asteroid sizes. If a kinetic impactor mission design requires the deflection velocity to be either greater than the disruption limit or what can be delivered by available launch capabilities, a longer warning time would be necessary or an alternative mission type should be considered.

Utilizing a nuclear explosive device (NED) to carry out a mitigation mission is a versatile, effective approach to deflecting or disrupting NEOs, including more challenging scenarios. An NED has the highest energy output per unit mass that modern technology can produce. Yield delivered to a potential NEO can be tuned postlaunch by adjusting the height of burst (HOB) between the device and the object's surface. If the mission design requires that the NEO be kept intact and merely given a "push" (a deflection mission), the nuclear device can be detonated at a large HOB compared to the NEO diameter. The radiation from the detonation will propagate freely through the vacuum of space to illuminate a large swath of the object's surface area, causing the material to heat up, vaporize, and expand rapidly. The "blowoff momentum" (pb ) of the newly ejected mass is balanced by an equal momentum in the opposite direction that alters the NEO's total velocity. If the NEO is too small to withstand an attempted deflection mission, or if the warning time requires an impulse so aggressive that it risks fragmenting the object into several potential impactors, the NED can be detonated in close proximity to the object for an intentional disruption mission. In addition to the substantial vaporized ejecta, a successful disruption will cause a shock wave to propagate through the asteroid, breaking it into many small, harmless, fast-moving fragments. Simulations have shown that if such a mission is carried out at least a month before impact, for a 1 Mt device detonated 15 m from a 100 m asteroid, over 90% of the NEO's material will miss the Earth entirely (King et al. 2021). However, if such a mission were attempted via a flyby spacecraft, fast closing speeds (∼10 km s–1) and radar functionality would limit standoff distance precision to the tens of meters range. A slower closing velocity or future radar developments will improve the capabilities of a flyby mission. For a mission design that either requires a precise, small (tens of meters) standoff distance or deploys multiple sequential device detonations from a single spacecraft, a full rendezvous mission will be required. In either case, the detonation is conducted millions of miles from Earth, where the device's radiation does not pose a threat. 2