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Los Alamos National Laboratory, Los Alamos, NM 87545, USA
Received: December 21, 2011 / Accepted: January 10, 2012 / Published: February 15, 2012.
Abstract: This paper shows 2D and 3D simulations from a validated hydrocode (RAGE) of the effects of a strong explosion on the surface of a porous non-spherical asteroid like object. The composition of the simulated asteroid is made more realistic than previous work by using a random distribution of rocks constrained by a non-spherical outer surface. These simulations can be categorized as explosion effects on “rubble pile” asteroids. The main goal of this work is to apply realistic hydrodynamics to 2D and 3D rubble pile models and examine the results to see if sufficient momentum is transferred to the porous object so as to mitigate the hazard posed by the initially Earth crossing orbit.
Key words: Asteroid mitigation, nuclear explosions, potentially hazardous objects (PHOs).
The authors have performed detailed hydrodynamic simulations of the shock interaction from a strong surface or subsurface explosion with sample asteroid objects. The purpose of these simulations is to apply modern hydrodynamic codes that have been well verified and validated (V&V) to the problem of mitigating the hazard from a potentially hazardous object (PHO), an asteroid or comet that is on an Earth crossing orbit [1]. The cod used for these simulations is the RAGE code from Los Alamos National Laboratory[2-6]. Ref. [2] contains many of the V&V reports for the code which were completed prior to publication. It should be noted for those not familiar with the RAGE code that it has been extensively V&V’d for shock physics and shock interactions with multiple materials. It is confident that the shock physics simulations presented here represent realistic hydrodynamics of the complex shock interactions, including the effect of the shock on the rocks themselves (assumed to be spherically shaped objects).
Initial runs were performed using a spherical object. We next ran simulations using the shape form from a known asteroid: 25143 Itokawa [7, 8]. This particular asteroid is not a PHO but we use its shape to consider the consequences of non-spherical objects. The initial work was performed using 2D cylindrically symmetric simulations and simple geometries (solid non-spherical objects). Next we progressed to Itokawa shaped models filled with uniform size “rocks”composed of granite and a solid background material(alluvium). These models had no porosity and were mainly done as a test of the code hydrodynamics. The first runs used a spherical energy source at the center of the object (typically 1 Mt), both with and without a“drill hole” which would be necessary to emplace an explosive at this location. Since the escape velocity of this object is very low, the disruption and bulk velocities indicated from these simulations is
simple to more complex. The models shown in this paper are:
(1) A non-spherical asteroid 25143 Itokawa shape with a uniform iron composition and a central explosion site. This model was done first to test the code for reasonable results and assess the effects of non-spherical models;
(2) Next we wrote a simple program to fill the non-spherical outer shape of the asteroid with a random distribution of rocks. These rocks could be of arbitrary size between size 1 and size 2 and were spherical in shape with the centroids within the asteroid surface. These models represent what we call“rubble pile” compositions, which is considered to be more realistic on average than uniform or spherical compositions;
(3) The first runs of this type were done with single size “rocks” (really torus’s in 2D) composed of granite material equation-of-state (EOS) with an alluvium background material. Thus these first runs had no porosity. It is generally believed that typical asteroids have porosities of 30%-40% due to multiple collisions and subsequent re-aggregation;
(4) Next we simulated porosity by removing the background alluvium and leaving the granite rocks. This resulted in porosities of 25%-40% (in 3D). The main effect of the high porosity is to significantly degrade the shock strength and therefore impart less momentum to the asteroid;
(5) We then modeled the effect of the depth-of-burial of the explosion from the center of the object to the surface and also the effect of short-side versus long-side surface bursts;
(6) Our final model in this series is running now and is a full 3D porous object filled with three different size rocks from 5 m to 50 m.
4. 2D Results
Work done previously to this meeting included the non-spherical uniform composition central explosion simulation with an energy of 1 Mt. The resulting
images from the 2D RAGE simulation are shown in Fig. 1. This initial model indicated the importance of non-spherical geometry. The shock from the central explosion clearly reaches the surface of the asteroid along the shortest chord and ultimately ejects the two large end caps at a velocity of ~ 50 m/s due to the enormous pressure inside the explosion cavity at breakout time.
Next we used a program to fill the shape object with a distribution of rocks. This first simulation was done with a background material of alluvium and rocks composed of granite with SG strength. Thus this run had no porosity. Again dispersion velocities of all the asteroid material and “rocks” were calculated to be~1 m/s, significantly above the escape velocity. These results are shown in Fig. 2.
Next we explored the asteroid mitigation for various depths-of-burial of the explosion from the center to the surface. These results are shown in Fig. 3.
In summary the effect of the porosity as modeled in 2D here with the RAGE code indicate that even for at 500 kt explosion (modest energy) and significant porosity (~20%) the asteroid material was given a bulk velocity of ~>5 m/s at 10 seconds, sufficient to mitigate the PHO hazard. Thus for short notice PHO’s one should not consider the nuclear explosive option as “off the table”. There are clearly significant international issues to be resolved:
? which nuclear country will be given the lead on such a mission?
? which international organization will be in charge of such a mission?
? should multiple missions be undertaken (at the same time) to ensure mitigation?
The answers to these questions should be addressed in an international forum best suited for the salvation of the Earth. The authors do not make light of the fact that these issues are outstanding and of major concern.
Received: December 21, 2011 / Accepted: January 10, 2012 / Published: February 15, 2012.
Abstract: This paper shows 2D and 3D simulations from a validated hydrocode (RAGE) of the effects of a strong explosion on the surface of a porous non-spherical asteroid like object. The composition of the simulated asteroid is made more realistic than previous work by using a random distribution of rocks constrained by a non-spherical outer surface. These simulations can be categorized as explosion effects on “rubble pile” asteroids. The main goal of this work is to apply realistic hydrodynamics to 2D and 3D rubble pile models and examine the results to see if sufficient momentum is transferred to the porous object so as to mitigate the hazard posed by the initially Earth crossing orbit.
Key words: Asteroid mitigation, nuclear explosions, potentially hazardous objects (PHOs).
The authors have performed detailed hydrodynamic simulations of the shock interaction from a strong surface or subsurface explosion with sample asteroid objects. The purpose of these simulations is to apply modern hydrodynamic codes that have been well verified and validated (V&V) to the problem of mitigating the hazard from a potentially hazardous object (PHO), an asteroid or comet that is on an Earth crossing orbit [1]. The cod used for these simulations is the RAGE code from Los Alamos National Laboratory[2-6]. Ref. [2] contains many of the V&V reports for the code which were completed prior to publication. It should be noted for those not familiar with the RAGE code that it has been extensively V&V’d for shock physics and shock interactions with multiple materials. It is confident that the shock physics simulations presented here represent realistic hydrodynamics of the complex shock interactions, including the effect of the shock on the rocks themselves (assumed to be spherically shaped objects).
Initial runs were performed using a spherical object. We next ran simulations using the shape form from a known asteroid: 25143 Itokawa [7, 8]. This particular asteroid is not a PHO but we use its shape to consider the consequences of non-spherical objects. The initial work was performed using 2D cylindrically symmetric simulations and simple geometries (solid non-spherical objects). Next we progressed to Itokawa shaped models filled with uniform size “rocks”composed of granite and a solid background material(alluvium). These models had no porosity and were mainly done as a test of the code hydrodynamics. The first runs used a spherical energy source at the center of the object (typically 1 Mt), both with and without a“drill hole” which would be necessary to emplace an explosive at this location. Since the escape velocity of this object is very low, the disruption and bulk velocities indicated from these simulations is
simple to more complex. The models shown in this paper are:
(1) A non-spherical asteroid 25143 Itokawa shape with a uniform iron composition and a central explosion site. This model was done first to test the code for reasonable results and assess the effects of non-spherical models;
(2) Next we wrote a simple program to fill the non-spherical outer shape of the asteroid with a random distribution of rocks. These rocks could be of arbitrary size between size 1 and size 2 and were spherical in shape with the centroids within the asteroid surface. These models represent what we call“rubble pile” compositions, which is considered to be more realistic on average than uniform or spherical compositions;
(3) The first runs of this type were done with single size “rocks” (really torus’s in 2D) composed of granite material equation-of-state (EOS) with an alluvium background material. Thus these first runs had no porosity. It is generally believed that typical asteroids have porosities of 30%-40% due to multiple collisions and subsequent re-aggregation;
(4) Next we simulated porosity by removing the background alluvium and leaving the granite rocks. This resulted in porosities of 25%-40% (in 3D). The main effect of the high porosity is to significantly degrade the shock strength and therefore impart less momentum to the asteroid;
(5) We then modeled the effect of the depth-of-burial of the explosion from the center of the object to the surface and also the effect of short-side versus long-side surface bursts;
(6) Our final model in this series is running now and is a full 3D porous object filled with three different size rocks from 5 m to 50 m.
4. 2D Results
Work done previously to this meeting included the non-spherical uniform composition central explosion simulation with an energy of 1 Mt. The resulting
images from the 2D RAGE simulation are shown in Fig. 1. This initial model indicated the importance of non-spherical geometry. The shock from the central explosion clearly reaches the surface of the asteroid along the shortest chord and ultimately ejects the two large end caps at a velocity of ~ 50 m/s due to the enormous pressure inside the explosion cavity at breakout time.
Next we used a program to fill the shape object with a distribution of rocks. This first simulation was done with a background material of alluvium and rocks composed of granite with SG strength. Thus this run had no porosity. Again dispersion velocities of all the asteroid material and “rocks” were calculated to be~1 m/s, significantly above the escape velocity. These results are shown in Fig. 2.
Next we explored the asteroid mitigation for various depths-of-burial of the explosion from the center to the surface. These results are shown in Fig. 3.
In summary the effect of the porosity as modeled in 2D here with the RAGE code indicate that even for at 500 kt explosion (modest energy) and significant porosity (~20%) the asteroid material was given a bulk velocity of ~>5 m/s at 10 seconds, sufficient to mitigate the PHO hazard. Thus for short notice PHO’s one should not consider the nuclear explosive option as “off the table”. There are clearly significant international issues to be resolved:
? which nuclear country will be given the lead on such a mission?
? which international organization will be in charge of such a mission?
? should multiple missions be undertaken (at the same time) to ensure mitigation?
The answers to these questions should be addressed in an international forum best suited for the salvation of the Earth. The authors do not make light of the fact that these issues are outstanding and of major concern.