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LLNL-PRES-673835-DRAFT This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344. Lawrence Livermore National Security, LLC
Lawrence Livermore
National Laboratory
Presented by Paul L. Miller,
with contributions from the NNSA Planetary-Defense Team
1 July 2015
SSGF Conference, Washington, DC
Lawrence Livermore
National Laboratory LLNL-PRES-673835-DRAFT
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Background
• Nature of the threat
• Historical events
• Governmental interest
• Tri-lab activities
Options
• Emergency response
• Deflection
• Disruption
Research drivers
This talk discusses the asteroid impact hazard and our
activities in support of a U.S. Government response
Overview
Asteroid impacts are a national-security threat requiring advanced
science and technology solutions
“Blue Marble” image from NASA.
Lawrence Livermore
National Laboratory LLNL-PRES-673835-DRAFT
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There are thousands of near-Earth asteroids, and more
are discovered every year
Background
Near-Earth Asteroid (NEO)
• Perihelion less than 1.3 AU
— 10,505 known NEOs (Dec. 2013)
— 867 have a diameter > 1km
Potentially-Hazardous Asteroid
(PHA)
• Comes within 0.05 AU of Earth’s orbit;
absolute magnitude ≥ 22
— 1445 known PHAs (Dec. 2013)
Image credit: Paul Chodas, NASA/JPL
Earth’s orbit
NEO discoveries per six-month period Composite of PHA orbits
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15 February 2013: the Chelyabinsk impact highlights the
reality of the risk
Size: ~ 20 m diameter
Yield: ~ 0.5 Mt at 30 km
Approx. 1500 injuries
Background
Images from Wikipedia
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The range of threats are represented by Tunguska (1908) and
the K-T impactor (65 Mya)
Background
K-T
melted/vapor
ized region
Reproduced
with permission
from Stephen Nelson
Near-Earth Object (NEO) Population Estimate
Reproduced with the permission of Alan Harris
Che
lyab
insk
Global Catastrophe Fallen trees,
Tunguska
Image source: Wikipedia
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National Laboratory LLNL-PRES-673835-DRAFT
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There is ongoing attention from the U.S. Government about
the threat of asteroid impacts
1992: U.S. Congress tasks NASA with locating NEOs
larger than 1 km
2007: NASA “Near-Earth Object Survey and Deflection
Analysis of Alternatives” Report to Congress
2008: NASA Authorization Act — NASA lead agency
for NEO detection and deflection mission
2010: OSTP Letter (John Holdren) to Congress
2010: NRC (National Academies) report to Congress,
“Defending Planet Earth: NEO Surveys & Hazard
Mitigation Strategies” identifies nuclear as only option
for larger objects (≥ 1 km)
2013: NASA-FEMA TTX at FEMA HQ
2014: NASA-FEMA TTX2; NASA-DARPA meeting
Background
Image from Wikimedia
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The asteroid-threat problem has many connections to
expertise areas of the NNSA Labs
Nuclear-explosive physics and function
Multi-physics modeling
Ground coupling; underground effects
HPC and 3-D simulations
Algorithm development
Hydrodynamics, EoS, and opacity modeling
Material strength, damage, and failure
V&V and UQ
NNSA capabilities
Asteroid-deflection simulation
Simulation credit: Eric Herbold, Geodyn-L
The topic is a microcosm of the stockpile-stewardship program
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Our primary goal is to support other USG agencies in
understanding mitigation options and impact effects
Objectives include:
Support to other USG agencies
Assessment of U.S. mitigation capabilities
Assessment of impact effects
We are working with NASA:
Interagency Agreement (IAA) is in effect
NASA HQ
• NEO Program Office (JPL)
• Planetary Defense Conference
• FEMA and DARPA interactions
Collaborations with NASA sites
Benefits Objectives
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Planetary-defense activities provide ancillary benefits
The work provides:
Strengthening of related expertise
Community engagement
• University collaborations
• Students and postdocs
• Publications
Recruiting and training
Benefits
Logos copyright of their respective owners.
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Option 1: Take the hit — Emergency Response
Option 2: Deflection (push it off course)
Option 2b: Disruption (break it up and disperse it)
Options
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Water-impact example: Simulation of an impact in the Gulf
of Mexico for a 2014 NASA-FEMA tabletop exercise
Emergency Response
Wave
heights
(meters)
Air
Ocean
Slice: front view
Credit: Souheil Ezzedine and NISAC (SNL)
Codes: Geodyn and Ezzedine
wave-propagation code
Slice: side view
Air
Ocean
50m Fe-Ni
25 deg.
10 Mt
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Option 1: Take the hit — Emergency Response
Option 2: Deflection (push it off course)
Option 2b: Disruption (break it up and disperse it)
Options
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Deflection can be achieved by means of kinetic impactors
(a fast-moving lump of mass)
Deflection
Credit: J. Michael Owen, Spheral ASPH code
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Deflection can be achieved by nuclear explosives
(as an energy-delivery mechanism) — movie
Deflection
Credit: Ilya Lomov, Geodyn code
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Option 1: Take the hit — Emergency Response
Option 2: Deflection (push it off course)
Option 2b: Disruption (break it up and disperse it)
Options
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Deliberate, robust disruption is an option for smaller
objects and/or short warning times
Disruption
Credit: J. Michael Owen, Spheral ASPH code
Strategy:
• Rapid dispersal
• Very large cloud of fragments
• Small pieces (atmosphere
protects against < 10 meters)
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There is a natural trade-off between lead time and the
required v for deflection
Deflection
Graphic credit: David Dearborn
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For shorter lead times the risk of disruption becomes
prominent
Deflection
Graphic credit: David Dearborn
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Research is driven by two major sources of uncertainty:
accuracy of the modeling and the range of initial conditions
Relevant asteroid
parameters include:
Size and shape
Density
Structure
Dynamics
Research drivers
Energy deposition onto
a Bennu shape model.
Simulation credits: J. Michael Owen, Spheral ASPH code; Eric Herbold, Geodyn-L
Itokawa 500m Image credit:
JAXA
Rock or Rubble? !
Protation< 2 hours : Strength Required !
Protation > 2 hours => Maybe Rubble!
!
Solid Evidence accumulating: !MOST bodies <200m have P<2 hr.!
2000 DO8! 0.021 ! 30 !
1998 WB2 ! 0.317 ! 60 !
1999 TY2 ! 0.119 ! 80 !
1995 HM ! 1.62 ! 120 !
2004 VD17 !1.99 !320!
2001 FE90 !0.48 !265-594!
2001 VF2 !1.39 !145-664!
2001 OE84! 0.49 ! 470-820!
!
Object P(hours) Diameter (m) !
Bodies with material strength
exist!!The “spin limit”
Internal structure
Dynamics
Shape effects
Asteroid response is
very scenario
dependent
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Defines warning time and
deflection requirements
Sets the best time, location,
and direction for deflection
Determines future close
passes/keyholes
Defines impact location, angle
of impact, and velocity of
impact
Orbit uncertainty also drives
impact probability, influencing
the decision to take action
An object’s orbit determines if, when, and how an impact
will occur, and the necessity of taking action
#1 Orbit
Impact scenario near San Francisco
Water rims
Air
Ocean
Source generation
impact
Source propagation
California/USA
T=+1hr
Simulations by Souheil Ezzedine
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Interconnected with:
Volume/ surface area/ diameter
Composition
Bulk density
Porosity
Several ways to estimate mass
The uncertainty can be as large as an order of magnitude
Mass also has a strong
influence on disruption limits
Mass (combined with warning time) sets deflection
difficulty, as well as consequences if an impact occurs
#2 Mass
Cartoon used under license
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Equations-of-state for
modeling (including
melting/vaporization points)
— Essential for imparted-Δv
estimates
Nuclear-generated x-ray
deposition
— especially the thin layer at the
surface
Sets density at the grain scale
In particular, the presence of
high-Z (metals) or low-Z
(volatiles) elements plays a
big role
Composition plays a central role in how an asteroid reacts
to a kinetic impactor or nuclear deflection
#3 Composition
Table credit: Kirsten Howley and Rob Managan
X-ray penetration depths into
four materials
Material Density
(g/cm3)
1 keV
depth
(µm)
10 keV
depth
(µm)
Ice 1.0 2.4 1900
Quartz 2.65 1.2 200
Forsterite 3.25 1.1 190
Fe-Ni 7.5 0.14 8
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Strongly influences the
momentum-enhancement (β)
factor for kinetic impactors
— surface porosity often involves
regolith
Strongly influences response
of the object and potential for
disruption
— porosity at depth dampens shock
and limits damage to asteroid
Porosity ranges from
microscopic to macroscopic,
and bulk (average) porosity is
neither
Porosity influences effectiveness of kinetic impactors, as
well as the potential for disruption
#4 Porosity
Regolith compaction for
two different porosities
Simulation credit: Eric Herbold
10% 40% porosity
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Slopes affect direction and
magnitude of Δv from kinetic
impactor
Diminishes/enhances effect
from nuclear compared to a
sphere
— Can be a factor of 2 or more
Rotation further complicates
matters by introducing timing
(see item #7 below)
Shape influences both kinetic and nuclear deflection
effectiveness
#5 Shape
Simulation credit: Megan Bruck Syal
Kinetic impact on
Golevka shape model
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National Laboratory LLNL-PRES-673835-DRAFT
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Interior structure (with composition
and porosity) influences the
potential for disruption
— Rubble pile? Limits of cohesion?
Surface structure influences
— Nuclear-energy deposition
(boulders/roughness)
— Impactor momentum enhancement (β)
Binaries (or even tertiaries)
present complications
Structure is multiscale and
heterogeneous — inherently
difficult to characterize
Beyond shape and porosity, additional aspects of
structure affect the problem
#6 Structure
Simulation credit: Eric Herbold
Aggregate (l) and fractured (r)
objects driven by nuclear-
energy deposition
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Enhances disruption
• cohesive forces may barely hold
object together
• deflection acceleration may
exceed limits
Complicates shape effects
• kinetic: where is impact point?
• nuclear: what face absorbs
energy?
Predicting rotation angle upon
arrival of an interceptor is an
additional complication
Spin further complicates the response of an object and
also introduces timing issues for interceptors
#7 Spin
Simulation credit: Megan Bruck Syal
(not spinning)
(spinning)
radial velocity
plots
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Consider the list of characterization needs discussed —
what methods and platforms are available?
Characteristics
① Orbit
② Mass
③ Composition
④ Porosity
⑤ Shape
⑥ Structure
⑦ Spin
Characteristics
Modeling and simulation efforts can quantify implications of existing
uncertainties and further prioritize data needs
Measurement platforms
Earth-based, space based,
flybys, rendezvous, sample
return, . . .
Measurement methods
Astrometric, visual imaging,
radar, spectral, gravimetric,
sample, . . .
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Asteroid impacts are a national-security threat
requiring advanced science and technology solutions
Asteroid impacts present a range of threats,
including rare but very high-consequence ones
Deflection and/or disruption approaches may be
employed, depending on the situation
The challenge derives from both difficult science
problems and lack of knowledge of initial conditions
A scenario-based approach is needed, because
every case is unique and it is an integrated problem
Summary
The NNSA labs are making contributions on multiple fronts
Credit: J. Michael Owen, Spheral ASPH code