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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.

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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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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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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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Options

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Deliberate, robust disruption is an option for smaller

objects and/or short warning times

Disruption


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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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


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