brent william barbee, m.s.e. emergent space technologies, inc

Systems Engineering Approach to the Mitigation of Hazardous

Near-Earth Objects (NEOs)

Brent William Barbee, M.S.E.Emergent Space Technologies, Inc.

July 11th, 2006

Overview

• Background and Motivation• Systems Engineering Approach• Detection, Characterization, and Mitigation• Mitigation Modes• Deflection Methods• Optimal Impulsive NEO Deflection• Hazardous NEO Scenario Timeline• NEO Mitigation Mission Design Architecture• Conclusions

Background and Motivation

• Near-Earth Objects (NEOs):– Asteroids and comets whose orbits are

in close proximity to Earth’s orbit.• When the phasing is right, such NEOs will

closely approach Earth.• Potentially Hazardous Asteroids (PHAs)

have orbits that come to within 0.05 AU of Earth’s orbit.

– If a NEO’s orbit intersects that of Earth, a collision is possible.

• Depends on phasing (timing).• Annual meteor showers are caused by

Earth passing through the paths of comets.

Photograph of Comet LinearC/2002 T7 [May 2004]

Galileo Photograph of Asteroid Gasprataken October 29st, 1991


• Comets and asteroids:– Comets:

• Have very eccentric, longer orbit periods.• Can be more difficult to detect.• Are much less numerous than Near-Earth

Asteroids (NEAs).• Exhibit jets of volatiles due to heating when in

proximity to the Sun.– Near-Earth Asteroids:

• Orbits are within region of inner planets.• No volatiles.• Very numerous:

– Thousands with mean diameter > 1 km.– Possibly millions with mean diameter of a few

hundreds of meters or less.


• Asteroid orbit classifications:– Earth-crossing:

• Apollos– Semi-major axis > 1.0 AU– Perihelion distance < 1.107 AU

• Atens– Semi-major axis < 1.0 AU– Perihelion distance > 0.983 AU

– Mars-crossing:• Amors

– 1.3 AU > perihelion distance > 1.017 AU


• Asteroid composition classifications:– Wide variety of spectral classifications, but

there are three main types:• S-type

– Silicaceous, majority of inner asteroid belt– Iron mixed with iron- and magnesium-silicates

• M-type– Metallic iron, most of middle asteroid belt

• C-type– Carbonaceous, 75% of known asteroids


• Some nomenclature:– Asteroid:

• Small rocky body orbiting the Sun.– Meteoroid:

• Small particle from a comet or asteroid orbiting the Sun.– Bolide:

• Extraterrestrial body that collides with Earth, or• Exceptionally bright, “fireball” meteor.

– Meteor:• The streak of light created in the sky when an asteroid enters

Earth’s atmosphere.– Meteorite:

• Solid remains of a meteoroid that survives atmospheric passage and lands on Earth’s surface intact.

Photograph of a meteor enteringEarth’s atmosphere.


• NEO internal structure:– Monoliths or rubble piles?

• A rubble pile is a non-cohesive (strengthless) asteroid held together only by gravity.

• Ground observations of spin rates show that most asteroids are not required to be solid.

• However, this is not conclusive evidence that such asteroids are in fact rubble piles.

– Solid asteroids are more susceptible to mitigation techniques that rely on deflection, particularly impulsive deflection.

– Porous asteroids may be more difficult to deflect.


• Collisions with dangerous (large) NEOs are fortunately rare but do happen periodically.

• Small NEOs collide with Earth on a regular basis, however.– Tunguska impact in 1908 destroyed 2000 km2 of

forest in Siberia (and this is a “small” impact).• Devastated an area about the size of Rhode Island.• NEO thought to be ~ 60 m in mean diameter.• This sort of event is expected once per century, on

average.

– Annual meteor showers (e.g., Leonids, Geminids)


– Upper atmosphere bolides (several per year):• It is believed that NEOs that are less than 50 m in mean

diameter will burn up or explode in the upper atmosphere without reaching Earth’s surface.

– Though some may reach lower altitudes before detonation.– Some reach the surface: meteorites.

– There are numerous historical examples extending up to present day.

• 1998: A small meteorite hit the ground 1 meter from a man playing golf.

• June 6th, 2002: A ~ 10 m object exploded over the Mediterranean Sea, releasing about 26 kt of energy.

– There were tensions between India and Pakistan at that time, so if this object had exploded over either country it could have sparked a war.


• Earth’s geologic record (surface and strata) shows evidence of many impacts, ranging in size from small to extinction-level events.– Most craters on Earth’s surface are

masked by weathering and foliage.• Shocked quartz is a telltale sign of an

impact site.– Examples:

• Barringer crater in Arizona• Chicxulub in the Yucatan peninsula• Newly discovered Wilkes Land crater in

Antarctica.

Background and Motivation• Barringer crater in Arizona:

– ~ 50,000 years ago.– 55 km east of Flagstaff, near

Winslow.– 1200 m wide, 170 m deep.– Caused by a nickel-iron

meteorite ~ 50 m in size.– 2.5 Mt explosion:

• All life within 4 km killed instantly.

• Everything within 22 km leveled.

• Hurricance-force winds out to 40 km.


• Chicxulub crater:– Cretacious/Tertiary (K/T) boundary

extinction event.• ~ 65 million years ago• More than 70% of species made extinct, including the

dinosaurs• Caused by the impact of a 9 – 19 km diameter NEO in

the Yucatan Peninsula near Chicxulub

Map Showing The Yucatan Location Detailed Enhanced Image Showingthe K/T Crater Edge

Topographic Enhanced Image of the180 km wide, 900 m Deep K/T Crater


• Newly discovered Wilkes Land crater in Antarctica.– ~ 480 km wide

• Believed to have been caused by a NEO up to 48 km in mean diameter.

– Likely cause of the Permian-Triassic extinction 250 million years ago.

• Confirmation pending.

• If so, the impact killed off most life on Earth at the time.– Eventually allowed dinosaurs

to flourish.Ohio State University


• Researchers have found patterns of periodic extinction in the fossil record.– 62 3 million years– 140 15 million years

• Cause for some periodic extinctions may be NEO impacts.– NEO impact did cause the K/T

boundary extinction ~65 million years ago.

Rohde & Muller, Cycles in Fossil Diversity, Letters to Nature, vol. 434, pgs. 208-210


• Apophis is the Greek name for the Egyptian God Apep, who is the God of death, destruction, and darkness.

• This asteroid will pass within ~ 30,000 km of Earth’s surface on April 13th, 2029.

• If it passes through a “keyhole” location in space, it will return to impact in Earth in 2036.– Probability fluctuates as

observations are made.

Size 320 - 400 m ¼ mile

Mass 4.61010 kg 130,000 Fully loaded 747aircraft

Impact Velocity

12.59 km/s 28,000 mph

Impact Energy

870 Mt 43,500 Hiroshima Bombs(20 Kt each)

Impact Probability

1/38,000 Comparable to death by snakebite or tornado.

2036 Apophis Collision Event Data

Asteroid 99942 Apophis (previously 2004 MN4)


• Motivation for studying and learning how to mitigate NEO collisions with Earth:– Small but dangerous NEOs collide

regularly.– Large and catastrophic NEOs have

collided in the past and will do so again.– The ability as a species to save ourselves

from this celestial threat is a true milestone.


• Early detection, accurate threat assessment, and scientific characterization are all essential to mitigation, so these are motivated also.– We already want to study NEOs to

advance solar system science and have deployed spacecraft missions to do so.

• NEAR• Deep Impact• Hayabusa (MUSES-C)

Asteroid Eros Seen During NEAR Mission

Comet Tempel 1 Stuck During Deep Impact Mission

Asteroid Itokawa Seen During Hayabusa Mission


• Congressional mandate to NASA on December 22, 2005:– "The U.S. Congress has declared that the

general welfare and security of the United States require that the unique competence of NASA be directed to detecting, tracking, cataloguing, and characterizing near-Earth asteroids and comets in order to provide warning and mitigation of the potential hazard of such near-Earth objects to the Earth.


– The NASA Administrator shall plan, develop, and implement a Near-Earth Object Survey program to detect, track, catalogue, and characterize the physical characteristics of near- Earth objects equal to or greater than 140 meters in diameter in order to assess the threat of such near-Earth objects to the Earth. It shall be the goal of the Survey program to achieve 90% completion of its near-Earth object catalogue (based on statistically predicted populations of near-Earth objects) within 15 years after the date of enactment of this Act.


– The NASA Administrator shall transmit to Congress not later than 1 year after the date of enactment of this Act an initial report that provides the following:

• (A) An analysis of possible alternatives that NASA may employ to carry out the Survey program, including ground-based and space-based alternatives with technical descriptions.

• (B) A recommended option and proposed budget to carry out the Survey program pursuant to the recommended option.

• (C) Analysis of possible alternatives that NASA could employ to divert an object on a likely collision course with Earth."

Overview


Systems Engineering

• There is no “silver bullet” solution to the NEO mitigation problem.– Each scenario is unique.– At our current level of knowledge and experience,

we can derive generalized requirements and principles.

– Actual experience gained in practicing on test NEOs will greatly improve our proficiencies:

• NEO Mitigation• NEO Science• NEO Resource Utilization

Systems Engineering

• The holistic NEO mitigation problem consists of several key phases:– Initial Detection– Threat Assessment

• Probability of impact– Threat Characterization

• NEO orbit• NEO physical properties

– Threat mitigation

Systems Engineering

• Mitigation requires:– Initial discovery of the threatening NEO.– Assessment of the threat.– Scientific characterization of the NEO.

• Thus all systems must work cooperatively.– Detection and tracking– Threat characterization– NEO physical characterization– NEO mitigation mission planning and design

Systems Engineering

• This complex problem is best treated with a Systems Engineering approach– Interdisciplinary:

• Optics and radar (detection, tracking, threat assessment)

• Orbital mechanics and Statistical Estimation Theory (NEO orbit characterization)

• Planetary science (NEO physical characterization techniques)

• Spacecraft Mission Design (physical characterization missions, mitigation missions)

Systems Engineering

• Systems:– Detection and tracking

• Optical and radar• Ground- and space-based

– Orbit modeling and impact probability assessment• Post-processing of observational data• Spacecraft transponder beacon mission deployed to NEO

– Physical characterization• Ground or space observatory data processing• Spacecraft science mission deployed to NEO

– Mitigation system• Spacecraft mitigation mission deployed to NEO

Systems Engineering

• Spacecraft systems:– Launch vehicles– Thrusters– Spacecraft bus– Spacecraft avionics (GNC)– Spacecraft science instrumentation– Spacecraft communications and data handling– NEO mitigation system– And more …

http://near.jhuapl.edu/spacecraft/

Systems Engineering

• We will focus on mitigation systems and spacecraft missions for mitigation.– Requirements follow from analysis of the general

hazardous NEO scenario.• Scenario is expressed as a timeline comprised of events.

– Each event has an associated system.

– Generalized mitigation mission architecture has been devised and will be presented.

• Requirements drive this architecture.– The most important requirement is simply this: If a

NEO is on a collision course with Earth, we must prevent the collision.

Systems Engineering

• Fault tolerance and redundancy take on critical importance in the case of a civilization-threatening NEO ( 1 km).– Robust design practices.– Multiple mitigation spacecraft and launch

systems.• In the case of a deflection, if all craft remain

operational the opportunity exists to apply multiple deflections to enhance effectiveness.

Overview


NEO Detection

• NEO discovery and cataloguing:– Detection and observations:

• LINEAR• NEAT• LONEOS• Catalina Sky Survey• Spacewatch

– Tracking and threat characterization:• Near-Earth Asteroid Tracking (NEAT) program at JPL• Near-Earth Objects Dynamic Site (NEODyS) in Pisa,

Italy

http://www.ll.mit.edu/LINEAR/

NEO Detection

• Current statistics (June 30th, 2006):– 4131 NEOs discovered thus far.

• 838 NEOs 1 km in size or greater.• 784 PHAs (orbits come within 0.05 AU of

Earth’s orbit)– Spaceguard Goal:

• Established in May 1998.• Discover 90% of NEAs 1 km by 2008.• As of 2005 we believe we’re at 73%.

NEO Detection

http://neo.jpl.nasa.gov/stats/

NEO Orbit Characterization• Orbit propagation and collision detection:

– Knowledge and classification of NEO orbits– Identification of PHAs– Determination of collision probabilities– Ground or space observatories

• Space observatories offer more coverage and better observations.

– Allows detection and characterization goals to be met much more swiftly but at higher cost.

– Transponder missions• X-band transponder:

– Position accuracies on the order of 100 m and velocity accuracies on the order of 0.1 mm/s within a geocentric distance of 2 AU, assuming a 35 m receiving dish on Earth.

– Requires 5 W of power.

NEO Threat Characterization

• Torino Scale

http://impact.arc.nasa.gov/torino.cfm


• Palermo Scale

T

PP

TPPP

B

I

B

I

10log - Palermo Scale Value

- Probability of Impact

- Annual Background Probability of Impact for a NEO with Same Kinetic Energy

- Time in Years Before Impact


• The Torino scale is intended for communicating impact risk to the general public.

• The Palermo scale is intended for impact risk communication within the scientific and engineering communities.

• Both scales rate threat by cross-referencing:– Impact energy.– Probability of impact.


• Perceived probability of impact is what matters.– We will take action based on our best estimate of

the impact probability.– We currently have not defined a probability

threshold for taking action.• Probability x Cost vs. Mission and Operations Cost?

– It is crucial to have high quality observations and prediction methods.

• Many lives or our entire civilization are at stake.• NEO mitigation missions are highly-resource intensive.

NEO Characterization

• NEO physical characterization:– Physical properties

• Mass• Density• Porosity• Internal structure and composition• Surface chemical composition• Spin state

Near-Infrared Spectrograph Used in NEAR Mission

John Hopkins University/Applied Physis Laboratory, (1998).NEAR Near-Infrared Spectrometer. Near Earth Asteroid Rendezvous. http://near.jhuapl.edu/fact_sheets/NIS.pdf

NEO Characterization

• NEO characterization– Ground or space observatory systems

• The observational data from these systems can provide estimates for a NEO’s bulk properties.

– These need to be created.

– Spacecraft science missions• On-orbit NEO science is the only way to gather

accurate and detailed physical data on the NEO.

• Such information is crucial for effective mitigation system design.

NEO Mitigation

• The primary requirement is that the incoming NEO does not collide with Earth.– If we can mitigate once and it remains a future

threat, we can mitigate it again.• The secondary requirement is that all

possible future collisions of that NEO with Earth are also eliminated.– Gravitational keyholes must be considered.

• There are three modes of mitigation: annihilation, fragmentation, and deflection.

NEO Mitigation

• Gravitational keyholes– Small regions in space near Earth defined

by the dynamics between the NEO and Earth such that:

• If the NEO passes through a given keyhole, it will be placed onto a “resonant” orbit by Earth’s gravity, causing the NEO to return to collide with Earth some number of orbits later.

– Example: 7:6 resonance – NEO orbits the sun 6 more times while the Earth orbits 7 more times and at the end of the 7th Earth orbit, the NEO collides with Earth.

NEO Mitigation

• If it is known in advance that a NEO will pass through a keyhole, it is sufficient to deflect the NEO just enough to nudge its trajectory outside of the keyhole.– Generally requires less v than a maximal

deflection.– Care should be taken to avoid other keyholes.– It is still better to move the NEO’s path such that is

passes by Earth at a great distance if possible.– Asteroid orbits that pass near keyholes are

dangerous.

Overview


NEO Mitigation Modes

• Annihilation– Reduction of NEO to vapor or fine-grain dust cloud

by energy application or pulverization.– Provides the highest assurance that the threat is

permanently eliminated.– Requires the most energy out of the three modes.– Energy requirements are generally prohibitive.– Required technologies are generally unavailable.

• Ultra high-power laser beams.• Sets of many high-yield explosives.• Antimatter torpedoes.• Series of ultra-high energy kinetic impactors.


• Fragmentation– Reduction of NEO to (hopefully) small but not

necessarily negligible pieces.– Provides assurance that the threat is permanently

eliminated only if the largest fragment is smaller than the threshold for burning up in Earth’s atmosphere (~ 20 – 50 m).

– Least controllable mitigation mode.– Medium to high energy requirements.– Examples:

• Properly placed explosives (conventional or nuclear).• Sufficiently energetic kinetic impactor(s).• Tungsten bullet “cutters.”


• Deflection– Modification of NEO’s orbit such that it misses Earth

rather than collides.– Potentially provides the least assurance that the threat is

permanently eliminated.• Gravitational keyholes.• NEO still exists.

– Most controllable mitigation mode.– Low to medium energy requirements.– Examples:

• Nuclear detonations (surface or standoff).• Attached thrusters (low or high thrust)• Solar concentrators• Gravity tractors

Overview


NEO Deflection Methods

• Deflection is the preferred mode of mitigation.– Most practical mitigation mode, given

current and foreseeable technology.• Energy requirements are tractable for a wide

range of NEOs.– Most controllable, generally.

• With practice we can develop proficiency and learn the pitfalls.

– This is absolutely critical if we are to be prepared.


• Deflection has its difficulties:– Rubble piles or highly porous NEOs.– Some proposed deflection systems are very

challenging to implement due to:• Anchoring to NEO surface.• Complex proximity operations about NEO.• NEO spin state.• Long periods of operation on orbit in hostile space

environment.– Higher probabilities of failure.

– All proposed systems are currently untested.


• Some possible deflection systems:– Gradual

• Solar concentrators• Attached low-thrust thrusters• Gravity tractor

– Impulsive• Kinetic impactors• Attached high-thrust thrusters• Nuclear explosives

– Standoff blast– Surface blast

Gritzner, et al. “Mitigation technologies andtheir requirements” Mitigation of HazardousAsteroids and Comets, Cambridge UniversityPress, 2004

Conceptual Solar Collector Design


• Nuclear explosives offer the following advantages:– NEO spin state not a factor.– No anchoring of equipment to NEO.– No long operation on orbit.– Highest available energy density.

• High capability for imparting momentum to a NEO.– High energy density equates to easier launch

from Earth.• Multiple launches are more feasible.


– High momentum transfer performance:• Can adequately deflect larger NEOs than other

methods even with limited warning time.– Technology is currently available.– Puts former weapons of mass destruction

to a use that benefits all humankind.– Deflection is relatively controllable through

proper positioning of the device prior to detonation.


• Nuclear explosive disadvantages:– Untested.– Required rendezvous and proximity

operations are challenging in some cases.– Requires special packaging inside launch

vehicle to ensure containment in the event of launch vehicle failure.

– Danger of inadvertently fragmenting NEO in an undesirable fashion.


– Sensitive to NEO physical properties.• In the absence of good knowledge of NEO

physical properties, the system must be over-designed.

– Requires amendment of the “Nuclear Test Ban Treaty” (1963).

– Public fear and misunderstanding.– Political tensions.


• Standoff nuclear detonation:– Nuclear device of proper yield

is placed at the optimal detonation coordinates.

• Optimal distance from NEO surface.

• Optimal orientation of imparted impulse vector.

– Neutrons from the explosion penetrate 10-20 cm into NEO surface, superheating a thin shell of NEO material.

– Material blows off and imparts momentum to NEO.

Artist’s Conception of a Standoff Nuclear Detonation Applied to an

Asteroid

Ahrens, Thomas J. and Harris, Alan W., “Deflection and Fragmentation ofNear-Earth Asteroids,” Hazards Due to Comets & Asteroids: 909 – 913. 1994

Wilkins, Peter A. Computer rendering of asteroid model usingLightwave software (November 2005)


D

y

sd

P

eA

Quantity Value

Neutron penetration depth, 20 cm

Mean NEO density, 2.65 g/cm3

NEO diameter (spherical NEO), 1000.0 m

Nuclear device yield, 1 Mt

Optimal standoff detonation distance, 23 m

Momentum imparted to NEO, 1.41010 kg-m/s

Percent of NEO surface area affected, 2.2%

Percent of total neutron energy absorbed 35%

Specific energy below detonation point, 1200.0 MJ/kg

Energy per unit mass of NEO material, 100 J/kg

Imparted velocity change, 1 cm/s

l

Q

spE

v

Standoff Nuclear Detonation Modeling For a 1 km Asteroid

Imparted Momentum to 1 km NEO Test Cases

Holsapple, Keith A. “About deflecting asteroids and comets”Mitigation of Hazardous Asteroids and Comets, CambridgeUniversity Press, 2004

Overview


Optimal Deflection

• A deflection must applied in an optimal fashion.– Imparted momentum is tiny compared to

the NEO’s momentum.– Application must be optimal in order to

ensure effectiveness.– There are impulse vector orientations that

have little or no effect on the NEO’s subsequent motion.

OriginalTrajectory

PerturbedTrajectory

NEO

OriginalTrajectory

PerturbedTrajectory

NEO

OriginalTrajectory

PerturbedTrajectory

NEO NEO Body

NEO Centerof Mass

r̂

t̂

n̂

NEO Body

NEO Centerof Mass

r̂

t̂

n̂

NEO Body

NEO Centerof Mass

r̂

t̂

n̂

- azimuth- elevation

- azimuth- elevation

• Impulsive deflection is applied at a particular point along the NEO’s orbit, at a particular time before Earth impact.

• Impulse immediately alters the NEO’s heliocentric velocity.

• Impulsive velocity change vector is parameterized.

– It is always optimal to maximize the magnitude of the imparted velocity change, and this is a function of NEO properties and mitigation system technology.

Impulsive NEO DeflectionProblem Setup

trtrtr EARTHNEO

trtrtr EARTHNEO

EARTHcoll Rtr EARTHcoll Rtr

CACA tttt CACA tttt 0

00

CA

CA

CA

trtrtr

0

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CA

CA

trtrtr

colltcollt

CAtCAt

collCA

collCA

ttbut

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collCA

ttbut

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CAt CAt,CAt CAt,CAt CAt,

Sun

Earth

NEO

HCIX

HCIY

HCIZ

Sun

Earth

NEO

HCIX

HCIY

HCIZ

Sun

Earth

NEO

HCIX

HCIY

HCIZ

trtr trtr

EARTHRtr EARTHRtr

Collision Condition:

NEO-Earth Distance:

Position Vector of NEO with respect to Earth:

Deflection Condition:

~ small

= original (unmitigated) time of collision

= time of closest approach after mitigation

A deflection may be interpreted as:The forced transition of a collision event toa close approach event.

Optimal Deflection

EARTHR

r

t

EARTHR

r

t

DEFtCAtcollt

P

DeflectedTrajectory

UndeflectedTrajectory

DEFt

P

CAt EVENTt

Case 1:Original “event” isa collision.

Case 2:Original “event” isa close approach.

* Note: Figures not to scale.

DeflectedTrajectory


EARTHR

r

t

EARTHR

r

t

EARTHR

r

t

EARTHR

r

t

DEFtCAtcollt

P

DeflectedTrajectory


DEFt

P

CAt EVENTt

Case 1:Original “event” isa collision.

Case 2:Original “event” isa close approach.

* Note: Figures not to scale.

DeflectedTrajectory


CADEF tttt CADEF tttt

EVENTt EVENTt

There is a restriction on the range oftimes over which the performanceindex is evaluated.

Performance index:

* = time of original (unmitigated) close approach “event”

Optimal Deflection

finalresinitscan

finalresinitscan

finalresinitscan tttt

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DUNDEFLECTEDEFLECTED trtrP minmin

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Simulationsof

Dynamics

OPTIMAL SOLUTION

Design Space:

Optimal Deflection

Optimal Deflection

• Two case studies were performed to assess the effectiveness of this methodology.– First case study examined azimuth and

elevation angle effects.– Second case study examined time of

deflection effects.• This case study also utilizes the NEO mitigation

mission design architecture that will be presented later.

Optimal Deflection

• First case study:– Real asteroid: 1991 RB

• Asteroid closely approached Earth.• Goal is to maximally increase close approach

distance.– Previous research used linearized

dynamics and eigenspace analysis to optimize impulsive deflections.

• Linearization constrains time of deflection to be during NEO’s final solar orbit prior to impact or close approach.

Optimal Deflection

• Comparison of methodologies:– Different performance indices.– Different dynamics models.

• Current work uses n-body simulation including the Sun, NEO, and Earth.

– Current methods do not employ linearizations.

– Both methods found that optimal impulse vectors lie in the NEO’s orbit plane.

Optimal Deflection

0

0

0

00 ~

~,

vr

VVRR

vr

ttvr

00 tvRtr

CAtrP

DUNDEFLECTECANEODEFLECTEDCANEO trtrP

DEFtt 0

vv 0

State transition matrix (Battin 1987):

Change in position due to a change in velocity:

Performance index:

Performance index in the currentnotation:

Relationship to the current notation:

Point at whichdeflection is applied

NEO on perturbed trajectory

NEO on unperturbed trajectory

Perturbed trajectory

Unperturbed trajectory

Previous Research Performance Index

P

Optimal Deflection

Orientations of Optimal Deflection Impulse Vectors

Magnitudes of Optimal Deflections

Asteroid Physical Parameters:Mean diameter ……………………….. 500 – 1100 mAvg. mean diameter …………………. 800 mAssumed mean density ……………… 2.7 g/cm3

Computed mass (spherical model) …. 7.241011 kg

1.4544 AU

0.4856

19.5929359.482468.7619306.7261

a

e

iM

Epoch: 8/18/2005, 00:00:00 UT

JPL Orbital Elements for Asteroid 1991 RB

1v m/s

Time Before Close Approach of Asteroid to Earth [days]

Estimated Deflection from Graph [km]

19 1700

72 7700

134 18400

Optimal deflections are computed such that the asteroid deflection is maximized on September 19 th, 1998.

B.A. Conway “Optimal interception and deflection of Earth-approaching asteroids usinglow-thrust electric propulsion” Mitigation of Hazardous Asteroids and Comets,Cambridge University Press, 2004

Optimal Deflection

Deflection [km] Angle from Asteroid

Velocity Vector

Azimuth Angle in RTN Frame

Current 18182.3 96.8 240

Previous 18400 93 -

Deflection [km] Angle from Asteroid

Velocity Vector


Current 18181.5 83.2 60

Previous 18400 93 -

Optimal Solution

Near-Optimal Solution

DUNDEFLECTECANEODEFLECTEDCANEO trtrP

Case (a): Using Previous ResearchPerformance Index

* Solution space appears to show two nearly identical optimal solutions.

* Solution space also shows two nearly identical worst solutions, and both appear to still successfully move the asteroid further away from Earth.

Optimal Deflection

Deflection [km]

Angle from Asteroid Velocity Vector


Current 15464.6 104.2 81

Previous 18400 93 -

* Achieved deflection is 16% less than that found by previous study.

* Optimal orientation of the deflection impulse vector differs by 10%.

Optimal Solution

* Solution space shows one distinct optimal solution.

* Solution space shows one distinct anti-optimal solution that actually pushes the asteroid closer to Earth.

* Solution space shows two solutions that have zero effect.

Case (b): Using Current Performance Index

Structure of Solution Space UsingCurrent Performance Index

Optimal Solution

Zero-Effect Solutions

Anti-Optimal Solution

Optimal Deflection

- Optimal elevation angle is zero.- There is a spread of about ±20-30° about the optimal elevation angle for which most (~ 90%) of the maximal deflection is still achieved.

Elevation Angle Effects

Optimal Deflection

• There is a spread of azimuth angles, approximately ±15-20°, about the optimal for which most (~90%) of the maximal deflection is still achieved.

Azimuth Angle Effects

Optimal Deflection

• Conclusions:– Optimal deflections performed shortly

before impact may have significant radial components.

– Optimal deflection impulse vectors lie in the NEO’s orbital plane.

– There is a moderate range of angles about the optimal for which most of the deflection is still achieved.

Overview


NEO Scenario Timeline

• A general hazardous NEO scenario has a timeline associated with it.– Events ranging from initial detection to

Earth collision, if threat goes unmitigated.– Analysis indicates steps that will maximize

our chances of successful mitigation.– Lays foundation for requirements

derivation and mitigation mission planning.


Forward Time

NEO Detected

- NEO determined to be a threat- Mitigation mission planning begins

- Mission planning reaches critical mass- Construction of spacecraft and preparation of launch vehicle begin

Spacecraft carryingthe chosen mitigationsystem launches

Spacecraftperformsrendezvouswith NEO

Mitigation systemis positioned andprepared foractivation

Time of UnmitigatedEarth Impact

Continuum of availabledeflection times

NEO Collision Mitigation Timeline

* These two events may be collapsed into one event, which is Interception, depending on the Mitigation system requirements


• Goal is to maximize the Continuum of Available Deflection Times:– Generally, the earlier a deflection can be applied, the

more effective it will be.– Steps:

• Detect all NEOs as early as possible.• Minimize time to determine if a given NEO is a threat.• Minimize Mission Planning Time.• Minimize Spacecraft / Launch Vehicle construction and

preparation time.• Optimize rendezvous or interception trajectory according to:

– Minimum Flight Time– Optimal Deflection Principles– Fuel / Technology Constraints


• System requirements– Detection Systems

• Long range, high-resolution, view as much of the sky as possible.

– Space-based systems achieve these requirements better than ground-based systems.

– Characterization Systems• High accuracy

– Ground- or Space-based system improvements (radar & optical).

– Development of rapid deployment, low mass x-band transponder beacon placement missions.

» On NEO body» On NEO orbit


– Mitigation Mission Planning• Develop comprehensive means of devising efficient and

effective (tend towards optimized) mitigation missions.– Spacecraft / Mitigation System Construction

Systems• Develop proficiency with the operation of various mitigation

systems.– Field tests during non-emergency times.

• Spacecraft and mitigation equipment components should be modular and able to be assembled reliably in rapid fashion.

– Mitigation Spacecraft Launch System• Able to be constructed and prepared for launch rapidly so

as to be able to take advantage of earliest launch window.


• We don’t necessarily want to have pre-built mitigation systems on standby.– Collision of dangerous NEOs is a low-frequency

event.– Maintenance costs.– Uniqueness of NEO scenarios requires custom

designs.– We can still improve our rapid deployment skills

and develop modular systems that have both mitigation and other applications.

• NEO Science• NEO Resource Utilization

Overview


Mission Design Architecture

• NEO Mitigation Mission Planning Architecture:– Three phases:

• Detection and Reconnaissance• Design Cycle (Iterative)• Execution

DetectionAnd

ReconnaissanceDesign Cycle Execution

ITERATE UNTILWORKING DESIGN

IS REACHED

ITERATE FURTHERFOR OPTIMIZATION


Design Cycle

Detection & Reconnaissance

Estimate NEO PhysicalProperties From Ground

Observations And ComputerModels

Accurate PhysicalProperties Obtained

NEO Orbit IsAccurately Known

Use Estimate of NEOOrbit From Ground

Observations

Simulate NEO OrbitAs Accurately As

Possible

Will NEO IndeedCollide With

Earth?

NEO is Discoveredwith Non-Zero Probability

of Earth Collision

Estimate EarthCollision Time

START

Send ScienceMission To NEO

Create The MostAccurate Physical

Model Of NEO Possible

STOP

Is There EnoughTime For APreliminary

Science Mission?

Is There EnoughTime To Deliver A

Transponder BeaconTo The NEO?

Send BeaconMission To NEOYES

NO

NONO

NO

YES

YES

Mission Design ArchitectureDesign Cycle

Select NEOMitigation System

Execution

Does Mass BudgetAllow For Science/Beacon Equipment

To Gather Pre-And Post-

Mitigation Data?

Does Payload MassRequire On-Orbit

Assembly?

Maximum MitigationPotential Is Fixed

Determine OptimalMitigation Operations

Determine LaunchWindows For NEO

Rendezvous OrInterception

Determine NEORendezvous Or

Interception TrajectoryAnd Maneuvers

Determine ThrusterAnd Fuel

Requirements

Design Spacecraft ToDeliver And OperateMitigation System

Determine TotalLaunch Payload Mass

Determine RequirementsFor Launch Vehicle(s)

Design SpacecraftAnd Equipment For

Science To Be Included With

Mitigation Mission

Design On-OrbitAssembly Mission

Phases and Spacecraft

Knowledge Of NEO Physical Properties Knowledge of NEO Orbit

YES

YES

TOP LEVEL OF DESIGN CYCLE


Re-Enter Design CycleAt TOP LEVEL

ExecutionRequirements for Launch Vehicle(s)

Is MissionFeasible?

EXECUTEMISSION

Finalize Mission Phases AndMission Objectives And

Develop Contingency Plans

Make Final Selection(s) Of Launch Vehicle(s)

YES

NO

To TOP LEVEL Of Design Cycle


• Following this mission design process will produce effective missions.– However, we must accept that scenarios

theoretically exist for which there is no mitigation solution due to technological and/or timing constraints.

• In this case we must follow other contingency procedures, such as evacuation and/or sheltering, depending on the level of threat.


• Second case study:– Applies mitigation mission design

architecture.• Proceeds through one iteration of the design

cycle.• Each component of the design cycle is treated

to first order.• A working solution is achieved after one

iteration, and further optimization is possible.– Examines time of deflection effects.


• A complete mission plan to deflect a fictitious NEO is devised.• The fictitious NEO parameters are taken from a document

entitled “Athos, Porthos, Aramis & D’Artagnan: Four Planning Scenarios for Planetary Protection” by David K. Lynch, Ph.D. and Glenn E. Peterson, Ph.D. of The Aerospace Corporation.

– The purpose of the document is to present four characteristic NEO impact scenarios so that mission planners can devise solutions.

Given Scenario Parameters:Asteroid name ………………… D’ArtagnanDate of Discovery …………….. February 22nd, 2004, 00:00:00 UTDate of Earth Impact …………. September 14th, 2009, 11:04:26.117 UTShape ………………………….. EllipsoidalDimensions ……………………. 110120 130 mDensity ………………………… 4.0 g/cm3

Computed Asteroid Mass ……. 3.594109 kgCompositional Type ……………S (silicaceous)Orbit Type ……………………... Aten

Mission Design ArchitectureImpact Location ………………… Lyon, FrancePopulation at Impact Location….415,000 (city proper) / 1.26 million (urban area)Impact Velocity ……..………….. 14 km/sImpact Energy ………………….. 84 Mt

* For reference, the largest nuclear bomb ever tested on Earth had a yield of 50 Mt.

Idealized Structural Diagram of Asteroid D’Artagnan

Computer-generated Model of Asteroid D’Artagnan

height, = 110 m

width, = 120 m length, = 130 m

h

lw

Wilkins, Peter A. Computer rendering of asteroid model usingLightwave software (November 2005)


a

e

i

M

Approximate Value

Computed Value

0.8976 AU 0.8995 AU

0.288063 0.2822

4.788754 4.521

350.540144 351.897

230.740220 231.071

254.275083 271.975

D’Artagnan’s Orbital Elements at the Time of Detection

D’Artagnan and Earth Orbits in The Ecliptic Plane

NEO Orbit


Perceived Impact Probability and Corresponding Threat Rating as a Function of Observed Data Arc

• A case study performed by Chesley, et al found that it took approximately a year of continuous observation to determine that a simulated impacting asteroid had a high probability of Earth impact (~ > 50%).

• Their simulated impactor was 17 years out and D’Artagnan is only 5 years out so orbit propagation errors would be less.

• It will be assumed that D’Artagnan is perceived to have an alarming probability of impact (> 50%) by 6 months after initial discovery. Mitigation mission planning begins at this point.

Time Until D’Artagnan is Determined to be a Threat

Chesley, et al. “Earth impactors: orbital characteristics and warning times”Mitigation of Hazardous Asteroids and Comets, Cambridge University Press, 2004

Mission Design Architecture• It is assumed that a mitigation mission can be designed and a

spacecraft readied for launch by one year after initial threat determination.– The NEAR Shoemaker mission went from concept to launch in

three years.– Mitigating D’Artagnan is an emergency situation so it is assumed

that work will proceed much faster.• Since the impact is only about 4 years away by the time a

spacecraft can be prepared, there is no time for a preliminary science mission.– Mission planners are forced to use estimates of D’Artagnan’s

physical parameters based on ground observations.• Mission planners choose to use a standoff nuclear detonation to

deflect D’Artagnan.– Technology is readily available and mission complexity is

minimized.


Temporal Maximized Deflection Map with Perihelion Passages Marked by Red Arrows

Deflection as a Function of Azimuth for Various Deflection Times

Deflection Optimization Results for a Velocity Change Magnitude of 5.0 cm/s

• It is hoped that the spacecraft can deliver the nuclear device to the asteroid within 1 year of launch.• Deflection times are scanned at a resolution of 5 months, beginning at 2.5 years from the time of initial detection.• Times for which D’Artagnan is at perihelion are included.• The elevation angle is set to zero and azimuth angles are scanned at a 1 resolution.


- Deflections applied at perihelion passages clearly yield the best deflections.- The best overall deflection occurs at the perihelion passage about 2.75 years after initial detection.-Thus the chosen time of deflection is about 2.75 years after initial detection, which is 15 months after mitigation spacecraft launch.

Optimal Impulse Vector Azimuth …. 182 (178.06 apart from asteroid velocity vector)Optimal Time of Deflection …………11/28/2006, 14:24:00 UT (2.767 years after detection)Deflection Magnitude ………………. 10487 km (~ 1.64 Earth radii)

Deflection Optimization Results for a Velocity Change Magnitude of 5.0 cm/s

Deflection Optimization Summary


• Time from detection to threat determination …………… 0.5 years• Time from detection to mitigation spacecraft launch …. 1.5 years• Time from detection to deflection ………………………. 2.767 years

• Deflection velocity change magnitude ………………… 5 cm/s• Nuclear device and yield …………………………………68 Kt (W-85)

• Optimal deflection azimuth angle ………………………. 182 (178.06 from velocity vector)• Optimal time of deflection ……………………………….. 11/28/2006, 14:24:00 UT• Optimized deflection distance …………………………… 10487 km

• Launch vehicle ……………………………………………. Boeing Delta IV Heavy• Rendezvous Thruster ……………………………………. Pratt & Whitney RL 10• Proximity Operations Thrusters ………………………… DASA CHT Monopropellant

• Launch Date ………………………………………………. 8/25/2005• Arrival Date ……………………………………………….. 10/8/2006• Time of Flight ……………………………………………… 13.733 months• Spacecraft Launch Mass ………………………………… 7960 kg• Spacecraft Arrival Mass ………………………………….. 820 kg

• Optimal Standoff Detonation Distance …………………. 2.76 m• Time available to Position Nuclear Device …………..… 51.6 days

Mitigation Mission Design Results


• The principle is that optimized missions may be developed by:– Optimizing each component in the process

to the extent possible.– Iteration of the Design Cycle.

• Sampling the design space is required, so making some a priori assumptions makes the process more efficient.– Establish general principles.

Mission Design Architecture• Generally, the best time to deflect is the first

logistically available perihelion passage of the NEO.– Optimal deflecting impulse vector characteristics:

• Lies in the NEO’s orbit plane.• Is close to opposite the NEO’s velocity vector for deflections

applied with at least a few years of lead time.• Has more radial component when deflection is applied with little

lead time.• There is an appreciable spread of orientations about the optimal

for which most of the maximum deflection is still achieved.– Robust.

• Is best determined by formulating the problem using the performance index presented herein and using detailed dynamics models.

Overview


Conclusions

• Ongoing work:– Deflection system research and design.

• Develop and TEST viable mitigation technologies.

– Optimization of overall mitigation system.• Hybrid Optimal Control Theory

– Categorical variables.– No a priori assumptions.

– Cost modeling for various example mitigation missions.

Conclusions

• Ongoing work:– Cost modeling for actual missions that will

test mitigation systems and simultaneously gather NEO science data as per usual.

– Selection of target asteroids for mitigation system testing.

• Safety.• Scientific interest.

– Define perceived impact probability thresholds for taking action.

Conclusions

• Detection and Characterization systems must be maintained, enhanced, and expanded:– Space-based observatories– More NEO science missions

• Combine these with mitigation missions for synergy.

– Might even combine with resource utilization technology test missions for additional synergy.

– Rapid-deployment beacon mission development.

Conclusions

• Continue and enhance NEO science missions.– Incorporate mitigation system tests.– Build proficiency.– Learn the pitfalls.– Demonstrate that we as a species have the

ability to mitigate the hazard posed by an incoming NEO.

• True species milestone.

Questions?

http://www2.jpl.nasa.gov/sl9/image81.html

brent william barbee, m.s.e. emergent space technologies, inc

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