LUTH, Meudon, 21.02.2013Siegfried Eggl

Asteroid Deflection - Why Bother?

Chelyabinsk 15.02.2013

D=7-17m

M~7000 t

Shallow entry

Asteroid Deflection - Why Bother?

D~45m

M~???

Missed...

MPC 2013

Currently Known NEOs > 1km: (1268)

Aerospaceweb.org

Asteroid Deflection - Why Bother?

1. Where do NEOs come from?

2. How many are there?

3. How many are dangerous?

4. What can we do about them?

Currently Asked Questions

Near Earth Object Family Tree

Solar System Minor Planets

NEO: within Mars orbit (9614)

Space Debris

Near Earth Comets

Near Earth AsteroidsPHO (1377)

IAU MPC 16.02.2013

Where do NEOs come from?

NEO lifetime ~ 106 yrs, constant replenishment necessary

~600 000 MBOsNEO lifetime ~ 106 yrs

Yarkovsky Thermal Effect

diurnal seasonal

Bottke et al. 2006

~600 000 MBOs

How many NEOs are there?

What percentage do we know?

NEO numbers

IAU MPC 16.02.2013

NEOs: 9614

NEOs > 1km: 1268

PHOs: 1377

Is that „all“?

Wide-field Infrared Survey Explorer

NASA mission 2010, 40 cm optics ,IR : 3-25 μm

NEOWise (PI: Mainzer, A.)

Wide-field Infrared Survey Explorer

Discovery Totals

NEAs: 129PHAs: 21

Comets: 17Total: 146

How many are potentially dangerous?

Potentially Hazardous Objects

PHOs (1377) : MOID <0.05 AU,

H<=22mag (D<150m)

Minimum Oribt Intersection Distance

PHO (1377) : MOID <0.05 AU, H<=22mag

(D<150m)

http://orsa.sourceforge.net/atwork.html

JPL 2013

JPL 2013

How dangerous are PHOs?

Torino Scale:

0-10: according to impact risk

and impact consequences

Palermo Scale:

compare risk of individual impact

probability to background

(LOG)

The Palermo Scale

PS= log10 R R...Relative Risk

R=PI / (f x DT) PI ...Imp. Prob. DT...Time to Imp. f .....BG Imp. Prob.

f= 0.03 x E -4/5 E...Imp. Energy (Mt)

Object Palermo Torino

Apophis -3.33 0

2007 VK184 -1.57 1

Impact probability?2 body scattering

b... Impact parameter

b

Impact probability

orbit uncertainty

Impact probability: 1/3

Clones

Impact probability 3D

b-plane

Uncertainty Ellipse

Keyholes, 99942 Apophis

Bancelin (2012)

x 10

0 [k

m]

[km]

b-plane 2029

Line Of Variation2011 AG5

Yeomans et al. (2012)

σζ

σξ

b-plane

LOV

a: 1.43 aue: 0.39i: 3.7°H: 21.86

Yeomans et al. (2012)

2011 AG5 close encounter 2023

What can we do?

TOO EXPENSIVE

NEOShield

•study mitigation concepts (science+industry)

•mitigation prerequisites (asteroid physical properties, orbital uncertainty)

•prepare for demo-mission

•propose international emergency strategy

•study mitigation concepts (science+industry)

•mitigation prerequisites (asteroid physical properties, orbital uncertainty)

•prepare for demo-mission

•propose international emergency strategy

What can we do?

Teaches us a lesson not to focus all attention on one object...

Tim Warchocki, National Research Council Report (2010)

NeoShield

Gravity TractorBlast Deflection

Impactor +Solar Sail+Ion Beam Shepherd

Kinetic Impactor

Kinetic Impactor

Naïve calculation

Momentum delivered by impactor = mimpact. ΔV

Momentum change of NEO = MNEO δvNEO

mimpact. ΔV = MNEO δvNEO

So mass of impactor required, mimpact. = MNEO δvNEO / ΔV

NEO: D = 150 m, density = 2.0 g cm-3, DT = 10 years,

miss distance required = 3 x R_Earth, ΔV achievable = 10 km s-1,

mimpact. = 21 tonnes!

(cf. Ariane 5 payload capacity: 10 metric tons to GTO).

Kinetic Impactor

Somewhat less naïve calculation

mimpact. = MNEO δvNEO / (ΔV x β),

β …. “momentum multiplication factor” due to momentum carried off by the collision ejecta.

NEO: D = 150 m, density = 2.0 g cm-3, DT = 10 years, miss distance required = 3 x R_Earth, ΔV achievable = 10 km s-1,

β = 5??:

mimpact. = 4.3 tonnes (cf. previous 21 tonnes with β = 1)

(cf. Ariane 5 payload capacity: 10 metric tons to GTO).

??? β ???

AVOID DESTRUCTION OF NEO!!!

Kinetic Impactor

Numerical Simulations

Laboratory ExperimentsJutzi, Benz, Michel (2008)

Deep Impact (NASA, 2005)Target: Comet 9P/Tempela: 3.124 au, e: 0.517, i: 10.5° m: 7-8 1013 kg

Impactor mass: 384kgChange in pericenter: 10mChange in Period: 1s

Kinetic Impactor

Two test mitigation mission proposals in Europe:

•Don Quichote (Deimos, Belló et al. (2003), NEOShield) Single Asteroid

•AIDA/DART (Cheng, A. F., Rivkin, A., Galvez, A., et al. 2012. ) Binary Asteroid

DON‘T TARGET/PRODUCE PHOs!

• Achieve high ΔV (retrograde orbit, hit NEO at pericenter, impactor mass…)

• Yet low enough ΔV for accurate targeting: auto GNC!

• Avoid destruction

• Need prior information on NEO (spin, structure, mass)

• Full phase for targeting

Kinetic Impactor Difficulties

Saks et al. (2012)

Blast Deflection

Blast Deflection vs Kinetic Impactor

mass of kinetic impactor = 4.3 tonnes , ΔV = 10 km s-1,

K.E. = 2.1 x 1011 J ~ 5.0 x 10-5 Mt (1 Mt = 4.184×1015 J).

Yield of largest H-bomb tested ~ 50 Mt! (1961).

R-36 Russian ICBM ~ 20 Mt to LEO

Even if not all of the energy will be imparted on NEO, still “afterglow” propulsion

Limiting NEO diameter ~ 3 km

Why Not Nuke Everything?

•Non weaponization of space (Outer Space Treaty)

•Avoid destruction (radioactive debris!)

•Prior information on NEO composition needed

•Not tested at all (buried, surface, stand-off blast?)

Gravity Tractor

Gravity Tractor

Gravity between NEO and Spacecraft acts as tow-rope

Big advantages: No contact, no prior knowledge of NEO composition needed.

Challenges: Very feeble acceleration, very tricky station keeping close to NEO (acc ~r-2), need precise shape/rotation model, no thrusting onto NEO, binarity!

LONG TIMESCALE/PRE KEYHOLE MEASURE

GLOBAL ISSUES

•Finding PHAs (sky coverage)

•Determination of NEO orbit

•Advance determination of NEO properties

•Getting Reconnaicance/Mitigation Missions there in time.

V=18

V=21

Orbit Determination

CEU: Current Ephemeris Uncertainty

Arc <10 days

250 days

Priority List Of Obs RequirementsPre-Mitigation Reconnaissance

Observational techniques

Relevant propertiesto estimate impact probabilities, and timeframes

High priority: Orbital state vector Absolute Magnitude

Ground / SpacePhotometryAstrometryRadarLidarFlybyRendezvous

Data-mining

Low priority:

Mass Multiplicity Spin rate Spin orientation Shape Thermal properties Albedo/Surface properties

+ Spectroscopy

PRIORITY OF NEO PROPERTIES FOR ORBIT REFINEMENT

Transfer Time

S/C rendez-vous missions offer great state vector accuracy but it takes some time to get them there.(delta v calculated following Shoemaker & Helin 1978)

CONCLUSIONS

NEOs pose a threat – which can be mitigated, if we are prepared.

NEOShield: • Comprehensive study of NEO mitigation (Industry+Science)• 3+ mitigation techniques studied in detail• Demo missions are suggested• Global issues are identified • An international mitigation strategy shall be proposed

Merci pour votre attention!

Scott Manley