LUTH, Meudon, 21.02.2013 Siegfried Eggl. Asteroid Deflection - Why Bother? Chelyabinsk 15.02.2013...
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Transcript of LUTH, Meudon, 21.02.2013 Siegfried Eggl. Asteroid Deflection - Why Bother? Chelyabinsk 15.02.2013...
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