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LUTH, Meudon, 21.02.2013 Siegfried Eggl. Asteroid Deflection - Why Bother?. D=7-17m M~7000 t Shallow entry . Chelyabinsk 15.02.2013. Asteroid Deflection - Why Bother?. D~45m M~??? Missed. MPC 2013. Asteroid Deflection - Why Bother?. Currently Known NEOs > 1km: (1268).
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LUTH, Meudon, 21.02.2013 Siegfried Eggl
Asteroid Deflection - Why Bother? D=7-17m M~7000 t Shallow entry Chelyabinsk15.02.2013
Asteroid Deflection - Why Bother? D~45m M~??? Missed...
Asteroid Deflection - Why Bother? Currently Known NEOs > 1km: (1268) Aerospaceweb.org
Currently Asked Questions Where do NEOs come from? How many are there? How many are dangerous? What can we do about them?
Near Earth Object Family Tree IAU MPC 16.02.2013
Where do NEOs come from? NEO lifetime ~ 106 yrs, constant replenishment necessary
~600 000 MBOs NEO lifetime ~ 106 yrs
Yarkovsky Thermal Effect diurnal seasonal Bottke et al. 2006
How many NEOs are there? What percentage do we know?
NEO numbers NEOs: 9614 NEOs > 1km: 1268 PHOs: 1377 Is that „all“? IAU MPC 16.02.2013
Wide-field Infrared Survey Explorer NASA mission 2010, 40 cm optics ,IR : 3-25 μm NEOWise (PI: Mainzer, A.)
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
How dangerous are PHOs? Palermo Scale: compare risk of individual impact probability to background (LOG) Torino Scale: 0-10: according to impact risk and impact consequences
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)
Impact probability? 2 body scattering b b... Impact parameter
Impact probability Clones orbit uncertainty Impact probability: 1/3
Impact probability 3D b-plane Uncertainty Ellipse
Keyholes, 99942 Apophis b-plane 2029 x 100 [km] [km] Bancelin (2012)
Line Of Variation 2011 AG5 σζ b-plane LOV σξ a: 1.43 au e: 0.39 i: 3.7° H: 21.86 Yeomans et al. (2012)
2011 AG5 close encounter 2023 Yeomans et al. (2012)
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 Blast Deflection Gravity Tractor +Solar Sail +Ion Beam Shepherd Impactor
Kinetic Impactor Naïve calculation Momentum delivered by impactor = mimpact.ΔV Momentum change of NEO = MNEOδvNEO mimpact.ΔV = MNEOδvNEO So mass of impactor required, mimpact. = MNEOδvNEO / 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. = MNEOδvNEO / (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 Jutzi, Benz, Michel (2008) Laboratory Experiments
Deep Impact (NASA, 2005) Target: Comet 9P/Tempel a: 3.124 au, e: 0.517, i: 10.5° m: 7-8 1013 kg Impactor mass: 384kg Change in pericenter: 10m Change 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!
Kinetic Impactor Difficulties • 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 Saks et al. (2012)
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?)