LUTH, Meudon, Siegfried Eggl

Asteroid Deflection - Why Bother? Chelyabinsk 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 Asteroids PHO (1377) IAU MPC

Where do NEOs come from? NEO lifetime ~ 10 6 yrs, constant replenishment necessary

~ MBOs NEO lifetime ~ 10 6 yrs

Yarkovsky Thermal Effect diurnal seasonal Bottke et al. 2006

~ MBOs

How many NEOs are there? What percentage do we know?

NEO numbers IAU MPC NEOs: 9614 NEOs > 1km: NEOs > 1km: 1268 PHOs:1377 Is that „all“? 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

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)

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= log 10 RR...Relative Risk R=P I / (f x DT) P I...Imp. Prob. DT...Time to Imp. f.....BG Imp. Prob. f= 0.03 x E -4/5 E...Imp. Energy (Mt) ObjectPalermoTorino Apophis VK

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, Apophis Bancelin (2012) x 100 [km] [km] b-plane 2029

Line Of Variation 2011 AG5 Yeomans et al. (2012) σζ σξ b-plane LOV a: 1.43 au e: 0.39 i: 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 Tractor Blast Deflection Impactor +Solar Sail +Ion Beam Shepherd

Kinetic Impactor

Naïve calculation Momentum delivered by impactor = m impact. ΔV Momentum change of NEO = M NEO δv NEO m impact. ΔV = M NEO δv NEO So mass of impactor required, m impact. = M NEO δv NEO / 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, m impact. = 21 tonnes! (cf. Ariane 5 payload capacity: 10 metric tons to GTO).

Kinetic Impactor Somewhat less naïve calculation m impact. = M NEO δv NEO / (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??: m impact. = 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 Experiments Jutzi, Benz, Michel (2008)

Deep Impact (NASA, 2005) Target: Comet 9P/Tempel a: au, e: 0.517, i: 10.5° m: 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 ) 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 J ~ (1 Mt = 4.184×10 15 J). K.E. = 2.1 x J ~ 5.0 x Mt (1 Mt = 4.184×10 15 J). Yield of largest H-bomb tested ~ ! (1961). 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) 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?) Not tested at all (buried, surface, stand-off blast?)

Gravity Tractor

Gravity between NEO and Spacecraft acts as tow-rope Big advantages: No contact, no prior knowledge of NEO composition needed. -2 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 Requirements Pre-Mitigation Reconnaissance Observational techniques Relevant properties to estimate impact probabilities, and timeframes High priority:  Orbital state vector  Absolute Magnitude Ground / Space Photometry Astrometry Radar Lidar Flyby Rendezvous 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