1 Near-Earth objects – a threat for Earth? Or: NEOs for engineers and physicists Lecture 8 – Deflection missions in detail Prof. Dr. E. Igenbergs (LRT) Dr. D. Koschny (ESA) Image credit: ESA

News Workshop on 2011 AG5 took place at Goddard Space Flight Center on 29 May AG5 is highest on risk list – 1:500. But: low confidence No need to act now. Observations in 2013 will be timely enough A 2 nd preparation meeting for the ‘Space Mission Planning and Advisory Group (SMPAG)’ took place in Vienna, last Friday 15 participants from international space agencies (ESA, NASA, JAXA, China, Russia, Iran, Switzerland, CNES, Romania…) Discussed ‘Terms of Reference’ for the SMPAG “Action Team 14” discussions on how to set up a global impact response network took place Monday/Tuesday 11/12 June

3 Context Mitigatio n preparati on Mitigatio n preparati on

Outline How far do we need to deflect? Overview of possible deflection missions In detail: The Ion-Beam Shepherd In detail: The kinetic impactor (if time)

The b-plane The ‘b-plane’ (body plane) is the plane going through the center of the Earth and perpendicular to the incoming velocity vector of the asteroid outside the sphere of influence

Apophis flyby geometry

Apophis b-plane

D. Bancelin (2011) Keyholes for Apophis

D. Bancelin (2011) Keyholes for Apophis in the b-plane

Asteroid does not hit Earth (miss distance is n * R earth where n is still tbd) Asteroid does not go through a keyhole Deflection success Head-On Impact Deflection of NEAs: A Case Study for Apophis, Planetary Defense Conference 2007, Mar 2007, Wash. DC. See

Overview of deflection concepts “Impulsive” techniques Kinetic impactor Nuclear (stand-off) explosion “Slow-push” (or –pull) techniques Gravity tractor Ion-beam shepherd Mass driver Albedo change Mirror-bee concept Solar shadow Electric solar wind sail 11

Impulsive techniques – Don Quijote Movie at watch?v=h0FTByUifR4 watch?v=h0FTByUifR4 ESA-funded study performed around 2004 by European industry Orbiter and impactor (Hidalgo and Sancho) 12

Impulsive techniques – AIDA ESA-internal study performed in 2012 with APL/USA Impacting the smaller object of a binary asteroid Orbital period will change Can be seen in light curves => Easier to measure! 13 NEA binary 1999 KW4 - Radar derived shape model of the NEA binary 1999 KW4 (Ostro et al., 2006). Pravec et al. (2006)

Impulsive techniques – Nuclear “Stand-off” explosion Radiation pressure of x-ray photons and thermal vaporisation produce push Politically sensitive Studied by TSNIIMASH within the EC-funded NEOShield project ( Studied by some US-based groups (e.g. Los Alamos) 14 Yield of Hiroshima bomb: 15 kt TNT (1 kt TNT = J)

Impulsive techniques – The big issue Effectiveness of momentum transfer is a BIG unknown!  is the momentum transfer efficiency  ranges from 0 to 20 (?) Change in position can be estimated from the following formula (Ahrens and Harris 1994): 15

Some typical numbers: Deep Impact mission: 370 kg impactor 10.2 km/s => target comet about 8 x 5 x 5 km 3 Deflection after half an orbit about 6 m (as computed in Workshop #03) 16

Slow-push/pull techniques Gravity tractor 17

Slow-push/pull techniques Ion-beam shepherd 18

Slow-push/pull techniques Mass driver 19

Slow-push/pull techniques Mirror-bee 20

Slow-push/pull techniques Solar shadowing 21

Slow-push/pull techniques Albedo change 22 u/aemp/index.php?p age=albedo

Slow-push/pull techniques Electric solar wind sail ( EO/Sini_Merikallio.pdf) 23

Slow-push/pull techniques The ultimate solution? 24

Slow-push/pull techniques The ultimate solution? No… see “The graveyard of Alderaan” 25

Overview of deflection concepts and my assessment “Impulsive” techniques Kinetic impactor – feasible – Guidance issues? Nuclear (stand-off) explosion – political issues “Slow-push” (or –pull) techniques Gravity tractor – feasible but difficult Ion-beam shepherd – feasible and interesting Mass driver – science fiction Albedo change – science fiction Mirror-bee concept – science fiction Solar shadow – size of sail? Not quite sci fi? Electric solar wind sail – how to attach? Sci fi 26

In more detail Ion Beam Shepherd for Asteroid Deflection C. Bombardelli, J. Pelaez, arXiv: v1 [physics.space-ph] (2011) 27

In more detail GT = Gravity tractor IBS1 = ‘near-future’ ion thruster IBS2 = ‘state of the art’ thruster From: C. Bombardelli, J. Pelaez, arXiv: v1 [physics.space-ph] (2011) 28

Summary Overview of deflection mission strategies from a technical point of view We learned how to demonstrate a kinetic impactor mission such that the effect could actually be measured We learned some details on the so-called Ion-Beam Shephard (IBS) In workshop: Look at impactor on secondary in 1999 FG3 – how much will the orbital period be changed Is the IBS is feasible? 29

Workshop – task 1 Take the binary asteroid 1996FG3. The distance between the two components is 2.8 km. Assume a circular orbit. What is the orbital period? Assume an asteroid density of 1.4 g/cm 3 and a momentum efficiency of  = 2. Assume that the Deep Impact impactor hits the secondary (370 kg, 10.2 km/s). By how much do you change the period? How can this be measured? 30

Workshop – task 1 - Hint Assume circular orbit – compute velocity ‘before’ from observed period Compute new velocity using conversation of momentum Assume same orbit, compute new period with new velocity. What’s the difference in seconds? To assess whether it is measureable: How many periods are there in one year? What is the accumulated change in period over a year? What does this mean for any observed eclipses between the two objects? 31

Workshop – task 1 - Hint Alternatively: Use the vis-viva theorem to compute the new semi-major axis; then use Kepler’s 3 rd law to compute the change in the period. 32

Workshop – task 1 - Hint Alternatively: Use the vis-viva theorem to compute the new semi-major axis; then use Kepler’s 3 rd law to compute the change in the period. 33

Workshop – task 2 – Ion-Beam Shepherd Let’s assume that we want to use two Smart-1 spacecraft mounted ‘back-to-back’ as Ion-Beam Shepherd. Using the data sheet of the S-1 ion engine (*), where would you put the spacecraft? How much do you shift Apophis after one year/two years/ten years/twenty years? 34 (*) Image credits: ESA

Workshop – task 2 – Hint Assume a distance to the asteroid such that the complete ion beam will impinge the asteroid The thrust of the engine is given (in Newton) From that, compute s = f (t) 35 (*)