Post on 22-Jan-2016
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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)
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: ESA
News
Workshop on 2011 AG5 took place at Goddard Space Flight Center on 29 May 2012
• 2011 AG5 is highest on risk list – 1:500. But: low confidence
• No need to act now. Observations in 2013 will be timely enough
A 2nd 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 2012
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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
Asteroid does not hit Earth (miss distance is n * Rearth where n is still tbd)
Asteroid does not go through a keyhole
Deflection success
Head-On Impact Deflection of NEAs: A Case Study for 99942 Apophis, Planetary Defense Conference 2007, 05-08 Mar 2007, Wash. DC. See http://www.doom2036.com/P2-3--Dachwald.pdf
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
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Impulsive techniques – Don Quijote
Movie at http://www.youtube.com/watch?v=h0FTByUifR4
ESA-funded study performed around 2004 by European industry
Orbiter and impactor (Hidalgo and Sancho)
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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!
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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 (http://new.tsniimash.ru/)
Studied by some US-based groups (e.g. Los Alamos)
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Yield of Hiroshima bomb: 15 kt TNT(1 kt TNT = 4.2 1012 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):
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Some typical numbers:
Deep Impact mission: 370 kg impactor10.2 km/s => target comet about 8 x 5 x 5 km3
• Deflection after half an orbit about 6 m (as computed in Workshop #03)
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Slow-push/pull techniques
Albedo change
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http://aeweb.tamu.edu/aemp/index.php?page=albedo
Slow-push/pull techniques
Electric solar wind sail (http://spacegeneration.org/images/stories/Projects/NEO/Sini_Merikallio.pdf)
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Slow-push/pull techniques
The ultimate solution?• No… see “The graveyard of Alderaan”
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Overview of deflection conceptsand 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
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In more detail
Ion Beam Shepherd for Asteroid Deflection• C. Bombardelli, J. Pelaez, arXiv:1102.1276v1 [physics.space-ph] (2011)
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In more detail
GT = Gravity tractor
IBS1 = ‘near-future’ ion thruster
IBS2 = ‘state of the art’ thruster• From: C. Bombardelli, J. Pelaez, arXiv:1102.1276v1 [physics.space-ph] (2011)
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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?
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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 of1.4 g/cm3 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?
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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?
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Workshop – task 1 - Hint
Alternatively: Use the vis-viva theorem to compute the new semi-major axis; then use Kepler’s 3rd law to compute the change in the period.
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Workshop – task 1 - Hint
Alternatively: Use the vis-viva theorem to compute the new semi-major axis; then use Kepler’s 3rd law to compute the change in the period.
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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(*) http://www.snecma.com/IMG/files/fiche_pps1350g_ang_2011_modulvoir_file_fr.pdf
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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(*) http://www.snecma.com/IMG/files/fiche_pps1350g_ang_2011_modulvoir_file_fr.pdf