Defending Planet Earth

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2011 American Astronautical Society Robert H. Goddard Memorial Symposium--Mike A'Hearn, University of Maryland


<ul><li> 1. Defending Planet Earth<br />Mike AHearn<br /></li></ul> <p> 2. Chixculub<br />31-3-11<br />Goddard Symposium<br />mfa - 2<br />Every 50-100 Myears<br /> 3. Tunguska<br />31-3-11<br />Goddard Symposium<br />mfa - 3<br />Airburst of oblique impactor<br />5-30 Mtons of TNT (20-130 Pj) 30-100m diameter impactor Everything flattened over &gt;2000 km2 Possibly one every 200 years<br />1927 vs. 2008<br /> 4. Size Distribution &amp; Frequency<br />31-3-11<br />Goddard Symposium<br />mfa - 4<br /> 5. Finding Them<br />From Space vs. from Earth<br />Earth-trailing orbit is fastest<br />From Earths surface is cheapest<br />IR vs. Visible<br />IF! In space, IR seems better<br />Goal of G. E. Brown survey<br />90% of &gt;140m<br />31-3-11<br />Goddard Symposium<br />mfa - 5<br /> 6. Kill Curves<br />31-3-11<br />Goddard Symposium<br />mfa - 6<br /> 7. Annual Deaths<br />31-3-11<br />Goddard Symposium<br />mfa - 7<br />LP Comets ignored ~10%, notimportant<br />LP Comets ignored ~50% Whoops!<br /> 8. Mitigation (per NRC)<br />4 approaches depending on circumstances<br />Civil defense (evacuation, sheltering, first aid, etc.<br />Up to 50m diameter?<br />Slow Push-Pull (tug, solar heating, albedo change, gravity tractor, et al.)<br />Needs decades to operate (plus time to build, etc.)<br />Max size 300-600 m diameter<br />Gravity tractor closest to ready and least dependent on properties of NEO<br />Kinetic Impacts (Super Deep Impact)<br />sensitive to porosity of top meters to tens of meters<br />momentum transfer efficiency not known<br />much wider range of applicability (max size 1 to 1.5 km, shorter warning for small ones)<br />Nuclear blast<br />standoff blast best<br />works up to 10 km and relatively short warning<br />31-3-11<br />Goddard Symposium<br />mfa - 8<br /> 9. Mitigation Applicability<br />31-3-11<br />Goddard Symposium<br />mfa - 9<br /> 10. What Next?<br />Don Quixote-like mission<br />a rendezvous spacecraft at a small NEO followed by a large impactor<br />biggest gain in knowledge directly related to mitigation<br />Guess $1.5G; Good for international collaboration<br />Gravity tractor demonstration<br />fewer unknowns other than engineering<br />second priority<br />Apophis a possible target but any small NEO will do<br />Cant predict which might need to be used first<br />Small NEO is by far the most likely<br />Warning time very uncertain but short warnings are likely at ~100m diameter or less<br />31-3-11<br />Goddard Symposium<br />mfa - 10<br /> 11. Research Needs<br />Momentum transfer<br />Warning times<br />Tails of orbital distribution<br />NEO properties - spin &amp; shape, multiplicity, &amp; especially porosity and density<br />lots for science but not so much for hazard mitigation<br />hence radar programs at Arecibo and Goldstone<br />Physics of airbursts<br />search strategy - death plunge vs. full survey<br />Effects of the wide range of NEO properties on the mitigation strategy<br />tsunami generation<br />NEO disruption<br />31-3-11<br />Goddard Symposium<br />mfa - 11<br /> 12. Incomplete Mitigation<br />31-3-11<br />Goddard Symposium<br />mfa - 12<br />Risk of incomplete mitigation could lead to paranoia or even retaliation<br />Risk of retaliation could lead to total inaction<br />Requires official, working level close cooperation<br /> 13. Bottom Line<br />Insurance prevents destruction rather than compensating to rebuild<br />How much insurance do we want?<br />31-3-11<br />Goddard Symposium<br />mfa - 13<br /> 14. Backup Slides<br /></p>