Late detection worsens the situation by limiting planning time
Morrison in 2 (David Morrison, NASA Astrobiology Institute; Alan W. Harris, NASA Jet Propulsion Laboratory; Geoffrey Sommer, RAND Corporation; Clark R. Chapman, Southwest Research Institute; Andrea Carusl, Istituto di Astrofisica Spaziale, Rome; Dealing with the Impact Hazard, 2002, http://www.lpi.usra.edu/books/AsteroidsIII/pdf/3043.pdf) DF
It is facile but probably misleading to focus on a sce- nario where an NEO progresses in a step function from zero threat to Earth impactor. The threat that stays a threat will experience an overall rise in impact probability, as the er- ror ellipse shrinks while Earth stays within it. Many more threats than not, however, will suddenly see their impact probability go to zero as the error ellipse shrinks to exclude Earth or shrinks to exclude dangerous keyholes for the case of a resonant return. This feature of the evolution of im- pactor uncertainty will encourage those who wish to defer commitment to interception or who just want to keep the public purse closed. The net effect is that the system reac- tion time will need to be much shorter than the warning time from the point of confirmed threat. This already-chal- lenging situation will only be worsened by failure to ex- amine scenarios and develop appropriate contingency plans. To date the NEO community has not made much effort to pursue such options or enter into dialogue with government organs that deal with security issues. Early detection of asteroids is absolutely critical to deflecting them—scientists’ best deflection strategies require hundreds of years.
The asteroid interception and diversion experts are mostly hobbyists — planetary scientists, astronomers and engineers who think up these strategies on their own time. But the ideas are plentiful: As our gatefold shows, the path from detection to mitigation could include low-thrust engines, solar sails, standoff nuclear explosions and more. Melosh, for example, has been focusing on the use of solar collectors, which could concentrate sunlight on an asteroid, vaporizing enough material to gradually nudge the rock off course. Until recently, this idea amounted to little more than a series of conceptual sketches bolstered by calculations. Then Melosh learned of L'Garde, a California company that makes smaller versions of the exact collectors he needs. With a few adjustments, he says, his strategy could be put to work tomorrow. It would take years for sunlight to redirect an asteroid, however, so advance notice is absolutely critical. Ditto for tactics that would involve painting an incoming asteroid or covering its surface with white glass beads — both approaches would make the asteroid more reflective, increasing the tiny reaction forces produced when sunlight is radiated back into space. Over several centuries, the cumulative effect of these slight forces would alter the asteroid's velocity and cause a miss. "You let the Sun do the work," says Jon Giorgini of NASA's Jet Propulsion Laboratory (JPL), one of the scientists who projected 1950DA's orbit out to 2880. "The key," says Donald Yeomans, who heads the NEO Program Office at JPL, "is you've got to find them early. If they're on an approach trajectory and you've [only] got a few months, there's not much you can do." Given ample time, an effective defense strategy might require that a probe be launched to study the structure of the incoming body. Not all asteroids are the solid objects familiar from museum meteorite displays. Some are porous, others are collections of rubble loosely held together by gravity. Exploding a nuclear bomb nearby might nudge a dense asteroid off track, but it could break a brittle one into pieces, effectively multiplying the threat by creating smaller but still lethal rocks. Each threat, in other words, requires an adjustment of strategy. "You need to find out [the asteroid's] density, find out its mass, its porosity, its composition, because all these things are important if you want to effect some kind of mitigation or deflection," says Yeomans.
Early Detection key
It is possible to deflect asteroids, but we MUST detect them at least 30 years in advance.
Also possible is a dock-and-push approach, in which a spacecraft parks on the asteroid's surface, fires its thrusters, and alters the trajectory. Robert Gold of the Applied Physics Laboratory at Johns Hopkins University says the probe he designed for NASA's Near Earth Asteroid Rendezvous mission — the first to land on an asteroid — could divert a hundred-meter-wide object, which is large enough to wipe out the Washington Beltway. "If you found [the asteroid] 30 years in advance, that little 6-foot by 6-foot spacecraft could provide enough impulse to make it miss Earth," he says. Still, as Yeomans warns, none of this will work without advance notice. Currently, NASA expects to find only about 90 percent of the NEOs large enough to cause global catastrophes. The remaining 10 percent are too dark for today's telescopes, or too difficult to distinguish from the many asteroids that orbit harmlessly in the solar system's main asteroid belt between Mars and Jupiter. Andrea Milani, of the Space Mechanics group at the University of Pisa in Italy, wants to find the hidden large NEOs and extend the survey down to objects as small as 300 meters across. Both goals require a new generation of ground-based telescopes capable of detecting fainter objects, and possibly space-based observatories to peer into obscure areas of the solar system. The ground-based, 8.4-meter Large-aperture Synoptic Survey Telescope is one possibility, but its $120 million price is the equivalent of 40 years of the current search budget.
Adequate warning is key to develop the necessary combination of mitigation strategies
IRWIN I. SHAPIRO et al in 10,( Harvard-Smithsonian Center for Astrophysics, Chair FAITH VILAS, MMT Observatory at Mt. Hopkins, Arizona, Vice Chair MICHAEL A’HEARN, University of Maryland, College Park, Vice Chair ANDREW F. CHENG, Johns Hopkins University Applied Physics Laboratory FRANK CULBERTSON, JR., Orbital Sciences Corporation DAVID C. JEWITT, University of California, Los Angeles STEPHEN MACKWELL, Lunar and Planetary Institute H. JAY MELOSH, Purdue University JOSEPH H. ROTHENBERG, Universal Space Network, Committee to Review Near-Earth Object Surveys and Hazard Mitigation Strategies Space Studies Board Aeronautics and Space Engineering Board Division on Engineering and Physical Sciences, THE NATIONAL ACADEMIES PRESS, http://www.fas.harvard.edu/~planets/sstewart/reprints/other/4_NEOReportDefending%20Planet%20Earth%20Prepub%202010.pdf)\
Realistic mitigation is likely to include more than one technique if for no other reason than to provide confidence.In any case of mitigation, civil defense will undoubtedly be a component whether as the primary response or as the ultimate backup. Finding: No single approach to mitigation is appropriate and adequate to fully prevent the effects of the full range of potential impactors, although civil defense is an appropriate component of mitigation in all cases. With adequate warning, a suite of four types of mitigation is adequate to mitigate the threat from nearly all NEOs except the most energetic ones.