Asteroids Aff


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Solar evaporation solves NEO deflection

Safaeinili and Ostro 2002 - Jet Propulsion Laboratory, California Institute of Technology (October 24, Ali and Steven J., “ Imaging the Interiors of Near-Earth Objects with Radio Reflection Tomography ” NASA Workshop on Scientific Requirements for Mitigation of Hazardous Comets and Asteroids, pg. 86)

Introduction: In my review of various non-nuclear techniques that might be used to deflect a NEO on a collision course with Earth, the most promising method is one that. was studied by H.J. Melosh et al * . This method uses a solar collector to focus the Sun’s rays on the NEO’s surface where evaporation of the surface caused by heat creates a thrust which modifies the NEO’s trajectory over a period of time. Such a technique has a huge advantage because it neither requires stabilizing the NEO nor landing on it. As the NEO rotates under the illuminated spot, fresh material is brought into the heated area so evaporation is continuous. Furthermore it does not, for the most part, depend on the composition of the NEO. It can evaporate stony or icy bodies but probably not iron NEOs. Fortunately these are rare. The steady push generated by solar evaporation minimizes the danger of disrupting the NEO in contrast to an impulse. There are quite a few technical hurdles to overcome in maturing this technique, but none seem improbable or anymore difficult than other methods.


Nuclear explosions work

Lewis 1996 - professor of planetary science at the University of Arizona's Lunar and Planetary Laboratory (John S., Rain of Iron and Ice, p. 183-222)

There are many methods available for making such small changes in the velocity of an asteroid. One of the favorite techniques proposed by military experts is to explode a small nuclear warhead well clear of the surface of the asteroid, perhaps two asteroid radii from the surface. But simply launching an existing ICBM at the asteroid would not work: such vehicles cannot achieve escape velocity to reach an asteroid on its orbit around the Sun. Further, missile guidance systems are designed to operate for the half-hour of an intercontinental trip, not the weeks or months required for the trip to an asteroid. The mission would have to be accomplished by a military warhead combined with a NASA planetary spacecraft bus that provides guidance and power. The spacecraft need not be massive; the nuclear explosive weighs in at only about 100 kilograms, of which only about 6 kg of bomb vapor strikes the asteroid. The shock wave from the blast is completely negligible, but the enormous thermal energy of the explosion heats a thin surface layer over the entire face of the asteroid visible to the warhead to high enough temperatures to vaporize that surface layer. The vapor departs at about 4 kilometers per second, imparting a brief impulse to the asteroid. By the nature of this technique, the force it imparts to the asteroid is very evenly distributed. Supposing that a layer 0.03 cm thick with a density of 3 grams per cubic centimeter is vaporized and departs at 4 kin/s, the recoil momentum imparted to the asteroid is sufficient to change the asteroid's velocity by 10 centimeters per second. The fifty metric tons of surface material removed is more than adequate to deflect the 20 million metric tons of asteroid by the small amount required to assure a generous safety margin when it flies by Karth. The explosion of a nuclear warhead with a yield of tens of kiloions in space far from Earth guarantees that a two-gigaton explosion does not take place on Earth. The expense of the hardware and mission operations should be around $200 million (perhaps as much as $1 billion if only one such device were built and no production-line efficiencies could be realized). Readers concerned about the environmental impact of such an explosion should realize that the asteroid would not be contaminated to any significant degree by radioactive bomb debris, since the surface layer would be boiled off by the blast. The bomb vapor would be swept out of the solar system by the solar wind at a speed of about six hundred kilometers per second. A month after the explosion the weapon debris would be 11 AU from the Sun, beyond the orbit of Saturn, and so diluted by the solar wind that it would be virtually indetectable. The one gram of matter converted to energy by the nuclear explosion would quickly get lost amid the 4 million metric tons of light given off each second by the Sun. The net result of the asteroid deflection is really a twofold benefit to Earth: a devastating impact would be avoided, and there would be one less nuclear warhead on Earth.
Nuclear weapons are comparatively the best strategy

NASA Report to Congress 7 (March, “Near-Earth Object Survey and Deflection Analysis of Alternatives”,

The study team assessed a series of approaches that could be used to divert a NEO potentially on a collision course with Earth. Nuclear explosives, as well as non-nuclear options, were assessed. Nuclear standoff explosions are assessed to be 10-100 times more effective than the non-nuclear alternatives analyzed in this study. Other techniques involving the surface or subsurface use of nuclear explosives may be more efficient, but they run an increased risk of fracturing the target NEO. They also carry higher development and operations risks. Non-nuclear kinetic impactors are the most mature approach and could be used in some deflection/mitigation scenarios, especially for NEOs that consist of a single small, solid body. "Slow push" mitigation techniques are the most expensive, have the lowest level of technical readiness, and their ability to both travel to and divert a threatening NEO would be limited unless mission durations of many years to decades are possible. 30-80 percent of potentially hazardous NEOs are in orbits that are beyond the capability of current or planned launch systems. Therefore, planetary gravity assist swing by trajectories or on-orbit assembly of modular propulsion systems may be needed to augment launch vehicle performance, if these objects need to be deflected.

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