| Abstrakt: |
Asteroidal impact threats to the Earth may be predicted a century or more in advance. Several methods of mitigating these threats have been proposed. Here I evaluate changing an asteroid's albedo to change the Solar radiation pressure force, and hence its orbit. Albedo may be increased to near-unity by applying a thin ( ∼ 0.1 μ m) reflective coat of alkali metal, dispensed as vapor by an orbiting spacecraft. A complete coat reduces the effective Solar gravity, changing the orbital period and displacing the asteroid by a distance proportional to elapsed time. A Tunguska-class (50 m diameter) asteroid in a nominal orbit with perihelion 1 AU and aphelion 3 AU ( a = 2 AU, e = 0.5 ) may be displaced along its path by ∼ 1000 km in 100 years, sufficient to avoid impact in a populated area, by application of one kg of lithium or sodium metal over its entire surface. Alternatively, coating one hemisphere of an asteroid in an elliptical orbit may produce a Solar radiation torque on its orbit, related to but distinct from the Yarkovsky effect, displacing it by an Earth radius in ∼ 200 years. The acceleration is inversely proportional to the asteroid's diameter and its displacement increases quadratically with time, so the time required for deflection scales as the square root of the diameter (the 1/6 power of its mass). Larger asteroids are difficult to deflect by other means, but deposition of 400 kg of alkali metal makes it possible to prevent the catastrophic impact with the Earth of a km-sized asteroid 200 years in the future. [ABSTRACT FROM AUTHOR] |
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