The Giggle Factor (GF). Mention "Planetary Defense" and you'll soon understand. Even without invoking the sinister vision of alien beings arriving to enslave or destroy humanity, the eyebrows of serious and senior members of the national defense and scientific communities go askew when the subject is broached, whether at cocktail parties or congressional budget hearings. Even the most ardent supporters of defending the Earth from cataclysmic cometary or asteroidal impacts share occasional public or private chuckles with colleagues and skeptics-behavior considered unthinkable when discussing means to avert or mitigate the catastrophic epidemics, wars of aggression and genocide, and terrestrial natural disasters that have peppered man's history on Earth.