INTERCEPTION OF COMETS AND ASTEROIDS ON COLLISION COURSE WITH EARTH

I delineate the utility, performance, and range of applicability of rocket interceptors designed to disrupt (deflect or pulverize) comets or asteroids on collision course with Earth. I discuss the relationship among several quantities of practical interest in the interception problem, the most important of which are 1) the mass in orbit or initial mass of the interceptor, which will usually dominate the cost of the system, and 2) the blowoff fraction, the fraction of the assailant object's mass expelled to impart transverse momentum, which also provides a measure of the probability that the object will fracture. I calculate optimum interception strategies for both kinetic-energy deflection and nuclear-explosive deflection, assuming a fairly general relationship between the energy deposited and the blowoff mass. In the nuclear-explosive case, I calculate the interceptor mass and cratering effect for detonations above and below the surface as well as directly on the surface of the assailant. Because different assailants could possess a wide range of densities and material properties, the principal value of this work is to show the relationships among the salient parameters.