  Laser ablation of a Near-Earth Object (NEO) on a collision course with Earth
produces a cloud of ejecta which exerts a thrust on the NEO, deflecting it from
its original trajectory. Ablation may be performed from afar by illuminating an
Earth-targeting asteroid or comet with a stand-off "DE- STAR" system consisting
of a large phased-array laser in Earth orbit. Alternatively, a much smaller
stand-on "DE-STARLITE" system may travel alongside the target, slowly
deflecting it from nearby over a long period. This paper presents orbital
simulations comparing the effectiveness of both systems across a range of laser
and NEO parameters. Simulated parameters include magnitude, duration and, for
the stand-on system, direction of the thrust, as well as the type, size and
orbital characteristics of the target NEO. These simulations indicate that
deflection distance is approximately proportional to the magnitude of thrust
and to the square of the duration of ablation, and is inversely proportional to
the mass. Furthermore, deflection distance shows strong dependence on thrust
direction with the optimal direction of thrust varying with the duration of
laser activity. As one example, consider a typical 325 m asteroid: beginning 15
yr in advance, just 2 N of thrust from a ~20 kW stand-on DE-STARLITE system is
sufficient to deflect the asteroid by 2 R_e. Numerous scenarios are discussed
as is a practical implementation of such a system consistent with current
launch vehicle capabilities.
