High-speed intercept missions, which include kinetic impactors and nuclear penetration devices, may be required to mitigate the threat from a near-Earth object. Various guidance laws, including the pulsed proportional navigation (PPN) guidance and advanced predictive guidance, are examined for the autonomous terminal-phase guidance and control of asteroid interceptors. The asteroid Apophis is used as an illustrative example to show that current technology can be used for high-speed intercept missions. A mission scenario based on a 2-dimensional orbital intercept model is simulated using classical, modified, and predictive guidance laws. Simulations show that intercept is possible even using the simple PPN guidance law for small target asteroids with an acceptable margin of error. The mission scenario is also simulated with a high-fidelity simulation program, called CLEON. The study results verify the applicability of the various guidance laws examined, and also confirm the suitability of the CLEON software for asteroid intercept mission design.

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An intercept mission with nuclear explosives is the only practical mitigation option against the most probable impact threat of near-Earth objects (NEOs) with a short warning time (e.g., much less than 10 years). The existing penetrated subsurface nuclear explosion technology limits the intercept velocity to less than approximately 300 m/s. Consequently, an innovative concept of blending a hypervelocity kinetic impactor with a subsurface nuclear explosion has been developed for optimal penetration, fragmentation, and dispersion of the target NEO. A proposed HAIV (hypervelocity asteroid intercept vehicle) consists of a kinetic-impact leader spacecraft and a follower spacecraft carrying nuclear explosives. This paper describes the conceptual development and design of a baseline HAIV system and its flight validation mission architecture for three mission cost classifications (e.g., $500M, $1B, and $1.5B).