They have more stringent detection requirements and require more rapid response. They could require search times measured in days and interceptors maintained in readiness, both of which favor space basing of key elements. For most objects, kinetic energy pulverization is the preferred means of deflection. While it would be difficult to perform experiments on the Earth, asteroids frequently pass on accessible trajectories that are suitable for interaction tests. Soft and hard landings, seismic strength tests, pulverization, and deflection tests could provide much of the data needed for kinetic deflection as well as others.
Separate efforts are appropriate for the various sizes of objects.
For large NEOs, ground-based search with large CCD focal planes on existing telescopes is appropriate. Hardware costs would largely be for CCD arrays, which already exist. In would be appropriate to study deflection, particularly kinetic pulverization, to better define the requirements for negation. Further theoretical work would be useful, but experiments are needed that cannot be performed on Earth. They could be performed on asteroids that pass the Earth.