However, the act of a madman would be the easiest action to prevent. The long experience of the United States military with the command and control of nuclear forces would be highly relevant here, especially since nuclear weapons would have to be used to deflect an asteroid. Command and control could be highly centralized, because there would presumably be more than adequate warning time, and there would be no enemy attacking the command and control system. These countries are highly unlikely to start an aggressive war, least of all by means of asteroid collision. A system built and operated by the US, Japan, and Western Europe is unlikely to be hijacked by any single one of these nations, and it is hard to believe that all of them would agree to deflect an asteroid towards some other country.
Asteroids are inherently unwieldy.
Pardon me for interjecting, but it is clearly inevitable that in the LONG run the planetary defense effort must lie within Defense Dept regi due to the nuclear issue involved. The result indicates that in order to estimate the required explosion energy, a better understanding of cratering under gravity much weaker than on the Earth would be required. Although bright lines of nitrogen and oxygen lie in the near-infrared, there are bright visible nitrogen bands. I agree that such meteoroids may exist and may be more abundant in fresh cometary ejecta. The more reason to do a careful faint meteor spectroscopy during the forthcoming Leonid outburst.