Only the GMD system missiles are capable of shooting down an ICBM like one fired over a ground distance of 4,600 miles (from Pyongyang to Honolulu)— far into space then down to its target. AEGIS, THAAD, and Patriot ar not currently capable of doing that. AEGIS and THAAD are designed for shorter range and closer approach of the missile when it is struck. AEGIS and THAAD have been tested to fire at ICBM range missiles and there is talk of modifying those missiles to be effective at ICBM range in the future— or until we develop a better substitute.  They would also require the electronic monitorinng and communication with the GMD system to coordinate firing and deal with a coordinated attack.