The Heritage Foundation’s Defending America, A Plan to Meet the Urgent Missile Threat advocates a combined sea-based and space-based NMD system. The initial sea-based system, described below, would use 650 Navy Theater Wide (NTW) Block II missiles on all 22 existing Aegis cruisers. These would be supported by a constellation of Space-Based Infrared (SBIRS-Low) satellites for launch detection, target tracking and engagement control. The system would attempt to intercept warheads during the exoatmospheric midcourse portion of their flight.
The NTW Block II missile is in the research stage. It is designed for midcourse intercept of theater missiles. It has a proposed maximum speed of 4.5 km/s, and thus a footprint of roughly 1000 km. Any higher speed would result in the system being classified as a National Missile Defense under US-Russian agreements distinguishing TMD from NMD. Its kill vehicle, the Lightweight Exoatmospheric Projectile (LEAP), uses cooled infrared seekers.
The Navy’s Aegis cruisers have phased-array SPY-1D radars for target-acquisition. These radars are optimized for air defense; adaptation for ICBM tracking would involve reworking their 12 million lines of computer code. Resolution sufficient for discrimination between warheads and decoys could not be obtained without a complete redesign of the physical system.
Aegis ships are equipped with vertical-launch systems (VLS). Each cruiser has 122 21-inch diameter vertical-launch cells which currently contain missiles for anti-air, anti-sub, and anti-ship services. These systems are currently being retrofitted for and tested with lower-tier theater missile defense systems.
SBIRS-Low is a constellation of infrared satellites currently intended for use with the ground-based NMD system. In this sea-based system, it would participate in target tracking and discrimination. It would also supplement the ship-based radars to provide early trajectory estimates.
There are several potential technical problems with this proposed system. Most importantly, as a midcourse system, it would be susceptible to the same easy-to-achieve countermeasures that would plague the currently proposed
ground-based system. In fact, it would be even more limited it that its SPY-1D radars are not
nearly as competent in target discrimination as the Michael Levi