As of this year 31 of the 82 American Aegis equipped ships have anti-missile/satellite capability. If all Aegis ships were converted, the U.S. would have a formidable, and very flexible, capability to defeat ballistic missiles and low flying spy satellites. So the navy is applying pressure to get money to keep the older Aegis ships (the Ticonderoga's and the first few Arleigh Burke class destroyers) in commission for this. This depends on Congress providing enough money for running these ships and to convert them (for about $20 million each) and supply each ship with four or more SM-3 anti-missile missiles (about $10 million each).
The Aegis anti-missile system has had a success rate of over 80 percent in knocking down incoming ballistic missile warheads during test firings. To achieve this, two similar models of the U.S. Navy Standard anti-aircraft missile are in service, in addition to a modified (to track incoming ballistic missiles version) of the Aegis radar system.
The RIM-161A, also known as the Standard Missile 3 (or SM-3), has a range of over 500 kilometers and max altitude of over 160 kilometers. The Standard 3 is based on the anti-missile version of the Standard 2 (SM-2 Block IV). This SM-3 missile has a shorter range than the SM-2, which can destroy a warhead that is more than 200 kilometers up. The SM-3 is only good for anti-missile work, while the SM-2 Block IV can be used against both ballistic missiles and aircraft. The SM-2 Block IV also costs less than half what an SM-3 costs.
The Standard 3 has four stages. The first two stages boost the interceptor out of the atmosphere. The third stage fires twice to boost the interceptor farther beyond the earth's atmosphere. Prior to each motor firing it takes a GPS reading to correct course for approaching the target. The fourth stage is the nine kilogram (20 pound) LEAP kill vehicle, which uses infrared sensors to close on the target and ram it. The Aegis system was designed to operate aboard warships (cruisers and destroyers that have been equipped with the special software that enables the AEGIS radar system to detect and track incoming ballistic missiles). However, there is also a land based version.