The success of the U.S. Navy's Aegis system in destroying ballistic missiles, and low orbit satellites, is likely to keep some of the older Aegis equipped ships in commission longer. The first Aegis ships were the Ticonderoga class of cruisers, which entered service in 1983. The 27th, and last one, joined the fleet in 1994. Five have since been retired and four additional ones scheduled for retirement next year have had that postponed. This was mostly due to Congress insisting that not so many of the Ticonderogas be taken out of service. This was because of political pressure to maintain the size of the fleet. None of the four Ticonderogas scheduled for retirement were equipped for anti-missile work. But five of the Ticonderogas in service are and more are scheduled to be converted. Another 21 Burke class destroyers are also equipped for anti-missile work.
As of this year 26 of the 82 American Aegis equipped ships will 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 (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 used, in addition to a modified version of the Aegis radar system, which can now track incoming ballistic missiles.
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-2 missile has a shorter range than the SM-3, which can destroy a warhead that is more than 200 kilometers up. But 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.