The U.S. government, encouraged by the high success rate (83 percent) of U.S. Navy Aegis equipped ships using SM-3 missiles to shoot down ballistic missiles, has decided to expand the number of SM-3 equipped ships. Just this year, the navy completed equipping 18 ships with the Aegis anti-missile system, and that number may soon more than triple.
This is part of a larger trend. Last year, the navy cancelled its expensive new DDG-1000 class of destroyers, partly because these ships were built to support amphibious and coastal operations, and did not have a radar that could easily be converted to use SM-3 anti-missile missiles. The DDG-1000 also cost 2-3 times more than Aegis destroyers. With missile defense seen as a higher priority than providing new amphibious and coastal combat capability, the DDG-1000 was killed, and the money saved could be used to build more Aegis destroyers, and convert more current destroyers and cruisers to use SM-3.
With that in mind, the navy is already converting three more Aegis ships to fire anti-missile missiles. This costs about $12 million a ship, mainly for new software and a few new hardware items. This is seen as a safe investment. To knock down ballistic missile, Aegis uses two similar models of the U.S. Navy Standard anti-aircraft missile, in addition to a modified version of the Aegis radar system, tweaked to also track incoming ballistic missiles.
Now the government wants to use Aegis more aggressively to block Iranian or North Korean ballistic missiles, and is proposing that nearly all (over 60) ships equipped with Aegis radar systems, be converted to fire SM-3 anti-missile missiles. This would mean buying over a thousand SM-3 missiles. These currently cost about $10 million each, and the next upgrade (which will deliver more accuracy and reliability) will raise that to $15 million each. While the expanded Aegis program will cost about $20 billion, it's seen as the cheapest way to provide reliable anti-missile defense against Iran and North Korea.
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 turned out to be effective against ballistic missile warheads that are closer to their target. One test saw a SM-2 Block IV missile destroy a warhead that was only 19 kilometers up. An SM-3 missile 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 SM-3 has four stages. The first two 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 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 that Israel is interested in buying.