Air Defense: Aegis Defeats IRBMs


April 22, 2011: The U.S. Navy has successfully tested its Aegis anti-missile system against an IRBM (Intermediate Range Ballistic Missile), similar to those used by Iran. The IRBM was launched from Kwajalein Atoll (in the Marshall Islands) towards a patch of ocean off the Hawaiian Island, 3,700 kilometers distant. Within eleven minutes of the IRBM lifted off, a long range X-Band radar on Wake Island (north of Hawaii) spotted the incoming missile, passed the data to a U.S. destroyer off Hawaii, which calculated the flight path of the target and launched a SM-3 Block 1A missile, which destroyed the IRBM. This was a test of the land based Aegis system that will be built in Europe to protect against hostile IRBMs.

This was first test of an Aegis software upgrade (3.6.1) that enables Aegis to track and intercept IRBMs (ballistic missiles with a range of 3,000-5,500 kilometers). This was the 21st successful test of Aegis, which now has an 84 percent success rate in tests. There are other upgrades in the works. The next one is SM-3 Block 1B (mostly improvements in the final stage, or warhead capabilities).

At the moment, Aegis anti-missile systems are hot. The U.S. government, encouraged by the high success rate of Aegis SM-3 missiles fired at incoming ballistic missiles, has been expanding the number of SM-3 equipped ships. With 18 Aegis anti-missile equipped ships in service now, there are plans to have more than twice as many in the next few years.

Converting Aegis ships to fire anti-missile missiles 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 missiles, an Aegis equipped ship 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. This means 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 basic anti-missile missile RIM-161A, also known as the Standard Missile 3 (or SM-3). It has a range of over 500 kilometers and max altitude of over 200 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 ten times higher. 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). There is also a land based version that Israel is interested in buying, and is basically the same one that would be installed in Europe.



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