February 27, 2013: The U.S. Navy recently tested its Aegis anti-missile system using a STSS (Space Tracking and Surveillance System) to spot a medium-range (1,000-3,000 kilometers) ballistic missile and guide the SM-3A missile warhead to the point where the warhead guidance system could take over and score a hit.

The United States put a pair of experimental STSS (Space Tracking and Surveillance System) satellites into orbit four years ago. These have better heat sensors and are there to provide earlier warning of ballistic missile launches, so that anti-missiles can hit ballistic missiles earlier and with a higher probability of destroying them. STSS can also track other satellites, making it easier to destroy enemy satellites in wartime. STSS recently demonstrated an ability to detect short range, air-launched missiles. This latest test proved that STSS could work with Aegis equipped ships to shoot, spot, and knock down Iranian, North Korean, and Chinese missiles, especially the new “carrier killer” ballistic missiles China has developed. The air force wants to put a network of STSS birds up there, so all potential trouble spots can be constantly monitored for ballistic missile launches.

Because of this recent success, Aegis anti-missile systems are much in demand. The U.S. government, encouraged by the high success rate (80 percent of 30 tests) of Aegis SM-3 missile tests, has been expanding the number of SM-3 equipped ships. With 18 Aegis anti-missile equipped ships in service now and plans to have more than twice as many in the next few years.

Converting an Aegis ship to fire anti-missile missiles costs about $15 million (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.

SM-3 is also known as the RIM-161A. It 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 version turned out to be effective against shorter range ballistic missiles. 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 of 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 9 kg (20 pound) LEAP kill vehicle, which uses infrared sensors to close on the target and ram it.