In November 2020 a U.S. Navy destroyer used a SM-3 Block IIA anti-missile missile to intercept an air-launched ICBM type target over the Pacific. This new version of the SM-3 anti-missile missile was developed jointly by the U.S. and Japan. For nearly a decade the U.S. Aegis developer has been working with Japanese firms to develop technology for Aegis to detect and intercept IRBM and then ICBM warheads. What makes ICBM warheads more difficult to intercept is that theyare released from the last stage of the missiles higher up before plunging earthwards towards their targets. The higher up a ballistic missile travels the faster its warhead goes on the way down. The Japanese believed it was possible to adjust the Aegis software to detect these faster warheads and use an improved SM-3 final stage that could detect and intercept that faster incoming target. The November test proved that all this worked.
This continues a decades long trend for improving the effectiveness of the SM-3 anti-missile capabilities. For example, in 2011 there was a successful test of Aegis against an IRBM (Intermediate Range Ballistic Missile) type warhead. Within eleven minutes of the IRBM lift 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 warhead. This was a test to demonstrate that the land-based Aegis systems being built in Europe could protect against hostile IRBMs from Iran or Russia.
The 2011 success was also the 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 currently test has a success rate of over 85 percent. The success of the anti-ICBM capabilities will be followed by other upgrades that are underway. The next one is SM-3 Block 1B, which is mostly improvements in the final stage (warhead) capabilities. The SM-Block 2 was already in development with a faster SM-3 missile and improved terminal guidance for the final stage, that actually intercepts the warhead.
At the moment, Aegis anti-missile systems are very popular. 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 33 Aegis anti-missile equipped ships in service now, there are plans to keep increasing that number, which will include more ships of allies like Japan and South Korea.
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.
There is growing demand for using 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 is the 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 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 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 9 kg (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 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 several countries are interested in buying.
The U.S. does not use ICBMs to provide targets for missile-defense tests but a cheaper substitute produced by Coleman Aerospace. These special target missiles are dropped from an aircraft, and fly to a high altitude and release a warhead that plunges earthward just like a real ICBM warhead. Coleman target missiles that are rolled out the back of a C-17 transport. Coleman has been at this since 1999, often using retired rocket motors from Minuteman missiles for their air launched target systems. Coleman keeps getting business because the only competing systems are foreign and the Department of Defense has a very difficult time buying foreign weapons or military equipment, even if that stuff is cheaper and/or better.
There are some cheaper and better competitors out there. For example, an Israeli firm is offering its own line of “Sparrow” ballistic missile targets. These targets are missiles carried to a high altitude by an F-16, F-15 or a large transport aircraft. When launched, the missiles fly higher and then plunge earthward at a speed and trajectory nearly identical to that of a ballistic missile. This provides an effective target for testing anti-missile systems. All these Sparrow systems are basically air-to-surface missiles equipped to carry electronics reporting all flight characteristics, as well as some explosives so that the missile can be quickly destroyed in the air if it has problems and heads for a populated area. Sparrow is cheaper than the Coleman one that uses components of an actual ballistic missile for their air-dropped test missile systems.
All three models of Sparrow are about eight meters (twenty-six feet) long and look like large missiles with a reentry type warhead that has the shape of an object designed to survive the heat from a high-speed plunge back to earth. That is simulated by using the rocket to using a rocket to accelerate the warhead as it heads down. To a radar that speed makes it look like a ballistic missile warhead reentering the atmosphere. These warheads come in at different speeds depending on the range of the missile. Longer range missiles have a higher re-entry speed and that higher speed makes the warhead harder to track and hit with an anti-missile missile.
The first of the three different models of the Sparrow system appeared in the 1990s to help test the new Arrow anti-missile system. That 1.4-ton Black Sparrow simulated earlier models of the Russian SCUD short range (about three-hundred kilometers) ballistic missile. The 1.8-ton Blue Sparrow simulates later, longer range (up to a thousand kilometers) models of the SCUD type missiles. The 3.2-ton Silver Sparrow simulates a ballistic missile with a range of up to two-thousand kilometers (like the Iranian Shahab 3). A larger Sparrow type missile could deliver an incoming target warhead travelling at ICBM speeds.
Sometimes these target systems can cause problems all by themselves. In September 2013 two Sparrows were used over the Mediterranean for an Arrow test. A Russian electronic monitoring and radar tracking ship (a “spy ship”) was off the Syrian coast to keep an eye on NATO warships in the area and spotted the Sparrows. The Russians reported the use of ballistic missiles and the Israelis quickly revealed that these were Sparrows, not ballistic missiles. This has never been a problem for the Coleman air-launched target warheads, which are launched over the Pacific so that the American Ballistic Missile Defense Test Site on the Kwajalein Atoll can monitor the test. The U.S. has not asked Israel for an ICBM grade Sparrow because there is political opposition to depending on a foreign supplier for this sort of thing.