June 18, 2013: Recently the United States successfully tested the new PAC-3 MSE version of the Patriot anti-missile missile. The new rocket motor and other new or redesigned components boost the PAC-3s range to over 35 kilometers and altitude to over 36,000 meters (112,000 feet, nearly 50 percent more than earlier PAC-3s). The PAC-3 MSE is heavier than previous PAC-3s, and this will reduce the number that can be carried on a launcher from 16 to 12.

Introduced in 1981, the Patriot originally had a shelf life of 15 years but several rounds of upgrades and refurbishments enable many of the 100,000 missiles built since the 1980s to be kept in service for another decade or more. The refurbishment also includes using new technology to accurately measure age-related decay in many components. This is an important aspect of being able to extend shelf-life in missiles and aircraft. This refurbishment is how many missiles built over two decades ago turned into MSE versions.

The current version of the original Patriot missile design (MIM-104E PAC 2) cost $2 million each and can be used against aircraft and some missiles. The smaller PAC-3 (MIM-104F) anti-missile missile can only be used against missiles and can cost up to $3 million each. PAC-3 entered service in 2002.

The U.S. Army has ten Patriot anti-aircraft missile battalions. Each battalion has 12-24 launchers (in 3-6 batteries). Each battery is manned by about a hundred troops and contains a radar, plus four launchers. A battery can fire either of the Patriot missile types. The PAC-3 missile is smaller than the anti-aircraft version (PAC-2), thus a Patriot launcher can hold 12 or 16 PAC 3 missiles, versus four PAC-2s. A PAC 2 missile weighs about a ton, an original PAC-3 weighed about a third of that. The PAC-3 has a shorter range (originally about 20 kilometers) versus 70 kilometers for the anti-aircraft version. There is also an anti-missile version of the PAC-2, but it is less effective than the PAC-3 but gives Patriot batteries the ability to be able to quickly deal with enemy aircraft or missiles.

While each Patriot launcher, loaded with PAC-3 missiles, can only defend against ballistic missiles approaching within its shorter range (20-35 kilometers), the Patriot radar can detect targets out to a hundred kilometers. Two PAC-3 missiles are fired at each incoming ballistic missile, to increase the probability of a hit. The PAC-3 missile has its own radar and uses it to track the incoming warhead and execute a collision course.