Air Weapons: Missiles Suddenly Can't Handle The Cold

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July 25, 2012: The U.S. Air Force has another mystery on its hands. The first one is why the F-22 air supply is making it difficult for some pilots to stay conscious. The second problem, which is actually almost as old, is all about defective rocket motors for AIM-120 AMRAAM air-to-air missiles. As a result of the rocket problem no missiles have been delivered for nearly two years. The delays have been due to faulty solid fuel rocket motors, which was discovered during testing that the air force performs on a few of every new batch of missiles. The problem is that when rocket motors are exposed to very cold conditions (as would happen when an aircraft is flying at a high altitude) they become unreliable. The air force is withholding over half a billion dollars in payments until the reliability problem is fixed. At the same time the manufacturer is frantically trying to discover the cause of the failures. The manufacturer insists that it is building the rocket motors the same way it has for three decades. So far it is a mystery as baffling as the one with the F-22 air supply.

AMRAAM has been around for a while and undergone several upgrades, without problems appearing in components that are often built the same way they have been for decades. But there have been many changes to components, including lots of new stuff. Thus it's likely that some of the components of the solid fuel (a slow burning explosive) rocket have changed and chemists are scrambling to find out what it is.

AMRAAM entered service in 1992, more than 30 years after the first radar guided air-to-air missile (the AIM-7 Sparrow) appeared. AMRAAM was designed to fix all the reliability and ease-of-use problems that cursed the AIM-7. But AMRAAM has had only had a few opportunities to be used in combat, and over half of those launched have hit something. The AIM-120D version entered service five years ago, has longer range, greater accuracy, and resistance to countermeasures. So far, AMRAAMs have spent nearly 2 million hours hanging from the wings of jet fighters in flight. Some 2,400 AMRAAMs have been fired, mostly in training or testing operations. That’s about a quarter of those produced.

AMRAAM weighs 172 kg (335 pounds), is 3.7 meters (12 feet) long, and 178mm (7 inches) in diameter. AMRAAM has a max range of 70 kilometers. These missiles cost about a million dollars each. They are complex mechanical, electronic, and chemical systems and each of them, on average, suffers a component failure every 1,500 hours.

The air force and the navy have had an increasing number of incidents where their suppliers of high-tech weapons and equipment screwed up. Cancelling orders and taking manufacturers to court has not eliminated the problems. The military accuses the manufacturers of having a bad attitude, feeling that if there are problems it's easier to cozy up to members of Congress than it is to fix the technical problems. So far, that seems to be working, while the weapons and equipment don't.

 


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