Rocket motor mystery continues to halt AMRAAM deliveries

Raytheon Missile Systems has not delivered an AIM-120 Advanced Medium-Range Air-to-Air Missile (AMRAAM) in nearly two years because of an unexplained flaw in the missile's solid rocket motor.

The motors, supplied by ATK, have suffered mass failures when subjected to routine cold temperature tests. The issue has surprised and baffled ATK and Raytheon because the formulation and materials used to produce the rocket propellant fill have not changed – and have been in production, without incident, for more than 30 years. However, by late 2009 reliability problems had emerged with the ATK motors and now Raytheon says it has a stock of around 800 missiles that cannot be delivered. The US Depertment of Defense (DoD) has suspended payments to Raytheon until the rocket issues are solved and Raytheon admits that a final, reliable solution has yet to be found.

ATK's motors are failing a specific 'cold soak' test where the rockets are frozen to -65 degrees F (-54 degrees C) and then fired to prove they remain functional after carriage at high altitudes. ATK supplies motors in batches of 48 and the US practice is to test nine random examples from each batch.

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