Air Weapons: January 22, 2003

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We reported last October on the potential problem (or non-problem) with jamming GPS signals to disable JDAM smart bombs. This time last year reported on a possible case of Iraq testing GPS jamming against a U.S. air strike by No-Fly Zone patrol aircraft. Now the story going around now is that Iraq had bought hundreds, or thousands of GPS jammers. The JDAM has a backup inertial guidance system, so that if the GPS signal is jammed, the less accurate inertial guidance system takes over. The inertial guidance will land the bomb within 150 feet of the target, GPS will get to within 30 feet. The air force is silent on what, if any, jam-proofing it is doing for it's JDAM bombs. There are several approaches to defeating GPS jamming, and knowing which one JDAM uses makes it easy to develop a way to jam the "jam-proof" GPS. So the air force is understandably reluctant to discuss what they are doing. Given the cost of jam proofing all existing JDAMs, it's more likely that jam-proof JDAMs will only be used against targets where the GPS accuracy is vital. Against most targets, the accuracy provided by the inertial guidance system will do. Also note that you can bomb GPS jammers with a bomb equipped with a guidance system that homes in on a GPS jamming signal. For that reason, it's thought that any use of GPS jammers will involve dozens of jammers in each area so protected.

 

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