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  • Tale of RQ-170 Hijack In Doubt as Told in Tehran
    Posted by David A. Fulghum 7:48 PM on Dec 16, 2011

    Purported Iranian engineering specialists have been taking liberties with the laws of physics in their descriptions of an electronic hijacking of the RQ-170 unmanned reconnaissance aircraft, say U.S. analysts.


    Holes in the account start with the fact that it took days for the Iranians to discover the lost aircraft. In fact, intelligence officials at one point thought the Iranians might simply never stumble across the crash site because it was in such a remote and uninhabited part of northeastern Iran.


    Electronic attack of the Sentinel is “certainly possible, but there’s no indication that they even knew it had crashed in Iran for some time,” says a veteran black-projects manager.


    That scenario is validated by an aerospace industry ISR specialist, who agreed that “if they were not aware [of the Sentinel’s presence in Iran for days], then there is no reason to believe they had any semblance of control.”


    And then there are technical issues that make a hijacking, as described by the Iranians, unlikely.


    “Among the reasons to doubt the claim that GPS jamming had anything to do with the loss of the RQ-170 is a simple overlooked fact,” says a third U.S. analyst. “GPS is not the primary navigation sensor for the RQ-170 or for most other air vehicles. The vehicle gets its flight path orders from an inertial navigation system, which is essentially unjammable unless you want to monkey with the local gravitational field. The GPS updates the INS and cancels its drift. So, even a full GPS blackout would simply cause the vehicle to be a bit less accurate,” he adds.


    “If the GPS was ‘spoofed’ with a fake signal — and even JDAMs have anti-spoofing GPS receivers today, so that might be difficult — any abrupt change in the GPS reading would cause the Kalman filters in the GPS/INS to conclude that the GPS was malfunctioning and cut it out of the loop,” he says.


    The continuing discussion of why the RQ-170 went down was renewed by a Christian Science Monitor interview with Iranian military technologists who say they were able to “cut off communications links” to the Sentinel using knowledge gathered from the inspection of at least three other U.S.-operated, non-stealthy, unmanned aerial systems (UAS). The trick, they say, was to scramble the GPS coordinates that guided the aircraft to make it think it was landing at its home base in Afghanistan, and only imprecision in the altitude data caused the Sentinel to land with its wheels up.


    The report went on to quote an Iranian engineer as saying the “electronic ambush” was accomplished "by putting noise [jamming] on the communications, you force the bird into autopilot. This is where the bird loses its brain."

    Tags: ar99, RQ-170, Iran, physics

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