I saw this on CNN today.

For months, US intelligence and military personnel in Iraq have been raising alarms about the risk to American forces from these newer, more sophisticated Iranian-made drones. Rather than being guided by a pilot from a remote location, some of these small, fixed-wing drones use GPS navigation, making them far less visible to US surveillance systems and impervious to jamming.

I understand how an independent guidance system is probably jam-proof, but how does using GPS make the drones less visible? Don't all military drones rely on GPS?

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    $\begingroup$ Assuming that CNN knows what they're talking about with regard to aviation and military matters is, increasingly, a hit-or-miss proposition. Many of their "journalists" report on things without even considering the (considerable) depths of their own ignorance. $\endgroup$
    – Ralph J
    Jun 28 '21 at 19:30
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    $\begingroup$ Assuming that anything said on CNN, or any TV news outlet, is even vaguely coherent is a mistake ! $\endgroup$
    – Fattie
    Jun 29 '21 at 12:44
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    $\begingroup$ The key bit is: "far less visible to US surveillance systems" - those systems 'look' for Infra-Red and Radio signals, rather than just what the human eye can see. $\endgroup$ Jun 29 '21 at 13:51
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    $\begingroup$ "impervious to jamming" Even for CNN that's some pretty incorrect information. $\endgroup$
    – user
    Jun 29 '21 at 15:33
  • $\begingroup$ It’s a rare news article that gets anything right about aviation. $\endgroup$
    – MD88Fan
    Jul 1 '21 at 16:58

For being remotely controlled, drones need to emit and receive a radio signal. If the outgoing signal contains a video feed, it will be high bandwidth and be like a beacon announcing the location of the drone. By pre-programming the flight path and using GPS location fixes, the drone will be passive and not emit radio signals.

Before GPS, high precision navigation needed an active radar system which would scan the surrounding terrain and compare the results with an onboard map. Such navigation systems were used by cruise missiles but, by relying on an actively emitted signal, would announce their presence to suitably tuned receivers.

While it is true that such a passive drone cannot be jammed, it is still possible to spoof the GPS signal or to jam the GPS signal itself, leaving the drone navigation system only with dead reckoning in the vicinity of its target. Also, when no communication with the drone is possible, it will only follow a pre-programmed pattern and not be able to respond intelligently to a changed situation. Such spoofing has been demonstrated by the Iranians in 2011 when they diverted a US drone officially flying over Afghanistan and when misleading tankers in the strait of Hormuz recently.

Not all drones rely on GPS since there are alternatives (GLONASS, BeiDou or NavIC), apart from active systems like Terrain Contour Matching (TERCOM).

  • $\begingroup$ Inertial navigation is probably also a good alternative (especially when worried about interference), but I'm not sure if that is actually used in drones. $\endgroup$
    – Bianfable
    Jun 28 '21 at 18:03
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    $\begingroup$ @Bianfable Inertial navigation is the basis of dead reckoning but becomes progressively unreliable with time due to drift. It needs a GPS fix now and then to eliminate drift. $\endgroup$ Jun 28 '21 at 18:12
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    $\begingroup$ @Bianfable I would think that yes, because the 1 Hz refresh rate of GPS with random jitter around current position is insufficient for the flight control system so it needs the gyroscopes and accelerometers anyway, but the accuracy won't be good enough for the final targeting. $\endgroup$
    – Jan Hudec
    Jun 28 '21 at 18:13
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    $\begingroup$ @JanHudec there's nothing inherently 1Hz about GPS or any GNSS system, and many receivers offer between 5 and 20 updates per second. $\endgroup$
    – hobbs
    Jun 29 '21 at 4:40
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    $\begingroup$ @MSalters For detecting spoofing, your software must anticipate it. The RQ-170 back in 2011 did certainly not. Next, once spoofing is detected, who do you trust? Your INS will still drift and make the navigation unreliable. Once the spoofed signal drones out the real one, you have no GNSS signal you can trust. $\endgroup$ Jun 29 '21 at 10:25

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