SpaceX-owned satellite system Starlink has proved crucial for communication within the Ukrainian military. Russia has clearly recognised its utility, too: Ukraine’s adversary has managed to procure terminals illegally, and in recent weeks, Starlink has started to crack down on that use, initially imposing a speed limit of 75km/h over Ukraine to limit use of the system in Russian drones, and in the last day reportedly cutting off access to those Russian troops altogether.
But Starlink’s owner is not the only one who seems to be able to control its satellites. As protesters in Iran – facing an internet shutdown – turned to Starlink to communicate with the outside world, the Iranian government succeeded in disabling it for periods in parts of Iran. How?
Strictly speaking, the Iranian government did not jam Starlink’s signal.
The system “is an absolute nightmare to jam,” said Dr Thomas Withington, a RUSI Associate Fellow and expert on electronic warfare. It is a comparatively strong signal which operates at a high radio frequency, giving a “needle-sharp beam” picked up by small antennae.
“The beam is so fine and the antennae are so small that if you’re going to jam it, you have to be around 20 meters away to have any hope of getting your beam onto that antenna,” he said.
In November, Chinese researchers simulated how to disable Starlink over an area the size of Taiwan for twelve hours. While they concluded it was theoretically possible, the paper also laid bare the scale of the challenge. Jamming Starlink over a country of this size would be a “Herculean task,” said Withington.
Rather than jamming Starlink’s signal, the Iranian government seems to have instead done the much easier task of jamming GPS – a service that Starlink terminals need in order to work properly.
Starlink needs GPS for two functions. Firstly, the terminal on the ground needs to know its location to know which satellite to connect to at a certain moment. A Starlink terminal uses phased array antennas, which contains over a thousand components adjusted by software. The system needs to acquire a GPS signal to adjust to face the nearest satellite.
Secondly, the system needs a precise time signal to synchronize the terminal with the satellites, which is provided by GPS. The satellite and terminal “need to both agree what the time is, so that they can then send information to and from each other,” said Withington.
“If you start to jam that GPS signal, any Starlink terminal within range will really struggle to connect with the satellite, and it has a great deal of difficulty being used for communications,” Withington said.
The Iranian government seems to have jammed GPS signals in areas it believed were Starlink terminals. There may be technical workarounds using an external time source or by patching in a timing signal from a terminal in an area not being jammed. But these would be complicated.
“It becomes quite a cumbersome exercise – Starlink terminals were never really designed to be used like that,” said Withington. “It’s a civilian system, not a military-grade one. It was never really designed to be used in an electromagnetically-contested environment.”
Military-grade systems would be designed to be resilient in such environments, and have access to alternative PNT signals which are much harder to jam.
Russia has used GPS interference against Starlink in Ukraine before, but it has limitations. The first is that Russia’s own Starlink terminals nearby would be affected.
But even a regime not using Starlink itself would be significantly impacted by GPS interference. The Iranian security services themselves likely need GPS or some other GNSS. “When you jam, you’re invariably going to risk jamming yourself. So you also restrict your ability to respond to those protests, to coordinate your own security forces,” said Withington.
What’s new about the Iran case is the tactic employed, he added: using electronic warfare against civilian protesters.
“We tend to think about EW being used on the battlefield. It’s a military tool by and large. This possibly is a portent of what may happen in the future. Other regimes will be taking note.”
There is a more general question here about the resilience of LEO satellites. Proliferated into hundreds or thousands of satellites broadcasting at a high frequency that is difficult to jam, LEO satcom constellations are not without vulnerabilities.
LEO constellation OneWeb is one of the two backup systems Taiwan has in case of severe damage to its undersea cables.
Analysts say that it would be possible for China to disrupt OneWeb around Taiwan using large-scale GPS jamming. They disagree on the strategic assessment: whether China would try to jam GPS across Taiwan or use a more precise, targeted approach focused on jamming known single points of failure in key infrastructure like the power grid.
The former could be done from ships initially, but to sustain the energy needed for prolonged jamming would likely require a permanent ground jamming station, as Russia has in at least two locations around the Baltic. There seems to be no concrete proof of one in Fujian province, but it would be difficult for analysts to identify until it was actually used. What we do know is that China has experimented with GPS interference: there are recorded instances of GPS anomalies in the East China Sea and demonstrated uses of jamming for counterdrone purposes.
GPS reliance is not the only vulnerability of LEO satcom systems.
For these kinds of high-frequency radio systems, it is generally possible to detect the location of a terminal while it is transmitting.
Withington said that, because of the challenge of jamming LEO systems, militaries may conclude that the simplest response is just to target the terminals. “It may just be that if you see a Starlink terminal on the battlefield, ultimately, the easiest thing is just to get a drone to drop a grenade on it,” said Withington.
Because their location can be detected, training is critical too: users need to be disciplined and careful about how they use such systems.
Taiwan’s second satellite communication backup system is SES, which analysts say is not reliant on GPS. However, it has its own vulnerabilities.
“A single service is never a resilient option: satellites have vulnerabilities, and cables [do too],” said Dr Crystal Tu, an Assistant Research Fellow at Taiwan’s INDSR. “There’s no single resilient service, there’s only a resilient communication plan.”
