GPS Anti-Jamming

We’ve discussed the vulnerability of US military platforms and weapons to GPS denial (see, "GPS Jamming").  Now, here’s the flip side of the discussion – the GPS anti-jamming capability which may enable GPS signal utilization even in the face of GPS jamming.

Here’s an interesting summary of the GPS problem.

“On Earth, the GPS satellite signal is received about 30 decibels below the background noise level. This translates to a signal strength of about 1,000 times weaker than that of thermal noise normally inherent in electronic equipment. Conventional GPS digital signal processing allows receivers to pluck these signals out of the background noise. When interference raises the level of background noise, however, a receiver may be unable to track the GPS signal.

This problem is especially acute with low-end receivers using omnidirectional antennas. These antennas lack the ability to provide directional discrimination away from sources of interference and toward satellites. Interference sources can be narrowband—affecting only a small part of the overall GPS frequency spectrum—or they can be broadband, affecting the full GPS spectrum. The civilian GPS arena is particularly susceptible to narrowband interference, as it occupies only 2 megahertz of spectrum. Military GPS is spread across 20 megahertz.” (1)

Thus, the fairly concentrated and very low signal power of GPS allows for easy, low power jamming.  So much for the problem.

One solution to defeating GPS jamming is to enhance the receivers signal processing, allowing it to directionally align with GPS satellites and to process the signal to enhance it.  An example of this approach is Lockheed Martin’s GPS spatial temporal anti-jam receiver (G-STAR).

“G-STAR currently is effective against a wide range of GPS jamming environments. Its software-driven nature also permits easier upgrades as new threats emerge. The version that is equipping JASSM consumes only 52 watts of power. It weighs 25 pounds and measures 10 inches by 15 inches by 2 inches.” (1)

“G-STAR also will incorporate the so-called selective availability and anti spoofing module (SAASM), which the Defense Department has made mandatory-beginning in October 2002-for all military GPS receivers that receive the encrypted precision satellite signal.

The SAASM module is a microelectronic device with a large number of digital components that allows an authorized user to receive the precision encrypted GPS signal.” (2)

Here’s a little more detail on GPS anti-jamming for those of you who are interested in a slightly deeper dive.

“Most anti-jam devices currently in use are either "nulling" or "beamforming systems," explained Kelly [James J. Kelly, director of advanced engineering at Telephonics Command Systems]. These two technologies refer to exploit techniques that can be used to counter jamming signals. Some GPS receivers have an antenna array, with up to seven receiving elements arrayed in a geometric pattern. Upon detection of jamming interference, part of the antenna pattern can be turned down, so the noise from that particular direction does not interfere with the rest of the system. That is called nulling the signal.

"A null means that I will not look in the direction in space that the jammer is coming from," Kelly said. The electronics protect the receiver by eliminating the interference signal. One problem with this nulling technique, however, is that "as you eliminate jammers, you eliminate your ability to receive signals from the GPS satellites," he said. "You could have a nulling system that kills off the jammers, but you no longer have enough satellites available for you to navigate."

The beamformer, meanwhile, "doesn't care where the jammers are." The beamformer selects and receives signals from at least four satellites and provides four anti-jam solutions. "The beamformer algorithm is more aggressive and you get a better result," Kelly said. Recent simulations conducted by Telephonics, he said, showed that beamformers performed better than nullers.

But these systems cannot be used with older GPS receivers. Because a beamformer produces four outputs directed at four selected satellites, it cannot interface with a standard GPS receiver that only has one input. "You need a receiver that is customized to accommodate the beamformer interface," said Kelly.

New missiles typically feature a tight package composed of an anti-jam device, antenna and GPS receiver. This makes them more adaptable for beamforming anti-jammers, Kelly asserted.” (2)

That the military is working on GPS anti-jamming is good news.  It offers the possibility that we may be able to continue to use GPS even in the face of electronic countermeasures.  Of course, we also have to recognize that the entire GPS satellite system is vulnerable.  Russia and China both claim to have anti-satellite weapons and China has pretty well demonstrated their capability.  If an enemy can destroy our satellites then having an anti-jamming capability won’t mean anything.

It’s also not enough to simply develop an anti-jamming device that can theoretically work.  We need to subject whatever is developed to rigorous testing – far more rigorous than the testing we’ve subjected our other weapon systems to.  We need to throw the best jamming capability we possess against it and see if it actually works in a combat environment.  Ideally, we would clandestinely test it in the real world in places like Ukraine, against actual Russian ECM.

Finally, we can’t simply develop a device, congratulate ourselves, and think that our navigation is secure.  Our enemies are continually working to develop new methods of GPS denial and we may find out the hard way that our anti-jamming isn’t as effective as we thought.  This means that we have to keep working on alternate navigation methods.  Every ship, plane, and missile should have multiple navigation systems so that if one is denied we have an alternate available.  In other words, we have to plan for failure – something we have not done in recent decades.

Inexplicably, not everyone is searching for GPS alternative capabilities.  Notably, the Air Force has limited interest.  Terry Little, Air Force program manager for JASSM, has this to say,

“In the JASSM program, we are not interested in an alternative guidance technology to GPS.” (2)

Well, that’s about as plain a statement as you could want.  Hopefully, that philosophy is not indicative of the military as a whole.

I’m encouraged that the military is recognizing the vulnerability of GPS and is working to protect the capability.  Given the ease of jamming and the physical vulnerability of the GPS satellite system to anti-satellite destruction, we need to continue working on alternate guidance systems. 

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(1)Signal AFCEA website, “Jam-Proof Signals To Guide Navigation”, Robert Ackerman, November 2001,

http://www.afcea.org/content/?q=jam-proof-signals-guide-navigation

(2)National Defense website, “Threat to Satellite Signals Fuels Demand for Anti-Jam Products”, Sandra I. Erwin, June 2000,

http://www.nationaldefensemagazine.org/archive/2000/June/Pages/Threat4358.aspx

Russian GPS Jammer

We’ve talked a great deal about the US military’s blind obsession with electronics and networks and their susceptibility to disruption.  Despite this, the US continues to increase their dependence on electronics.  We’ve noted, in passing, the Russian’s heavy use of electronic warfare in Ukraine although details are sparse.  The US Army is certainly worried and is frantically initiating multiple electronic warfare measures and training – a belated good, for them.  Now, we see this article from a Russian website about deployment of a GPS jamming device called POLE-21.

“An integrated jamming system to screen strategic facilities from cruise missiles, smart bombs and drones using GPS, …” (1)

Any Russian pronouncement has to be taken with extreme caution but this development seems both plausible and inevitable.

The issue is not the absolute accuracy of the report but rather the fact that this is one more warning to the US military to begin weaning themselves off their electronic and GPS dependence.  Nearly every ranged weapon in the US inventory uses GPS.  An enemy who can effectively neutralize GPS signals either through jamming, disruption, false signal injection, or satellite destruction will have neutralized a huge portion of our weapon inventory.  Some of our weapons, especially the newer ones, can also utilize inertial navigation, terrain mapping, and other forms of guidance, however, the accuracy falls off significantly.

We need to begin developing other forms of guidance while simultaneously hardening the guidance systems we have.  The world is preparing for high end war and we’re preparing to fight idiots in the back of pickup trucks.  We need to wake up.

Related note:  Birds can navigate thousands of miles during migrations and wind up in the exact same spot year after year.  Salmon return to the exact spot they were born to spawn.  Nature abounds with examples of precision navigation that rival our best electronics.  There are other possible methods of guidance.  We would do well to investigate them!

 

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(1)Sputnik website, “Silent Protector: Russia Develops Hi-Tech Jammer to Block Enemy Electronics”, 25-Aug-2016,
http://sputniknews.com/russia/20160825/1044633778/russia-jammer-electronics.html

Stealth for Dummies

Continuing the highly acclaimed (according to ComNavOps' brother-in-law) “Dummies” series, we turn our attention to stealth in warship design.  Just as there was (there isn’t now since they’ve all read the Armor for Dummies post and have been educated !) a group of people who, misguidedly, believed that armor was pointless because it couldn’t totally stop every weapon in existence, so too, there is a group of people (probably the same group) who believes that stealth is pointless since it can’t make a warship completely invisible.  Such a belief could not be more wrong and we’ll now see why.

Most people believe that the purpose of stealth is to conceal the location of a ship – if you can’t find it you can’t attack it.  That’s great except that the naysayers will point out, correctly, that it’s not possible to completely hide a ship with stealth measures.  You can reduce the radar (or visible, or infrared, or electromagnetic) signature to some degree but any ship can be detected.  Let’s face it, we can’t completely mask aircraft and ships are many times larger.  Further, some aspects of ship design just don’t lend themselves to enhanced stealth.  The hull just plain has to be a big vertical chunk of metal.  We can slope the sides somewhat but the hull is still a big radar return.  The same goes for the superstructure.  The various sensors and weapons offer large radar returns and their signatures can’t really be reduced all that much without adversely impacting their function.  Ships need cranes, boats, and deck gear all of which increases the ship’s signature.  So, there’s no getting around the fact that a ship can’t be made invisible.

So, why do we even bother with stealth?  Well, we can reduce the ship’s signature and every bit of reduction makes the ship just that much harder to find.  For a ship attempting to penetrate an enemy A2/AD zone, every hour it can avoid detection is an hour less time the enemy has to attack it or reposition assets to deal with it.  Every hour undetected is an hour of safety making it more likely that the ship will be able to carry out its mission. 

Further, in order to overcome stealth, the enemy will be forced to employ more subs, patrol boats, AEW, and search assets in attempt to increase the density of their search coverage.  This soaks up assets that might otherwise be employed offensively.  So, stealth requires the enemy to assume a larger, more defensive posture than they would prefer.



Enough of a Good Thing or Too Much?



Sooner or later, though, the ship will be found.  What then?  Well, this is where stealth serves its second purpose - a purpose most people overlook.  When a ship is found, what is required to attack it?  The location is, by definition, now known but modern weapons require more than that.  They require a target lock for terminal guidance of the weapon.  That lock may take the form of radar returns, infrared, or whatever.  If the weapon can’t achieve a lock, it won’t strike its target.  It’s that simple.  We could park a ship ten miles off an enemy’s coast, broadcast its location, and, if the stealth measures were good enough, the ship would be invulnerable because the enemy weapons couldn’t lock on.

Is warship stealth that good?  Not hardly! 

So, again, what’s the point of stealth if we can’t totally prevent target lock?  Consider a group of missiles launched towards our ship whose location is reasonably accurately known.  The missiles will be spread out and some will approach the ship on the fringe of the missile’s detection radius.  Stealth reduces that detection radius so that some of the missiles that might otherwise have locked on will miss, never having seen a target.  Of course, some of the missiles will approach dead on and will achieve target lock.  Bad day to be on our ship, huh?  Not necessarily.  Even those missiles that achieve a target lock will have the strength of that lock reduced due to the ship’s stealth.  That allows the ship’s passive defenses such as chaff, flares, and ECM to be more effective.  In other words, a missile with a weak lock is more susceptible to being decoyed than one with a strong lock.  Of course, some missiles will still maintain a sufficient lock for a terminal attack and that’s why ships carry point defense weapons.  Nothing, including stealth, is perfect!

We see, then, that stealth serves not one, but two purposes:  making detection more difficult and degrading weapon locks.  It’s the second purpose, degrading weapon locks, that strikes me as the more important.  In combat, ships will be found.  It’s what happens after that that really matters.  Will the ship survive the inevitable combat to carry out its mission and, hopefully, return home?  Stealth increases the chances of survival.  The notion that stealth must completely hide a ship in order to be worthwhile is just as silly as the idea that armor must completely stop all weapons. 

Like armor, which carries a weight penalty, stealth carries a cost penalty.  Stealth designs are more complex, a bit harder to build, require some additional equipment, and, most significantly, reduce available deck space (look at any stealth warship and compare it to a WWII conventional ship and you’ll see what I mean – the LCS is an extreme example of a stealthy ship that has very little horizontal deck space for mounting weapons, sensors, and gear).  Still, the penalties are well worth it and can be compensated for.  Of course, there’s a balance point in the stealth cost-benefit relationship.  Where that point is, I don’t know.  Has the Zumwalt gone too far?  Only time will tell.

Clearly, stealth enhances the survivability of warships and does so at relatively little cost.  Hey, throw in some armor and you’re on your way to a good ship design!

GPS - The Navy's Addiction



GPS - Achilles' Heel?



One of the simultaneous strengths and weaknesses of modern missiles, UAVs, and weapon systems and platforms in general is the use of GPS (Global Positioning System).  The common GPS that is part of our cell phones and automobile navigation systems among other commercial devices is also at the heart of the targeting systems of military weapons.  GPS, both commercial and military, is provided by satellite systems.  Unfortunately, those satellites are vulnerable to destruction and jamming.  For example, it is generally assumed that GPS satellites will be taken out early in a war with China.  If that were to happen, it would render the Navy’s missiles useless or, at least, severely degraded with only Inertial Navigation Systems (INS), which are far less accurate, to fall back on.



On a related note, the Navy now relies so heavily on GPS for ship movement and location that most ships would be lost without it.  In fact, the USS Port Royal grounding was due, in part, to loss of GPS and the resulting lack of awareness of their location.

Here’s a portion of a recent article from Katie Drummond that highlights the issue. (1)

“In an effort to stave off the looming threat of GPS attacks, the Pentagon's asking for ideas to replace the system ... or at least give it some slicker, more reliable back-up.

The navigational system used by the military for just about everything from guiding drones to dropping bombs is increasingly under threat of attack. Now, the Pentagon’s desperate to replace it. Or, at least, reinforce it enough to stave off a looming storm of strikes.

That’s the thrust of a new venture from Darpa, the military’s premier research arm and the brains behind GPS’ initial development in the 1950s. On Tuesday, the agency announced the second phase of their program, “All Source Positioning and Navigation (ASPN),” that’s trying to “enable low-cost, robust and seamless navigation solutions … with or without GPS.”

The program, which Darpa quietly kicked off last year with two awards for theoretical research, is one part of a larger military effort that’s trying to steer the Pentagon away from its GPS dependency.

Why? First off, there’s the growing risk of GPS signals being jammed by adversarial forces. Enemies on the ground can also “spoof” a GPS system — essentially tricking it into showing an incorrect location. And these are far from hypothetical risks: Mere weeks ago, a fatal drone crash in South Korea was attributed to GPS signal jamming from north of the border. Last year, Iranians (perhaps dubiously) claimed they jammed the GPS signals navigating an American spy drone, then spoofed the system to land in Iran’s clutches.

And those GPS-thwarting capabilities continue to grow — at a pace that’s exceeded the military’s ability to keep pace — largely because of a booming commercial market for GPS-jamming technology. Such electronic warfare “was once the province of a few peer-adversaries,” Darpa deputy director Ken Gabriel told the House Armed Services Committee’s panel on emerging threats earlier this year. “It is now possible to purchase commercial off-the-shelf components for more than 90 percent of the electronics needed in an [electronic warfare] system.”

The risks now inherent in GPS are well-known, but it doesn’t look like Darpa’s ready to give up on the system altogether. Instead, they’re after a navigational system that can swiftly move between different combos of devices, using a “plug-and-play” approach. Right now, the agency notes, the military’s navigation systems primarily rely on a pairing of two devices: GPS, which uses satellite data, and what’s known as an Inertial Navigation System (INS), which relies on “dead reckoning” (using estimates of speed and direction, without external references) to provide locational intel.

It’s a tactic that’s accompanied by several problems. For one, INS — because it uses internal, ongoing estimates — is notoriously error-prone without a GPS system to back it up, so it can’t be relied upon exclusively. And INS systems often obtain their starting position and velocity from a GPS device. Which means if the GPS is under attack, the INS risks leading military personnel (or the drone or weapon they’re navigating) astray.

These navigational systems are also extremely inflexible. Typically, Darpa notes, they’re programmed to accommodate, maybe, one additional sensor (say, a magnetometer) and unable to plug into any others. As a result, personnel can’t respond to “new threats or mission challenges” in real time. Not to mention that, even as consumer navigation tech becomes more sophisticated (Apple Maps, anyone?) the military can’t take advantage of the most cutting-edge products.

Of course, there are already plenty of GPS alternatives available. Radio beacons, which transmit signals from static locations to receiving devices, allow the calculation of location based on proximity to various beacons. Ground feature navigation extracts the positions of tracked objects and then uses them as points of reference to gauge a vessel’s locale. And stellar navigation systems use the coordinates of celestial bodies to assist in a vehicle’s navigation.

Darpa’s dream navigational system would go beyond those kinds of discreet systems — by incorporating pretty much all of them. The ASPN system, according to Darpa’s announcement, should be able to accomodate any available sensor, and be versatile enough to incorporate new sensors “as they become available in the marketplace.” The key benefit to such adaptability would be the mitigation of GPS-dependency. Personnel would instead have myriad sensors at their disposal, and be able to toggle between them as necessary. In other words, a suite of backup tools to work, in conjunction, as a safety net in case of GPS failure. Among the ton of gadgets that Darpa wants the system to utilize: 3-D imagers, LiDAR, temperature sensors … and good old compasses.”



The Wave of the Future?



As an example of the military’s recognition of the inherent weakness in depending on GPS, DARPA awarded a contract to Lockheed Martin to develop a next generation anti-ship missile, the Long Range Anti-Ship Missile (LRASM) which will be able to target without using GPS.



The Navy needs to wean itself off its dependence on GPS or risk finding itself with lost ships and non-functional weapons at the start of the next war.  Anyone got a sextant?

(1) “When GPS Goes Down, Pentagon Still Wants a Way to Fight”, Katie Drummond, June 13, 2012