If North Korea launches an ICBM or multiple ICBMs towards America, could the US military disrupt targeting by shutting down the GPS for a period of time ?
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GPS has never been the only game in town. The Russian GLOSNOSS system and the Chinese BeiDou could also be used.
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Most ICBM’s don’t use GPS; they use inertial navigation. The North Koreans will probably have surveyed launch sites in advance, so its not like GPS will be of much use.
I have no idea how the guidance systems on North Korean missiles work (most militaries don’t tend to publish that kind of information), but I seriously doubt that they use GPS. Typically, a guided missile like that uses some sort of navigational computer that includes some sort of inertial measurement unit so that the missile can sense its exact movements.
And it’s not like they’re all that dependent on guidance, anyway. Almost does count in nuclear war, and North Korea’s likely targets are all pretty close, too.
True, with the yield from a nuke it’s not exactly required to be pin point. Plus, factor in a surface or aerial blast then you can be off probably by several miles?
I’ve read stuff but don’t know how viable, that they used camera based guidance that locked on to star positions to calibrate and recalculate the trajectory?
I’d think that any type of inertial or GPS based system could be spoofed in some way.
Can’t think of a way to spoof inertial guidance, since such a system doesn’t rely on any information/signals from outside the vehicle itself.
Called a star tracker. Anything that flies in space that cares about its attitude has one - so pretty much anything that flies in space. I don’t know that an ICBM these days needs one (and the technology is subject to ITAR export restrictions) if ground based. A long time ago I worked a bit on the Trident program - submarine launched missiles absolutely do need them because of the uncertainty of the missile position at launch. A ground based missile should know its position pretty accurately, so it depends on how accurate the intertial navigation is.
Although nuclear weapons are quite devastating compared to even the most powerful conventional ordnance, being “close enough” only applies to soft targets such as cities and urban manufacturing facilities attacked with weapons in the multi-hundred kiloton to megaton range. When it comes to hardened strategic targets such as underground silos, command facilities, or communication hubs, or mobile targets for tactical strikes, accuracy is important, hence the efforts put into inertial guidance systems of the LGM-30 F/G ‘Minuteman II/III’, LGM-118A ‘Peacekeeper’, and UGM-133A ‘Trident II D-5’ systems, as well as precise location or point of origin, which required developing geodetic systems with highly precise local mass concentrations which are well beyond the need of any other space application.
The Trident system does use astro-inertial naviagation, using its “Star-Sighting” system (basically an advanced star tracker, if by advanced you mean compared to the technology circa 1985). This corrects for errors in launch position and any accumulated errors during flight before release of the Mk. 4 and Mk. 5 reentry vehicles (containing the W-76 and W-88 weapons respectively) to their multiple independent targets. No ICBM used the Global Positioning System for navigations specifically because of the potential vulnerability, but GPS is used for Tomahawk and the now-retired Gryphon GLCM cruise missiles but only as an enhancement to TERCOM and inertial navigation. (Test flights of ICBM and SLBM systems due have GPS receivers but only for range tracking so that if the inertial navigation system fails and themissile flies off-course it can be quickly detected and destructed.)
Inertial guidance cannot be spoofed by any means short of producing a new gravity gradient, and if you can move million ton masses about at will or have a Lunar-mass black hole at your disposal you probably have the upper hand in any strategic conflict regardless.
Stranger
Well, not quite everything: There are other ways to get attitude information. Some small satellites, for instance, have a powerful magnet on board to line them up with Earth’s magnetic field, and you can also get some information just from the relative power generation of various solar panels (though I suppose that, technically, that’s a form of star tracking, too).
And precision might be needed for hardened targets, but I can’t imagine North Korea trying for one of those anyway. Going after silos or the like only makes sense if you have enough warheads to take out all of them, plus some plan for bombers and subs.
The newest long range Russian ballistic missiles like the ICBM-ranged SLBM ‘Layner’ (R-29RMU2) and projected ICBM RS28 do use GLONASS as part of their guidance, per public sources. The shorter ranged Iskander is said to use either GPS (perhaps in export versions) or GLONASS. The experimental conventional version of the US SLBM Trident, which never entered service as far as is known publicly, used GPS to reduce CEP to what would work with a non-explosive warhead. That’s besides use of GPS for range tracking and other missile test (targets for Ballistic Missile Defense) purposes in US BM’s as mentioned.
But for the North Koreans I think the question sort of answers itself. If the weapon is being developed as a major strategic effort to threaten/deter the US, then it wouldn’t seem wise to rely on a system the US could, at least in theory (lots of practical problems to overcome), selectively shut down and the US might eventually find out the NK system did rely on GPS. The US itself doesn’t rely on GPS for its operational nuclear BM’s, and in the Russian BM systems using satellite systems it’s an add on: the missiles presumably still basically work if GLONASS/GPS is shut down and there are presumably measures built in to resist spoofing, ie prevent the sat nav input from taking the missile far from where the (astro-) inertial system would tell it to go.
Measures of the Earth’s magnetic field might provide basic orientation of the craft but wouldn’t be precise enough to get a good estimate of orbital elements and speed due to variability and uncertainty in the geomagnetic field. Measuring solar incidence on solar panels, on the other hand, can give some pretty precise estimates provided you have a reasonable initial estimate of the ephemeris, especially if you have panels deployed on opposite sides of the spacecraft, allowing you to get precise measurements of Earth’s umbra.
The weapons so far demonstrated by North Korea are barely more powerful than tactical weapons, and while 20 to 30 kT TNT equivalent yield is large by conventional standards, the direct effects of the thermal pulse wouldn’t even consume even the entire city center of Seoul or Inchon; if the weapon were detonated 5kft the center of Yongsan-Gu, the primary thermal and blast effects would barely extend into the neighboring districts, and the extimated initial casualties would be less than 200k people. There would be other radiation and secondary firestorm hazards. Realistically, I suspect it would be problematic for North Korea to deploy a reliable nuclear weapon by ballistic missile, period, but they’re clearly not at the point of developing high yield pure or boosted fission weapons, much less megaton-grade thermonuclear fusion city busters.
Stranger
For GPS/GLONASS guidance to work requires two things (1) Receiving the signal and updating the inertial guidance solution (2) A maneuvering RV or bus to import those small delta V changes during the mid-course phase.
Early first generation ICBMs like Atlas did not have an RV or bus to impart those fine-tuned trajectory changes, hence RV accuracy was dependent on precise booster performance. Just after the boost phase the velocity could be tweaked by small vernier engines but they would cut off then most of the trip had no further adjustments. So the question is do less-sophisticated ICBMs today even have RVs capable of mid-course corrections? Both that plus GPS guidance updates would be needed.
Even with perfect mid-course guidance and trajectory correction, unpredictable atmospheric anomalies may contribute about 200 feet targeting error during reentry. Reducing this would require something totally different – precision guidance and steering during atmospheric reentry. Those are called MAneuvering Reentry Vehicles (MARVs). The conventional Trident would have modified an existing RV to be maneuverable, plus GPS terminal guidance. Due to reentry blackout the guidance data might have been downlinked from a satellite above. The difficulty of modifying the existing Trident RV supposedly prevented further development and testing.
However a few experimental U.S. MARVs were tested from 1979-1981. This article has a photograph of a MARV reentry trajectory, which shows a sharp turn. The literature has discussed MARV maneuvering ability of 100 g or more, which is consistent with the photograph: Maneuverable reentry vehicle - Wikipedia
Well… it does seem that a combination of GPS/inertial guidance system is highly resilient to anything aside from an EMP or something at that level. Maybe fly another ICBm with a nose mounted CIWS.
Do you have a source for the last sentence? My understanding is that Congressional reluctance to fund ‘CTM’ (Conventional Trident Modification), for potentially valid arms control reasons, is what killed it before it progressed to being able to overcome technical issues or not.
Not necessarily directly relevant to the DPRK right now, though perhaps partly relevant, there’s a disturbing tendency sometimes in US defense discussion IME to view technical challenges the US hasn’t been able to or more often hasn’t bothered to put full effort into getting past (CMT, AFAIK) as not feasible. It comes up in a lot of amateur discussion about how Chinese long range antiship BM’s which ‘couldn’t’ work because of the blackout during re-entry…unless they’ve solved or gotten around that issue. Oxygen torpedoes weren’t viewed as feasible enough to pursue by the USN pre WWII.
As to the Russian systems, Iskander is a far below ICBM range so the warhead is moving a lot slower and much less of a technical issue for GLONASS/GPS to provide guidance all the way down. I haven’t seen it discussed in open source exactly how the newer generation big Russian BM’s use GLONASS as part of their guidance, but it’s widely reported they do. Separately there’s a lot of reported activity by the Russians in MARV’s, but not clear how the two things fit together, to my knowledge.
That is true but by some accounts the technical problems were possibly not solvable. This is because they were trying to modify existing RVs with aero surfaces and GPS hardware that worked during reentry (apparently for both conventional and guidance-improved nuclear versions). Obviously you can develop a brand new RV design which does that but funding constraints evidently precluded that:
Are earth’s mass concentrations large enough to have a meaningful effect on the trajectory of an ICBM?
Another thing to consider is that I really doubt the DPRK has concerns in regards to accuracy within the hundreds of feet. Their primary objective is to have a nuclear ICBM that can get to an “enemy” and if they a within 50 miles of the target they’ll be ecstatic.