And to finish things off, here’s the performance standard for GLONASS: https://glonass-iac.ru/upload/docs/stehos/stehos_en.pdf. On page 42-43 the global average positioning error is listed as 5 m horizontal and 9 m vertical. There’s also a worst site positioning error of 12 m horizontal and 25 m vertical, but I don’t think we’ll need to worry about that.
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You’ve been wonderful, I appreciate your help. I think the last thing that needs to be done is some kind of primary source that the Japanese military relies primarily on US’ GPS. Especially if it looks like their own system is instead a back-up.
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From what I found, it seems that the JSDF uses (or is planning to use) multiple navigation systems in tandem to increase robustness. For example, page 8 of Defense Programs and Budget of Japan, Overview of FY2021 Budget Request says that they are developing a common receiver for signals from Michibiki (Japanese name for QZSS), GPS, and Galileo. For a more recent primary source, page 33 of the references to the Defense of Japan 2024 white paper by the Ministry of Defense says that the Ministry of Defense and the Self-Defense Force “will
promote the use of multiple positioning signals including Quasi-Zenith Satellite System (QZSS) and commercial satellites”. In game this could mean that their GNSS bombs would use whichever system that has the highest accuracy (from the sources we’ve got so far, probably Galileo).
It appears that the JSDF might not have fully integrated QZSS into their systems yet, though perhaps they may be using it on a case by case basis, like the ship example mentioned earlier. For a source of them using GPS, page 292 of Defense of Japan 2019 says that “the MOD/SDF has mounted
GPS receiving terminals on a large number of equipment”. Similarly, page 4 of this briefing memo of the National Institute for Defense Studies from 2017 says that they had been using GPS since 1993, before which they used TRANSIT since 1986.
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Well this became quite relevant now that Gaijin decided all GNSS weapons should have an up to 10m inaccuracy.
Though it doesn’t really hurt most bombs, it hurts the GBU-39, which is a particularly small bomb, the most. I read claims of submeter accuracy, apparently because it uses differential GPS (using ground stations) to enhance accuracy. But even without those, it’s currently a bit worse.
Like stuff like these pictures (from SDB brochure) should be otherwise statistically unlikely:
In game now:
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Hmm, that definitely seems to be too inaccurate. GPS SPS should have a 1.82 m horizontal accuracy (diameter of 3.64 m). Since the Leo 2 has a width of 3.7 m and the Abrams has a width of 3.66 m, it should be able hit the tank when aiming at the centre.
At least they have a line in the code they can easily tune now to real life, but as of right now every GNSS weapon has a 10m accuracy.
This article at least says SDB uses WADGPS, which from a little bit of searching allows submeter accuracy (or even less). Makes sense, because the SDB would be incredibly ineffecive if not almost directly hitting whatever it’s targetting.
Claims JDAM has a CEP of 13m, and SDB <4m. I can tell you however that these are outdated figures (article is from 2004). JDAM has a lower CEP than that 13m figure, but the JDAM manual is very much export restricted, so can’t be used. But you can probably find it. SDB likely is submeter nowadays (with the required infrastructure available).
2015 AF magazine:
Figure matches with the JDAM manual of the same year actually. They have accepted AF magazine as valid source (secondary I guess?) in the past. 13m CEP actually is also mentioned in the manual for GPS-denied zones when using GPS guidance in anti jamming mode, maybe that is where that comes from.
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JDAM should be 1.7meter.
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It possibly can go that low, maybe they also improved it more since 2015. But quoting JDAM delivery manuals, it is a 5m CEP. Might need to check it again, but I think the only figure like 1.7m was the TLE.
I recall a primary source for the F-2’s navigation module which was just a GPS + INS one.
Might try to find it, also have some secondary sources saying the XGCS-2 uses GPS, nothing primary on that though.
I also have some document somewhere talking about combining GPS with INS for better navigational accuracy, so i dont really think they use QZSS at all.
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