If GPS is gone then yes, wwe'd have to rely on internal INS. Since they'd be updated before flight, I have difficulty believing today's ring laser gyros (or whatever they use now, if the RLG has been replaced) will drift 30m during a flight of an hour or three or even twelve. But I don't know and maybe you have some knowledge in that area (in which case you have more than I). If that's true, then yes the JDAMs using INS only will be off their aimpoints a significant amount by today's standards, and many targets would need multiple bombs or need to be restruck after the first. In that situation I think we would return to using LGBs for many of the targets that require pin-point accuracy. If GPS is only being denied near the target area (due to jamming somehow), then the aircraft will have been updating in flight, and so even though the bombs might not be able to use GPS accuracy would still only degrade somewhat. I believe they would remain sufficiently accurate to handle most targets with a single bomb. Displacedjim

Thanks for the response. I picked the 10m, 30m numbers out of the air assumming the aircraft flew for several hours and manuvered violently (-5g,+2g) before release of the weapon. I seem to remember that RLG accuracy is measured in angle per unit time (drift rate). i.e (a random example) 1 mil per hour[1] for tactical aircraft[2]. (drift rate) * (number of hours) * (distance of flight) = error (1/6400)*5hrs*3000nm=2.3nm The exact figure for each device I think varies with g load (perhaps even rate of change of g load?). I guess the aircraft INS which this discussion would move onto would be 100x better than the tactical aircraft RLG I give above. 2.4nm in meters is 4.5km [3], a system one hundred times better than those considered marketable in ther early 1980's would have a error of 45m in this example. Specifics are not available for operatational systems so I guess this won't go any further. [1]"Fibre Optic Rotation Sensors and related technologies", Ezekeil (MIT) & Arditty (Thompson-CSF), P432, Fig 2, Springer-Verlag 1982 [2]http://www.answers.com/topic/angular-mil [3]http://en.wikipedia.org/wiki/Nautical_mile

All I gotta say about GPS jamming can be summed up in three words. Home On Jam :)

hybrid, home on this; http://lumen.georgetown.edu/projects/postertool/index.cfm?fuseaction=poster.display&posterID=873 Now think if the US will really vaporize people on a suspicion/best guess of who ordered the bang(s). More importantly does MAD deter anybody who doesn't value their own life - or their compatriots! Methinks we got our HAND's full in a few short years!

It doesn't matter how much Aircraft's INS crawls during flight if the target is aquired by aircraft's sensors and JDAM flies INS-only. JDAM wil get the same coordrantes the plane is using and because it's all about relative poisitions the coordinates could differ miles from real ones, but the JDAM could still miss only some 10-30m. I know one modern RLG INS assembly, made in the US and used in US fighters, costs nearly $500k apiece. It will drift a couple dozen meters per flight hour if not updated from other source (like GPS or by pilot flying over known landmark). The whole JDAM-guidance kit costs some $20k so I would guess that the RLG assembly inside JDAM has a bit lower accuracy. (But ofcourse it is designed to keep its position only a minute or so)