[Goose]

I think I read somewhere that they found they could not program the Mig 29 hardware to use our JDAMS and came up with the work around. I also had the impression that the weapon could be reprogrammed from a laptop in the cockpit, I have no idea if that is correct.  Here is another link.  I apologize if it is the identical info: https://armyrecognition.com/focus-analys...rsk-bridge

It isn't identical. It has some different information. I also believe you are correct that there is an article out there that shows a tablet PC and a handheld GPS (strapped to a canopy support strut) that can be used with JDAMS. If memory servers it was not on a MIG-29 but rather an SU-27. https://www.forbes.com/sites/davidaxe/20...ide-bombs/. The article states that the JDAM has to know its location and speed when it is dropped. To do that, the article discusses the Mil-std 1760 C interface. The following link is a very good one. Those interested in how all this works should definitely read it. https://en.wikipedia.org/wiki/MIL-STD-1760.

It is NOT TRUE that the JDAM needs to know its altitude and speed (in 3d vector space) when dropped. It will perform better if it does. If it doesn't get the initial data it will use GPS to derive an approximation to initialize the INS. The INS can derive roll, pitch and yaw all by itself if necessary, but will do  better if it has initial values. If GPS is available all the way to the target, the INS initialization error won't matter much. The CEP will not be as good as it might have been, but it will still be "very close" to spec. If the GPS is not available sometime after launch, the initial INS bias error will matter to some degree.

The GPS on a NATO aircraft is much better than the GPS in your cell phone or the one in the JDAM itself. So is the INS of the NATO aircraft. The aircraft GPS can wok in the presence of jamming that will disable the JDAM GPS. The NATO launch platform can give an initial setting for the JDAM from its GPS if it is working. If GPS isn't working, the NATO aircraft can transfer its INS position, which is probably "pretty good". A Soviet era aircraft has none of these things and has no 1553 bus. It is possible Ukraine fished the wiring for a 1553 bus out to the hardpoints where the JDAMs live. The GPS hanging above the tablet PC isn't in the same league as say an F-16 GPS. It doesn't supply the code offsets and the 1 Pulse Per Second (1 PPS) signal needed to synchronize the code offsets with the GPS in the JDAM. It may supply the satellite numbers it is using. While Ukraine can do lots of things, the limitations of the underlying platform are real. IMO it is unlikely the tablet PC can provide a "quality" JDAM INS and GPS initialization. I suspect it is up to the JDAM to find the target. A bridge is big enough target that accumulated INS error and initial values bias won't matter much. The fact Ukraine can launch the JDAM at all is a major accomplishment.

[Goose]

I think I read somewhere that they found they could not program the Mig 29 hardware to use our JDAMS and came up with the work around. I also had the impression that the weapon could be reprogrammed from a laptop in the cockpit, I have no idea if that is correct.  Here is another link.  I apologize if it is the identical info: https://armyrecognition.com/focus-analys...rsk-bridge

It isn't identical. It has some different information. I also believe you are correct that there is an article out there that shows a tablet PC and a handheld GPS (strapped to a canopy support strut) that can be used with JDAMS. If memory servers it was not on a MIG-29 but rather an SU-27. https://www.forbes.com/sites/davidaxe/20...ide-bombs/. The article states that the JDAM has to know its location and speed when it is dropped. To do that, the article discusses the Mil-std 1760 C interface. The following link is a very good one. Those interested in how all this works should definitely read it. https://en.wikipedia.org/wiki/MIL-STD-1760.

It is NOT TRUE that the JDAM needs to know its altitude and speed (in 3d vector space) when dropped. It will perform better if it does. If it doesn't get the initial data it will use GPS to derive an approximation to initialize the INS. The INS can derive roll, pitch and yaw all by itself if necessary, but will do  better if it has initial values. If GPS is available all the way to the target, the INS initialization error won't matter much. The CEP will not be as good as it might have been, but it will still be "very close" to spec. If the GPS is not available sometime after launch, the initial INS bias error will matter to some degree.

The GPS on a NATO aircraft is much better than the GPS in your cell phone or the one in the JDAM itself. So is the INS of the NATO aircraft. The aircraft GPS can wok in the presence of jamming that will disable the JDAM GPS. The NATO launch platform can give an initial setting for the JDAM from its GPS if it is working. If GPS isn't working, the NATO aircraft can transfer its INS position, which is probably "pretty good". A Soviet era aircraft has none of these things and has no 1553 bus. It is possible Ukraine fished the wiring for a 1553 bus out to the hardpoints where the JDAMs live. The GPS hanging above the tablet PC isn't in the same league as say an F-16 GPS. It doesn't supply the code offsets and the 1 Pulse Per Second (1 PPS) signal needed to synchronize the code offsets with the GPS in the JDAM. It may supply the satellite numbers it is using. While Ukraine can do lots of things, the limitations of the underlying platform are real. IMO it is unlikely the tablet PC can provide a "quality" JDAM INS and GPS initialization. I suspect it is up to the JDAM to find the target. A bridge is big enough target that accumulated INS error and initial values bias won't matter much. The fact Ukraine can launch the JDAM at all is a major accomplishment.