“Interesting that the SDB seems more jam resistant when air launched”
Fighter Pilot previously expressed his credible theory about that, but it went over my head at th time.
I believe it was something like the plane can give the bomb an accurate start point, from which it can calculate its whole flight, but the ground launched pops up and looks for GPS to get its bearings.
Aircraft position data is transferred to the SDB via the 1553 databus architecture.
My guess is that HIMARs launchers are not 1553 compliant.
The "designers" of the GLSDB decided that the GLSDB could achieve a GPS lock on after launch, like the Excalibur.
In a GPS jammed environment, this does not work.
I believe there is a "simple" solution whereby a 1553 compliant computer would pass position data to the GLSDB just prior to launch.