They issued such commands in advance of the Taepodong (Unha 2) launch and other provocations in the last year and a year or two ago (the “shoot down authorization”). They are just excelerating their announcement of it, and their preparations, it seems, and taking no chances. It is extremely academic if they can hit one, but they very well may be able to get a modified scud or Nodong on Musudan and bring it down either over the Sea between DPRK and Korea, or somewhere over Japanese land, hopefully not near a populated area. To do so I would say they would be very lucky. However, perhaps the threat alone and the issuing of it tonight on national TV if anything ups the ante and is good, I would like to see the Fat One think twice about aiming it at Japan with the prospect it could end up as good scrap metal in mid air. But it would take some mighty savvy shooting by the Japanese (or has been pointed out, US could get from an AEGIS ship perhaps and then give Japan the credit), or nobody would talk about it and of course DPRK’s telemetry would tell them our side got one of theirs in mid air and they will from now on be challenged and not allowed to send these over Japanese territory like they have done one 2 occasions now with inpunity.
I wish Japan were allowed to man up and build up their defense and a Nuclear arsenal, that should put the scare into North Korea, China, and Russia... a strong Japan.
They're only going to shoot down a missile launch if it fails (particularly true of the PAC-3s). The current Aegis BMD missile has very limited capability against the Musudan going to it's full estimated range, so the Norks could lob one OVER Japan with very little chance of it being intercepted.