Except: The balloon doesn’t have a huge infrared signature. No big ass turbine engine with a 1300º hot section like your usual targets
and its a multi-celled fabric sheathe
and it’s going so slow it’s almost standing still (a problem they had in vietnam going against prop fighters w/ jets. you don’t have a lot of wiggle room)
So you can try to…..approach from the sunward side and hope that the surface is warm enough for your IR to make it out against the -40º temps and howling winds that surround it (which, BTW, your missile is likely at the very edge of its envelope too, meant to be used in air 3x more dense for its promised performance)