I can't find that tag MISR either. Military Intelligence Special Reconaissance?
It's an E-8C Joint STARS.
"The Northrop Grumman E-8 Joint Surveillance Target Attack Radar System is a United States Air Force Airborne ground surveillance, battle management and command and control aircraft. It tracks ground vehicles and some aircraft, collects imagery, and relays tactical pictures to ground and air theater commanders."
I would guess it's some kind of reconaissance mission or possibly training. You could post in Planefagging101 and maybe someone who knows will chime in.
Sorry I don't have a firm answer for you.