'Largest aircraft in the world' seen over US. What is it doing?

Pathfinder 1 looks like a blimp, but much bigger. It's part of a wave of interest in "lighter-than-air" or LTA aircraft.
Autocar on MSN

Top 10: Largest Fighter aircraft of the Second World War

The Junkers Ju 88 is so versatile that it seems contractually obligated to appear in every "Top 10 Second World War Aircraft" ...