U2 vs Global Hawk. U2 is winning the funding

The U2 recon manned recon aircraft has been flying for a long time.  It became famous in the the 1950's when Francis Gary Powers was shot down over Sverdlovsk, Russia, flying a secret photo recon mission, violating Russian airspace big time.  U2 is still flying.  It's main claim to fame is fantastic altitude capability, 70,000 feet or better.  Few fighters can reach that high.
   A new fangled competitor is a drone, Northrup Grumman's Global Hawk, a big drone with a bulbous nose.  For a while the high tech drone looked to replace the vintage U2 for photo recon.  But this fiscal year the Pentagon changed it's mind, it wants to dump Global Hawk and keep flying the U2.
   One argument is Global Hawk now has a lower cost per flying hour. Used to be, both U2 and Global Hawk cost about $33,000 per hour to fly.  Last year, Global Hawk claimed to have reduced its cost per flyng hour to $25,000.  This is attributed to an INCREASE in Global Hawk flying hours.
   This makes me think the computation of cost per flying hour is too crude to be much use.  It doesn't get cheaper when you fly more.  What's gotta be happening is they divided FIXED costs by flying hours.  In this case, yeah cost per flying hour goes down.  They largest fixed cost is the money spent to buy the drone in the first place.  They probably  just assume a 20 year service life, and tack on a fixed cost per year of 5% of the acquisition cost (depreciation) .  That's crude.
   The drones have a fatigue life, the number of flying hours before stress and vibration cause dangerous cracking of the structure.  The proper  depreciation should be the acquisition cost pro rated by the percent of airframe hours used up.  Fly more and your depreciation goes up.   
   One thing about Global Hawk, it ain't all that reliable.  Last year 55% of Global Hawk missions were canceled.  Whereas only 4% of U2 missions were scrubbed.