"but can it stay airborne for 20 or more hours, like the P-3?"
First from several years ago read my original blog entry, that P-3 Orion naval patrol plane of venerable but very accomplished war plane.
Described as a "patrol" plane but also having an impressive offensive capability as well. During that era of the Cold War the P-3 even able to deliver nuclear munitions [depth charges].
That P-3 Orion as stated and for some time at the end of expected life expectancy, now being slowly but surely taken out of service.
Secondly read this very recent StrategyPage web site article, that P-3 acknowledged as a real winner of some repute.
And of course a replacement for the Orion now in the works, the prototypes now operational [?] and flying, that replacement also based on a venerable and somewhat dated but nonetheless WINNING AIRFRAME.
"Older But Safer"
"August 11, 2013: Recently a U.S. Navy maritime patrol squadron (VP-45) achieved a rare feat, 44 years of flying without a mishap (an accident that costs more than $2 million to repair). That’s over 265,000 flight hours without loss. The squadron has long had a reputation for being fanatic about maintenance and quality control. Despite the advancing age of its P-3 aircraft, that sort of effort paid off."
As has been previously noted, the P-3 based in large measure on the original design of the Electra commercial turbo-prop aircraft. Electra not such a world-beater with a lot of mishaps, that NOT being the case however with the P-3.
The P-3 having been repeatedly refurbished, rebuilt, and modified, often at a cost of $10 million per aircraft!
P-3 now being phased out of service, that replacement as designated the P-8, a jet aircraft based on the civilian Boeing 737 design.
That 737 commercial version first having flown in 1965. The basic concept and design at least fifty years old, but a proven and worthy airplane!
"The P-8A is based on the widely used Boeing 737 airliner. Although the Boeing 737 based P-8A is a two engine jet, compared to the four engine turboprop P-3, it is a more capable plane."
Presumably these brand-new P-8 will indeed be BRAND NEW! Having just come off the assembly line? One would like to think so.
"The 737 has, like the P-3, been equipped with hard points on the wings for torpedoes or missiles. The B-737 is a more modern design and has been used successfully since the 1960s by commercial aviation. Navy aviators are confident that it will be as reliable as the P-3. The Boeing 737 first flew in 1965, and over 5,000 have been built. The P-8A will be the first 737 designed with a bomb bay and four wing racks for weapons. The P-8 costs about $275 million each."
Poseidon [P-8] again as with the P-3 having an offensive capability but not anymore nuclear I would think! Undoubtedly too there will be an export market for this warplane!
That cost of a brand-new P-8 NOT CHEAP! Anything but that. Will not I would think not to be acquired in staggering numbers. The P-8 too that cost mostly from the electronic suites what they are called. Electronic devices and apparatus, entire systems that bulk of the cost for ONE PLANE!
Good luck P-8!