Every 4,700 flight-hours, U-2 spy planes need maintenance. And to do that, technicians have to disassemble the entire plane, piece by piece, and inspect a huge number of components.Forty-thousand rivets and 1,800 revised parts later, the plane's repainted, reassembled, and ready for duty.The U-2 was invented over 60 years ago, but its security and capacity keeps it from being phased out. Last year, the US Air Force was weighing alternatives. Should it keep the U-2 or use Global Hawk recon drones instead? Though drones do cost less money to operate ($8,000 less per flight hour compared to the U-2), the best course of action isn't clear—U-2s can carry bigger payloads, and aren't susceptible to cyberattacks like drones can be.Watching this, it's hard to see how a physical hacker could get through such a complex plane.