Buckeye's mission, which as a drone it has no choice but to accept, is to test out aeroservoelastic technology, which is how the plane's controls adapt to structures bending and wobbling during flight. It's a complex problem that NASA's been trying to tackle for years--the agency hopes to develop new kinds of lightweight, flexible aircraft, but that flexibility can come with the tradeoff of having less control over moving parts. A big flying wing gives them a great testbed for learning how to balance flexibility and control.