US: LM Skunk Works & Unknown UAV

 Located near USAF Plant 42, MSI on 04 December 2011 show a very interesting imagery signature at Lockheed Martin's Advanced Development Program Facility (aka Skunk Works). Although the signature above does not conform to any known UAV, it's possible this could be anything from a mock-up to a failed design. (However, if it were a mock-up, why would LM feel the need to cover it?)

Measurements taken from imagery suggests the craft is roughly the same size as the RQ-170 at 4.8 meters while the wingspan is considerably larger--when compared to open source estimates--at 16.60 meters. 

Any and all comments are welcome.