Originally Posted by
tartare
As the author speculates, I suspect this jet is testing technologies to be used in environments where positioning, navigation and timing are completely denied.
Probably B-21 related.
Quite possible. The very first 757 (NA001) was retained by Boeing - back during the F-22 development it sprouted some strange looking wing like extensions and other appendages near the nose. Supposedly it was being used to flight test and develop some F-22 software.
Some details here:
https://theaviationist.com/2017/05/3...alth-aircraft/