[noiseman]

I think these researchers may just be “inventing” a technology that’s already operational in the black projects world. Remember the unexplained sonic booms over California a number of years ago, and the sightings of “donuts on a rope” contrails that accompanied them? The best guess of most knowledgeable observers was that these were flights of a hypersonic aircraft using a pulse detonation wave engine.

[MHGinTN]

I witnessed a string of ‘puffs’ at high altitude several years ago when on night sky watch. I think the aircraft was called Aurora.