"Len" wrote in message

Rumor has it that the Aurora aircraft makes a contrail like that.
Supposedly it is powered by a pulse jet engine or some sort of external
combustion powerplant.

That was the rumor. If not Aurora, some other project out there. There
were a few projects like Pumpkinseed and other test beds where, for example
the fuel was ignited on the external, trailing surface of the aircraft but
the "donut" contrail does suggest a pulse jet.

An acquaintance of mine who would know told me at Edwards that one of the
Aurora birds, (if not THE bird) crashed and the program was eventually
cancelled. That doesn't mean that another similar project might not be
underway presently.

Aurora has been discussed on occasion in Aviation Leak and Spy Technology.
No tinfoil hat required; the US government still tests aerospace technology.

-c