Thanks for the links. Shame that Nick Cook raises the "doughnuts on a rope" contrail. I've got my *own* photos of one of those. After taking the photos I checked on flightradar24 and found that the contrail corresponded *precisely* with the flightpath of a 747 that had just gone over. Another couple of minutes prodding the web produced this:
At which point I was done with *that*.
Regarding the weather satellite photo (which doesn't actually explain how they calculated the speed) an aircraft travelling at those speeds would also have to be up at about 200,000 feet or something, unless built of unobtainium. But contrails form between 25K and 40K (source: Wikipedia). Seems unlikely (but not impossible) that they would form at 200K.
The thing that really stands out about that "contrail" is that it is absolutely straight (bearing in mind curvature of earth - but it mirrors the state boundaries that are based on latitudes). In other words, a ballistic trajectory. So a meteor would seem a more plausible explanation. Would an aircraft - even unmanned - travel for *thousands* of miles without a course correction?
The other stuff is essentially speculative. It would be extraordinary for this aircraft to be in operation for three *decades* without any concrete evidence coming to light. It would take hundreds, nay thousands of personnel to build and operate it. Yet nobody credible has come forward.
Having said that, I had an airline pilot describe seeing a weird triangular aircraft to me. As he said, he was used to looking up at aircraft and identifying them. I can't ask him about it any more as he "shuffled off" about five years ago.
And then there's the compelling argument that the US military wouldn't have given up the SR-71 unless they had a replacement.