they say it doesn't exist but thats BS, we've all seen that long vapor trail that planes leave in the sky, but there is another trail that is left from scram jet technology, if you see a vapor trail then a clear spot then vapor trail in a long stretch that would be from scram jet technology or *cough* cough* the Aurora project, but rumor is that the aurora project is its supose to fly in lower outer space so it can shoot down satilites, and enemy aircraft from way above without detection, but who knows, just remember the F-117 was designed in the late 60's early 70's and first flew in 1977 and the F-22 first flew in the late 80's early 90's so the projects now are probably badass