I too have watched a shuttle launch, STS-101 Atlantis. As a flight goes down-range they look like they are traveling slow but you know they hauling butt.
I can see the Vandenbereg launches from my living room and while I didn’t witness this incident it sure looks like a launch to me.
Also, the UFO doesn't seem to be traveling very far before the upper level winds distort the contrail a lot. It looks to me like it's traveling at subsonic speeds. An ICBM would be into multiple mach speeds at that altitude.
I still think it was an aircraft.
I was talking about the initial ascent of the Shuttle viewed from five miles away.
Obviously the further away one is the slower everything appears; which is why the comment that some mistook it for a missile because of their viewing angle is so absurd.
ML/NJ