Very, very cool.

I wish I was alive & among those aeronautical engineers back then. I knew of the X-15 program already, but didn't know of the anniversary. Always a great story.

This is half way to the orbit of the space shuttle, and it was only 20 years after breaking the sound barrier! It would have been sure in another 20 years we'd have commercial flights to space stations. I would not have predicted an information revolution.

All kinds of fascinating things like this back in the 60s.

What became the SR-71 Blackbird is a case in point. They even mentioned it in the X-15 article linked here. Looks like nothing else in the air.

Thanks for posting this straightline.

Made so many models of these types of things back then :)

Excellent! I've known about this as a kid, having read about it in the Guiness world records book.

What they don't tell you in that book are the shocking details:
Mach 5.5: Even at high altitude the air molecules can’t get out of the way fast enough to dissipate heat. So chunks of Knight’s X-15 begin to burn and fall off. Big chunks.
Mach 6.6: A big part of the X-15A-2’s ventral fin ignites and burns completely through. It flies off the aircraft, tracing a bright, burning arc to the desert floor.

There's no doubt in my mind why nobody's tried to better this record!