Hi all,
(this discussion is getting rather circular)

Recently, Don French posted:
(largely snipped)

[...] In a vacuum, the thrust required to accelerate from
Mach 0.5 to 1.0 is exactly the same force required to accelerate from
Mach 9.5 to Mach 10.0.

The problem, of course, is that scramjets don't operate in a vacuum.

For what it is worth, there isn't a lot of air at 100,000 feet.

Then, what, exactly is the scramjet "breathing", and what, exactly, is
heating the leading edges of the surfaces to 2600°? Seems to be quite a
lot of air to me.

I really don't understand why aviators would rather diminish the
accomplishment than come to an understanding of it.

Neil