In article ,
Pat Flannery wrote:
Just done in a small fraction of the cost of the X15 and able
to carry more people.

...but it exists for the sake of ego as much as anything else; let's see
it try to go Mach 6 in the atmosphere sometime....

But why would you want to do that?

Note that even the X-15 ended up struggling to answer that question, after
the steady climb of combat aircraft up the Mach-number scale stopped.
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |