Jim Kingdon wrote:

Now, I don't happen to know just where the X-1 and X-15 score on
those metrics. Just to pick one I could quickly find: 199
missions over 10 years (
http://www.hq.nasa.gov/office/pao/Hi...15/chrono.html )
isn't much by aircraft standards, but it is still more than just
about any launcher (with the possible exception of a few Russian
models).

No, sorry. Various Atlas models flew 342 times during the same period
that the X-15 was flying. Various Thor/Delta models flew 318 times.

Jim Davis