The edge of space

[wolram]

http://www.sciencedaily.com/releases/2009/04/090409142301.htm

Where does space begin? Scientists at the University of Calgary have created a new instrument that is able to track the transition between the relatively gentle winds of Earth's atmosphere and the more violent flows of charged particles in space – flows that can reach speeds well over 1000 km/hr. And they have accomplished this in unprecedented detail.

 

[Xnn]

With that data, U of C scientists confirmed that space begins 118 km above Earth and the results were published this week in the Journal of Geophysical Research.

So, the X-15 never really make it to outer space.