It's very easy to dramatically underestimate the amount of fuel needed for an effective suborbital trajectory. If you want to travel half-way round the world, then delta-V wise, you're not very far off actually getting into orbit.
That article quotes 7km/s for a 10,000km trip, compared to about 8km/s for LEO.
The X-15 (and SpaceshipOne, for that matter) was never trying to actually go anywhere; it just hopped out of the atmosphere and come down again very close to where it took off, with a delta-V of about 1.5km/s.
It's worth getting a copy of KSP and actually trying this. It's eye-opening.
http://www.thespacereview.com/article/1118/1
That article quotes 7km/s for a 10,000km trip, compared to about 8km/s for LEO.
The X-15 (and SpaceshipOne, for that matter) was never trying to actually go anywhere; it just hopped out of the atmosphere and come down again very close to where it took off, with a delta-V of about 1.5km/s.
It's worth getting a copy of KSP and actually trying this. It's eye-opening.