Launching Ramp

> The column of water , if falling from 1000 feet in a 12 foot diameter
pipe,
> can accelerate air in a 2 foot diameter pipe to Mach 1.

Most impressive! 300 meters (~1000 feet) is a trivial altitude, and in many
places you can find much higher mountains stepping down to near-sea-level.
So you can pipe a high lake/water course to your tube (which would have the
lower end at sea level and the upper end at 300 m) and, after launch, just
flush out the water into the sea.

I know at least one place in my country with those characteristics, the
coastline where the Brazilian Highlands (see
http://www.peakware.com/encyclopedia/ranges/brazil.htm) "fall" steeply into
the Atlantic. Plenty of rainfall at the top, with abundance of water
courses. I guess that there is some place like that in the US - along the
Rockies?

Lucio Coelho