Stuff That Never Made It - but why?

[McColm]

So,
If the tunnel/bridge ideas failed the former President Ronald Reagan announced in 1986 in his State of the Union message calling for development of "...a new Orient Express that could, by the end of the next decade, take off from Dulles Airport and accelerate up to twenty-five times the speed of sound, attaining low earth orbit or flying to Tokyo within two hours..."

This idea wasn't new a similar project had been cancelled in the 60s due to cost and technical difficulties.

Aerospatiale and Dassault were major contractors for Heremes but this was cancelled in 1993. It was designed to be launched into low earth orbit by an Ariane 5 booster and intended to support the European elements of the International Space Station.

The Germans have come up with the Sanger involving an unmanned/manned turbo-ramjet-powered first stage mothership that would carry the second stage reusable manned vehicle or disposable cargo carrier to a height of 98,000ft/3,000m at a speed of mach 6. the second stage would use its rocket in order to reach orbit.

The X-30 National Aerospace Plane (NASP) was the public follow-on to the classified Defense Advanced Research Projects Agency (DARPA) Copper Canyon program of 1982-1985. The program was to develop an single-stage-to-orbit, horizontal takeoff/horizontal landing, air-breathing scramjet manned vehicle. Flight testing was due to begin in 1990.
Engineers believed that the speed of mach 25 wasn't achievable and that a  limited top speed of mach 17 could be maintained. Estimates of the cost for the project are between $10 to $20 billion.
The development work carried out has led to the scramjet in the disguise of the so called Aurora.

[kitnut617]

I think a bigger problem would be plate tectonics, as the continents drift apart they would stretch the tunnel.

I was thinking that myself Dave, only just recently I was reading about this, in the Atlantic they're drifting apart at an average speed of your fingernail's growth and in a good year your hair growth (or is that the other way around ? ).  IIRC that's about 12 to 25mm a year, just think where we stand on the earth today, a million years ago we would have been 12-25 kilometers away.

http://www.geography-site.co.uk/pages/physical/earth/images/plates.gif