David Thompson
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December 17, 2007



Twas once a British idea: http://en.wikipedia.org/wiki/HOTOL



Thanks for that. I still have a soft spot for the SR-71, which is, I think, one of the most handsome and impressive aircraft to be built.


I used to work with a chap who previously work for British Aerospace on various projects including Hotol. He was a mine of information on any space age technology. For example after I watched some TV documentary on small detonation nuclear propulsion, he gave me enough information to know he was already an expert.


He was a big advocate of Space elevators. In theory you would moor an asteroid in space tethered to the earth by a long (and very strong cable). An elevator would climb the cable to space. There were several hurdles to cross, the least of is the raising (or more likely lowering) of the cable to earth. No material strong enough exists. The asteroid would have to be in geostationary orbit to avoid falling to earth, which means a cable of about 22,000 miles length (according to http://en.wikipedia.org/wiki/Geostationary). Another problem is that such a long cable would cause devastation should it snap and fall. Therefore the cable should be tethered in a region of the Earth where the damage would be acceptable, say near Birmingham.



Tethering asteroids seems an awful lot of trouble to go to. I mean just to destroy Birmingham.

The nuclear propulsion entry is interesting, though. I notice Ted Taylor gets a mention. He worked on the early atmospheric tests in Nevada and famously used a parabolic mirror to focus the glare of a 14 kiloton explosion and light his cigarette. Which, I guess, makes him a real hombre and the coolest guy on Earth.


Flying at Mach 15, you could get from London to Chicago in 24 minutes. The question is, would you arrive relaxed and refreshed, or looking like Don Knotts?


To quote a pundit of some years ago, Scramjets have, like nuclear fusion, been 10 years from service "and always will be". The problem has always been how to test them - you need a wind tunnel capable of creating a sustained Mach 5 flow, and that is a very tall order. Any air-breathing propulsion engine is ultimately limited by temperature. A ramjet slows the air to subsonic speeds, and burns fuel in the flow. At about Mach 5, the air is heated up by the compression to temperatures limited by the materials the engine is made from, so you cannot add any energy by burning fuel without destroying the engine.

A scramjet is ultimately limited by the time the fuel takes to burn, which determines the length of the combustion chamber. There are also increasing difficulties with flow stability as speed increases. The whole bottom of the aircraft is engine, with the forebody compressing the flow and the afterbody expanding it. But the killer is what happens if the engine coughs or flames out at speed. This can induce a high pitching moment that could throw the aircraft into violent uncontrolled motion and probably destruction.

The X-29 was to have been scramjet powered all the way to orbit (Mach 25), but that was an absurd enterprise, probably conducted to conceal a black programme.

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