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Originally Posted by pdurrant
Well, Campbell gets lots and lots wrong, but the main thing for me is that he uses limitations of sea-going vessels or of aircraft for his spaceships.
The main one is his implicit assumption (eventually stated explicitly) that space ships save fuel by changing course gradually, so that their 'speed' relative to whatever situation they're in remains high. The most wasteful course, according to Campbell, is to directly reverse course.
This is sort-of true for waterships and aircraft. But not spaceships. They don't have anything for their wings or hull to press against, and so for spacecraft the most efficient was to move back the way they came (outside gravity wells) is to just flip end for end and accelerate directly in the opposite direction.
A curved course for a spacecraft is wasteful way to reverse course, as you're accelerating perpendicular to the way you want to go, twice!
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I can't remember anyone justifying this on fuel, but know that the long curve have been justified for other reasons. The two reasons I can think of are ship and engine design.
The engine design was a factor because of the difficulty of stopping and starting the engine. In that case, turning the ship to thrust in the other direction becomes an interesting manoeuvre. I know I've read a book that used this as an important point, but I can't think of what it was.
Something like the Bussard Ramjet used in Larry Niven's "Protector" has other problems. The ship was made of three separate sections connected by long cables. It's been a while since I read it, but my memory has that in normal operation, the only way to turn was using long sweeping turns. Some of this was the design of the ship, having to keep the cables taught. But, the ramjet design only works at reasonably high speeds, so other fuels or methods have to be used to get up to operating speeds.