[AR] Re: DARPA responsive launch challenge
- From: Henry Spencer <hspencer@xxxxxxxxxxxxx>
- To: Arocket List <arocket@xxxxxxxxxxxxx>
- Date: Mon, 23 Apr 2018 14:43:11 -0400 (EDT)
On Sun, 22 Apr 2018, Henry Vanderbilt wrote:
At least part of my point was that someone writing SF in the fifties
didn't know a fraction of what we do about what will and won't work - we
have both sixty years accumulation of practical knowledge *and* far
better access to it than a fifties SF author. Heinlein may well have
assumed it stayed stable going out the exhaust in running his numbers.
I agree in general, but I think that on this particular point, even with
the more limited knowledge of the day, there was good reason to have
doubts about that. The atomic-hydrogen torch dates back to the 1920s, for
example.
(Hey, at least he ran some numbers - more than most did, and it showed
in a lot of those books.)
Indeed so, but sometimes he didn't realize he should run numbers on some
issue, or he did it but got things wrong.
(Uwe just mentioned "Blowups Happen". Most people who've read that story,
have read only the revised version rather than the original -- he did some
touchup work on it for postwar book publication. The "Expanded Universe"
collection has the original, along with a comment by Heinlein saying that
in hindsight, he preferred that one. The most interesting difference is
that the original says how big the world-wrecking worst-case explosion
would be: 100 million tons of conventional explosive. He presumably
calculated that from the published information on fission. It's roughly a
factor of 2 too high for his mass of U-235 -- he may have confused total
energy release with energy per fission fragment, or worked from a source
which did -- but that aside, it's about right. But the idea that a 100MT
explosion would wreck the world is, of course, just hopelessly wrong --
maybe he didn't know how explosion effects scale, maybe he messed up a
decimal point when calculating, maybe he didn't calculate and made the
beginner's error of just vaguely assuming it would be linear so a hundred
million is a Really Scary Number. Big boom, yes, and not something you
want to be anywhere near, but aside from fallout, the ranges of the
adverse effects would be measured in tens of kilometers, not thousands.)
Henry
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