XPost: sci.military.moderated   
   From: jdnicoll@panix.com   
      
   In article ,   
   John Schilling  wrote:   
   >   
   >The book many people here are referring to and nobody is actually   
   >naming because everybody assumes everybody else knows what it is,   
   >is Robert A. Heinlein's "The Moon is a Harsh Mistress", published   
   >in 1966.   
   >   
   	snip   
      
   >The general plot is that, in 2076-as-forecast-from-1966, the denizens   
   >of a Lunar penal colony decide they've had enough of taking orders   
   >from Earth and organize a revolution.  The particular bit that is   
   >relevant here is their choice of weaponry - they can make small arms   
   >locally, but their way of bringing the war to Earth is to use an   
   >electromagnetic catapult that used to launch hundred-ton cargo barges   
   >on an Earthward trajectory, to launch hundred-ton rocks instead.   
   >   
   >A hundred tons of rock free-falling from the Moon to the Earth will   
   >arrive with, and liberate on impact, kinetic energy comparable to   
   >the Hiroshima Slum Clearance Event.  So it makes for a nice show of   
   >force.   
   >   
   >Unfortunately, this is one of those parts that's a bit dated.  In   
   >1966, it was a reasonably well thought extrapolation, but in the   
   >years since people who can afford to put more time into doing the   
   >math than can even a diligent SF writer have found the relevant   
   >scaling laws: electromagnetic catapults get a *lot* more expensive   
   >as you make the payload bigger, and only a little more expensive   
   >as you make the repetition rate higher.   
      
   	There's also a serious problem that RAH overestimated some   
   of the physical effects of high velocity impactors. One example would   
   be a strike near the UK which is supposed to cause problems up the   
   Thames. Unfortunately, if you run the numbers, the ripple that hits   
   London is a couple of inches high, maybe.   
      
   	RAH could have BOTECed this from Glasstone's _The Effects of   
   Nuclear Weapons_ but I don't of any evidence he owned a copy.   
      
      
   >So anything built for mercantile rather than military purposes, as   
   >was the original lunar catapult in tMiaHM, will be designed to launch   
   >hundred-pound buckets every second rather than hundred-ton barges every   
   >hour.  And a hundred-pound projectile will shed almost all of its energy   
   >harmlessly in the upper atmosphere.   
   >   
   	There's also the question of why exactly someone would design a   
   grain barge of any size to be able to reach the ground at Mach 25. What   
   possible good could come of this?   
      
      
   >Still a good story, you just have to remember that much of the technical   
   >extrapolation is obsolete.   
      
   	IMO, the last good novel RAH wrote, ignoring the squicky bits.   
      
   --   
   "The keywords for tonight are Caution and Flammability."   
   							JFK, _Bubba Ho Tep_   
      
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