XPost: sci.space.policy   
   From: g_d_pusch_remove_underscores@xnet.com   
      
   alexterrell@yahoo.com (Alex Terrell) writes:   
      
   > raf@tiki-lounge.com (Ross A. Finlayson) wrote in message news:   
   3c6b9c1e.0401280532.705845fd@posting.google.com>...   
   >> alexterrell@yahoo.com (Alex Terrell) wrote in message   
   >> news:...   
   [...]   
   >>   
   >> I research the mass driver a little.   
   >>   
   >> Three trillion and twenty years is ridiculous, except maybe for the   
   >> people mover.   
   >   
   > I've always considered an Earth launch mass driver as impractical,   
   > due to atmospheric heating.   
      
   Launching from the ground is not _completely_ beyond the realm   
   of technical possibility. For example, according to one estimate,   
   if you used a mass-driver to lob a telephone-pole size rod of   
   ordinary solid steel at about Mach 28--30 and could somehow keep it   
   from tumbling, it would only lose about a meter or so of its length   
   while punching out of the atmosphere. If it were protected with 10--20 cm   
   of sacrificial carbon-carbon heat shield, similar to the one used to   
   protect the Galileo atmospheric entry probe, one could get the whole thing   
   into orbit essentially intact.   
      
   The _real_ problems with attempting surface mass-driver launches are:   
      
   1.)  The ridiculous accelerations involved, which would severely limit   
      what sorts of cargoes could be launched, and   
      
   2.)  The atmospheric shock waves it would produce, which would cause   
      complaints and lawsuits from many hundreds of kilometers around the   
      mass-driver site.   
      
      
   > I suppose you could have a mass driver booster, which launched payloads   
   > at 2km/s, whereupon a rocket takes over.   
      
   Doesn't ameliorate the shock-wave problem, unless you use something like   
   Keith Loftsrom's "Launch loop" to get it above the bulk of the atmosphere,   
   of have unreasonably strong but light materials such as diamondoid so that   
   you can implement something like J. Storrs Hall's concept of a mass-driver   
   perched on the tops of unreasonably tall towers.   
      
      
   > But as many have pointed out, the key to space colonisation is to make   
   > the maximum use of resources that are (energetically) close to space,   
   > which, in the short term means high Earth orbit. The nearest objects   
   > are NEO/NEAs (Near Earth Objects/Asteroids) followed by the moon.   
      
   Agreed.   
      
      
   -- Gordon D. Pusch   
      
   perl -e '$_ = "gdpusch\@NO.xnet.SPAM.com\n"; s/NO\.//; s/SPAM\.//; print;'   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)