XPost: sci.astro, sci.physics, sci.space.policy   
   From: fjmccall@gmail.com   
      
   willner@cfa.harvard.edu (Steve Willner) wrote on Fri, 15 Jun 2018   
   18:59:07 -0000 (UTC):   
      
   >> >The [JWST] telescope is folded, not only the solar arrays.   
   >   
   >In particular the 6.5-m primary mirror is folded as well as many   
   >other pieces.  It's frightening to watch the deployment videos.   
   >   
   >In article ,   
   > Fred J. McCall  writes:   
   >> And THAT is because you cannot make a single mirror that large to   
   >> adequate precision,   
   >   
   >At least three observatories with seven telescopes in active use will   
   >be surprised to learn that.  Not to mention additional ones planned.   
   >   
      
   You can do things with earthbound scopes that you cannot do with   
   something you're going to shoot into space.   
      
   >   
   >Every JWST presentation I've seen that mentioned the subject said   
   >that using a deployable (folding) mirror is because the Ariane 5   
   >shroud is too small to fit a 6.5-m mirror.  I wouldn't be surprised   
   >if there are "black" programs with the same difficulty.   
   >   
      
   Nope.  They use a mirror roughly the size of Hubble's.  Remember,   
   they're looking at something relatively close as such things go.   
      
   >   
   >That said, this particular use case doesn't necessarily justify a   
   >rockoon approach, which will be difficult at best for large boosters.   
   >   
      
   Yes.  The point is that a balloon does NOT replace a 'first stage'.   
      
      
   --   
   "The reasonable man adapts himself to the world; the unreasonable   
    man persists in trying to adapt the world to himself. Therefore,   
    all progress depends on the unreasonable man."   
                                         --George Bernard Shaw   
      
   --- SoupGate-Win32 v1.05   
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