From: ansible@typhoon.xnet.com   
      
   Henry Spencer  wrote:   
      
   >Some would say that the reentry problem was solved quite satisfactorily,   
   >until the aircraft nuts got their foot in the door and started insisting   
   >that spaceships had to look and act like aircraft.  The Apollo heatshield   
   >had tremendous safety margins, and a little bash from falling debris   
   >wouldn't have bothered it in the slightest (not least because the really   
   >crucial part of it wasn't exposed during launch).   
      
   Indeed.  It was buried in the middle of the spacecraft during launch and   
   in-flight.  Anything that could damage the TPS on Apollo would be doing   
   critically bad things to the rest of the spacecraft.   
      
   And even when it did take a hit, as it (probably) did with the LOX tank   
   explosion during Apollo 13, it still performed like a champ.   
      
   Design Margins.  Why is that so hard for some people to understand?   
      
   The Space Shuttle has 5 flight computers, any one of which could fly the   
   spacecraft alone.  But it only has _one_ very fragile TPS!  There were   
   people saying it was a bad design 30 years ago, and they're still not   
   being listened to.   
      
   >But ablative heatshields don't work very well if you start insisting that   
   >the vehicle has to have *wings*.  That's what killed Columbia:  the long,   
   >slow, reentry of a winged vehicle gives it a prolonged roasting rather   
   >than a quick blowtorching, requiring thermal protection that radiates heat   
   >away rather than soaking it up... and thus needs exotic high-temperature   
   >materials, which typically involve compromises in areas like physical   
   >durability.   
      
   And if the fragility of the tiles themselves weren't bad enough...   
      
   Everyone should have already read about the tremendous amount of time   
   and effort needed to maintain the Shuttle's TPS.  We're talking tens of   
   thousands of man-hours, for every flight.  I'm sorry, but that's just   
   insane.   
      
   Now compare that to the time and effort needed to attach oak blocks to   
   the bottom of a capsule.   
      
   Sure, maybe you'd need to hire Norm Abrams to work on your TPS, instead   
   of relying upon your uncle Bob who has a table saw in his garage.  But   
   we're talking several orders of magnitude easier to design and   
   impelement.   
      
   Perhaps this is slight hyperbole, but the TPS inspection could be done   
   with a hammer in 15 minutes.  Anything which falls off after being given   
   a good whack needs to be fixed.   
      
   Simple.  Robust.  Reliable.  I like it.   
      
   Sure, you can call the Chinese space program primitive.  I'd rather be   
   primitive and alive, than sophisticated and dead.   
      
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   BTW, 'reliable' isn't the same thing as 'robust'.  Lots of people forget   
   that too.   
      
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   Fuel is Cheap.  Simplicty is a Virtue.  Design Margins are Good.   
      
   How many billions have been wasted ignoring these sentiments?   
      
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   What the heck are the wings on the shuttle good for anyway?  It isn't as   
   if the SS has any kind of cross-range ability.  You can't, at the last   
   minute, abort or even pick a different runway.   
      
   James Graves   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)