XPost: sci.space.shuttle   
   From: henry@spsystems.net   
      
   In article <1111465715.822367.58070@g14g2000cwa.googlegroups.com>,   
     wrote:   
   >A titanium structure would weigh less...   
      
   No, substantially more -- NASA estimated an extra 2t -- although that   
   would be more than made up by lighter thermal protection.   
      
   >NASA did study this option.  Why did they pick aluminum?  Was it just   
   >the cost of titanium fabrication.   
      
   They balanced the extra costs of working with titanium against lighter and   
   lower-maintenance thermal protection, and decided that there was very   
   little overall difference.  The decisive factor, in the end, was that the   
   USAF was worried about the limits of US titanium production and processing   
   facilities, especially with production starting on the F-15 (which used a   
   fair amount of it), and didn't want to see NASA using titanium in   
   quantity.   
      
   >...It would also seem to me that the reduction in weight would be   
   >nice, and help with either added payload, higher orbits, larger return   
   >payload, and safer aborts.   
      
   At the point when this decision was being made, orbiter size was still   
   vague, so it wouldn't have made a difference in payload -- aluminum just   
   required a slightly larger orbiter.   
      
   >Anyone know .. is it some exotic alloy of aluminum, or just standard   
   >aircraft grade aluminum?   
      
   Pretty standard alloys -- mostly 2024, if I recall correctly.  There's   
   some titanium, in particular in the engine thrust structure, and some   
   composites, notably the cargo-bay doors.   
   --   
   "Think outside the box -- the box isn't our friend."    |   Henry Spencer   
                                   -- George Herbert       | henry@spsystems.net   
      
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