From: mooregr@deletethisgreenms.com   
      
   "JF Mezei"  wrote in message news:ArINH.8342$ew6.7420@fx11.iad...   
   >   
   >On 2021-01-19 07:40, Jeff Findley wrote:   
   >   
   >> SpaceX made a conscious decision to avoid liquid hydrogen.  It has such   
   >> low density that it makes tanks and turbo-machinery oversized compared   
   >> to other fuels (increasing the dry mass of the stage).  It's deeply   
   >> cryogenic requiring more insulation, among other things.   
   >   
   >But does this change re-usability and require 1 moth turn around between   
   >engine firings?   
   >   
   >> I think it's fair to say that SpaceX wouldn't be interested in a LOX/LH2   
   >> engine that has to be ground started.   
   >   
   >   
   >My curiosity is more focused on what SpaceX would have done if given the   
   >SSMEs for free, if it could have easily made these engines truly   
   >re-usable and self starting.   
   >   
      
   They would have sold them for scrap.  They had no need or interest, that's   
   the entire point.   
      
   Truth is, from at least one of my sources, the SSMEss, towards the end of   
   the shuttle program were in theory good for 3 flights with very minimal   
   maintenance.   
   I suspect even that was very conservative.   
      
   Restart though was a completely different issue. And no, they probably   
   couldn't have.   
      
      
      
   >BE-E from Blue Origin is hydrogen and re-usable. So curious how much of   
   >the problems with SSMEs are NASA paperwork vs engine's specific  design   
   >vs use of hrdrogen.   
      
   A lot has to do with the specific design. Consider it partly the cost of a   
   laptop versus a similarly powered desktop, the laptop will be more expensive   
   simply because trying to fit the same performance into a smaller space is   
   costlier.   
   The SSMEs were fairly constrained by having to fit into the rear of the   
   shuttle. I suspect if the engineers had room to make things bigger, they'd   
   have been cheaper to build and easier to maintain.   
      
   --   
   Greg D. Moore                   http://greenmountainsoftware.wordpress.com/   
   CEO QuiCR: Quick, Crowdsourced Responses. http://www.quicr.net   
   IT Disaster Response -   
   https://www.amazon.com/Disaster-Response-Lessons-Learned-Field/dp/1484221834/   
      
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