From: jfindley@cinci.nospam.rr.com   
      
   In article , snidely.too@gmail.com   
   says...   
   >   
   > After serious thinking Jeff Findley wrote :   
   > > In article , jfmezei.spamnot@vaxination.ca   
   > > says...   
   > >>   
   > >> I ask this conceptually, not whether it makes sense or not for SpaceX.   
   > >>   
   > >> How difficult would it be to convert Falcon9 from kerosene/Merlin to   
   > >> Methane/Raptor engines?   
   > >   
   > > Difficult.  Changing the fuel changes pretty much everything.   
   > >   
   > >> is this a question of rebuilding first stage from scratch and only keep   
   > >> the grid fins, landing gear and software?   
   > >   
   > > Rebuild from scratch.  The lower density of liquid methane (430 kg/cubic   
   > > meters) compared to kerosene (775-840 kg/cubic meters) would mean you'd   
   > > need to increase the diameter since Falcon is already pushing the   
   > > fineness ratio close to the limits.  So, you wouldn't be able to reuse   
   > > any of the tooling and couldn't transport the stages with semi-trucks.   
   > >   
   >   
   > Hence Starship and SuperHeavy.   
      
   Exactly!  Things that are different, just aren't the same.   
      
   Jeff   
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