From: jfindley@cinci.nospam.rr.com   
      
   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.   
      
   > Or just change engine mounts, and use the LOX tank design onto the   
   > methane fuel tank ?   
      
   See above.   
      
   > Since the Raptor engines are already designed/tested, they already have   
   > the tooling to make engines, and the fuselage for Falcon9, the software,   
   > grid fins, landing gear, and interafce to stage2, just curious whether   
   > it would represent an order of magnitute similar to building new rocket   
   > or whether it would be relatively minor % of developping from scratch.   
      
   Pretty much redesign from scratch.   
      
   > And more generically from a market point of view: Will starship   
   > obliterate the demand for smaller launchers such as Falcon9, or will   
   > customers still want "their own" smaller launcher to get to their   
   > desired obrit on their own timing without requiriong cooprdination with   
   > many other customers who also want same orbit and are ready with their   
   > payloads at same time?   
      
   Time will tell.   
      
   Jeff   
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