From: snidely.too@gmail.com   
      
   JF Mezei pounded on thar keyboard to tell us   
   > On 2021-12-20 16:19, Snidely wrote:   
   >   
   >> The extra engines are not the sea level engines, they are the 3   
   >> additional vacuum engines (RVACs).   You don't need sea level engines   
   >> in LEO, you only need them during launch and landing.  But they are   
   >> still useful in orbit, despite reduced efficiency.   
   >   
   >   
   > Does adding mass for 3 additional engines matter much in the grand   
   > scheme of things? I recall criticism of Space Shuttle having to   
   > accelerate its SSMEs to orbital speed as dead weight since it was OMS   
   > that did the work.   
   >   
   > I gather this is some fancy equation of accelerating with lighter mass   
   > (6 engines) vs accelerating with higher mass ( 9 engines) but greater   
   > thrust.  But those extra 3 engines still have to be lifted from ground   
   > before they kick in.   
   >   
   > Do second stages typically have to throttle back to maintain comfortable   
   > 3G when there are humans on-board?   
      
   Yes.   
      
   > Curious to see if the existing 6   
   > engiunes can reach that 3G easily after being dropped off in semi orbit   
   > bu the booster, or whether they really need those extra 3 to reach 3G.   
      
   It depends on the payload, no doubt.  We'll know more about the 3+3   
   configuration early in the New Year, it seems.   
      
   > In terms of lunar lander, I was under the impression that the "main"   
   > engines would be used for orbital ops, and the "side mounted" thrusters   
   > would be used in proximity of lunar ground (last stage of landingk first   
   > stage of taking off).   
      
   It appears you acquired an accurate impression.  However, that design   
   may still be in play, or it may have been dropped.   
      
   > BTW, if the Raptors can't be used to land on the Moon where regolith   
   > obeys laws of physics (pushed sideways) could they be used to land on   
      
   Pushed sideways is an oversimplification even in vacuum.   
      
   > Mars where the atmosphere causes the dust/rocks to behave more   
   > unpredictably?   
      
   The dust and rocks on Mars still obey the laws of physics.  Details of   
   how to land a large rocket on Mars are still under investigation.  Some   
   of the possibilities have already been discussed here, such as adding   
   aluminum [compounds?] to the exhaust as way to make the landing site   
   less loose.   
      
   /dps   
      
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