XPost: sci.space.policy, sci.physics, sci.astro   
   From: fjmccall@gmail.com   
      
   "Robert Clark"  wrote on Sun, 20 Jan   
   2019 11:12:37 -0500:   
      
   >Using the rocket equation you can show the payload of the BFS as an SSTO   
   >using altitude compensating nozzles can be improved from ca. 1 ton to ca. 20   
   >tons(!)   
   >   
   >The task of getting passengers to orbit for the Mars flight, or for the   
   >point-to-point transport role can be accomplished without the large,   
   >expensive first stage booster.   
   >   
      
   You understand that the first stage booster is the cheap part of the   
   system, right?  Even if we assume you are correct, Look at how many   
   launches are required to achieve the same mission between the two   
   systems; 300 tonnes to the surface of Mars.   
      
   First let's look at the original system as Musk envisions it.  A   
   single launch puts 300 tonnes in orbit.  You then refuel that ship   
   with three 'tanker' launches, each of which can carry 450+ tonnes of   
   propellants.  Total 'pieces' launched is eight (four boosters, three   
   tankers, and one Mars ship).   
      
   So let's now look at your 'improved' system.  I'll simplify numbers in   
   your favour.  Let's assume your SSTO can boost 20 tonnes (vice 20   
   tons) to orbit).  It takes 15 launches to get 300 tonnes into LEO. Now   
   you need to transfer and consolidate all that cargo into a single Mars   
   ship.  You need to refuel that ship with some 1100 tonnes of fuel and   
   oxidizer.  That's another 55 launches.  Total pieces launched is *70*   
   with the added complication of having to do a bunch of on orbit cargo   
   and personnel transfers.   
      
   And that's being generous and assuming the dry mass of your Mars ship   
   is preposterously low.   
      
      
   --   
   "Some people get lost in thought because it's such unfamiliar   
    territory."   
                                         --G. Behn   
      
   --- SoupGate-Win32 v1.05   
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