XPost: rec.arts.sf.written, sci.space.policy, sci.physics   
   From: tkoenig@netcologne.de   
      
   Robert Clark  schrieb:   
   >===========================================================   
   > "J. Clarke"  wrote in message   
   > news:vqtogdhisj5bl28visfpnhkoc2li07ggm0@4ax.com...   
   >   
   > On Mon, 28 May 2018 11:30:57 -0700, Fred J. McCall   
   > wrote:   
   >   
   > ...   
   >>>>Note that SpaceX has already acknowledged that the Falcon 9 first stage   
   >>>>and   
   >>>>the BFR stages will have SSTO capability, but with small payload.   
   >>>   
   >>>Source?  And I don't mean some throwaway comment or some blog post by   
   >>>somebody who doesn't work for SpaceX.   
   >>>   
   >>   
   >>Well, he's not exactly an employee but Elon Musk has said that a   
   >>Falcon 9 Full Thrust first stage reaches (a very low) orbit on an   
   >>expendable launch and that they deliberately give it a little boost   
   >>back toward the ground so that it doesn't hang around up there for a   
   >>month or two.   
   >   
   > Source?  Other than a tweet?   
      
   Well, one could try plugging the available numbers into the rocket   
   equation.  I've taken them from   
   http://www.spaceflight101.net/falcon-9-v11.html (accuracy is   
   probably debatable, plus the numbers are old, so a grain of   
   salt is advised).   
      
   Average specific impulse (in seconds, yech) could be a bit more than   
   300 s, let's say v_e = 3000 m/s effective exhaust velocity.   
      
   m_full = 418.8 tons. m_empty = 23.1 tons.   
      
   v_max = v_e * ln(m_full/m_empty) = 8700 m/s.  Probably not quite   
   enough, and certainly not useful (I've left out any payload   
   and the aerodynamic nose cone).   
      
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