From: niklas.holsti@tidorum.invalid   
      
   On 2020-11-28 2:48, JF Mezei wrote:   
   > Saw some video on Youtube that in-orbit refueling of Starship would be   
   > done engine to engice (back to back) as opposed to nose to nose or side   
   > by side.   
      
      
       ...   
      
   > from a refueling point of view, is it just a question of opening a pipe   
   > between 2 tanks and letting pressures equalize? Or would there need to   
   > be a pump in there to "push" as much methane or LOX into the starship   
   > being refueled to empty the fuel "truck" ?   
      
      
   SpaceX have said that they will use small thrusters to create a small   
   ullage acceleration that will move the propellant in the tanker to the   
   bottom of the tank, where the pipe to the tankee starts, so that liquid   
   flows, rather than gas.   
      
   I would assume that a pressure difference between the tanker and the   
   tankee can then be set up to increase the flow of propellant. Some of   
   the propellant would be lost as gas, but perhaps not a large fraction.   
      
       ...   
      
   > Is the refueling still a concept or has SpaceX confirmed how it would be   
   > done?   
      
      
   SpaceX have some NASA contracts to study and demonstrate in-orbit   
   refuelling and in-orbit transfer of cryogenic propellants. I believe   
   that the plan for the first test/demonstration is to transfer propellant   
   between the main tanks and the header tanks within one Starship.   
      
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