From: niklas.holsti@tidorum.invalid   
      
   On 2021-06-28 21:06, Jeff Findley wrote:   
   > In article ,   
   > jfmezei.spamnot@vaxination.ca says...   
   >>   
   >> On 2021-06-27 17:02, Jeff Findley wrote:   
   >>   
   >>> Heavy will go up and down like a Falcon 9 booster.  Starship is an   
   >>> entirely different beast.   
   >>   
   >> However, I was wondering if SpaceX has experience in precicely   
   >> controlling roll (is it roll?) so that "arms" would be aligned correctly   
   >> to fall on the cradle.  Has it mentioned wherher Falcon 9 not only lands   
   >> on the X but also with the correct roll?   
   >   
   > Engine gimabling provides roll control.   
      
      
   Not during the Falcon 9 landing burn -- only the center engine is used,   
   so gimballing can control only pitch and yaw.   
      
   During Falcon 9 landing, roll must be controlled by the grid fins and/or   
   by thrusters. Judging from the rolling during the landing that failed   
   (and was "sent to sea") because the grid fins were stuck, both methods   
   can be used for roll control.   
      
   If the Super Heavy uses multiple engines for landing, it can control   
   roll by gimballing.   
      
      
   >> Thinking about it, there is probably little in common between starship   
   >> and super heavy landings in terms of software so probably no attempt at   
   >> evaluating roll.   
      
      
   ISTR that SpaceX will try to avoid using entry burns for the Super   
   Heavy. If so, roll during the entry phase cannot be controlled by   
   enginge gimballing. They will probably want to have a certain roll   
   position before the grid fins can get a grip on the atmosphere, so   
   thrusters will probably be used there.   
      
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