From: niklas.holsti@tidorum.invalid   
      
   On 2021-06-28 23:47, JF Mezei wrote:   
   > On 2021-06-28 15:34, Niklas Holsti wrote:   
   >   
   >> During Falcon 9 landing, roll must be controlled by the grid fins and/or   
   >> by thrusters.   
   >   
   >   
   > In final stage, is there sufficient vertical speed for grid fins to have   
   > any aerodynamic control?   
      
      
   Obviously the grid fins stop working when the vertical speed goes to zero.   
      
      
   > Or is that something that MUST be done before it slows down and hope   
   > the roll doesn't change in the last seconds of flight?   
      
      
   On the Falcon 9 booster where the grid fins locked into a position that   
   caused a rapid roll, when the booster slowed down for its ocean landing,   
   the torque from the grid fins also decreased, and I believe the   
   thrusters were increasingly able to overcome that torque, and thus the   
   roll-rate decreased before the "landing".   
      
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