The cold gas thrusters of the Falcon 9 are right in line with the grid fins.

The grid fins deploy immediately after MECO and stay deployed while the cold gas thrusters fire.

And it seems the expelled nitrogen is bound to impinge on the deployed grid fins, which would counter some of the torque gained by expelling that nitrogen. The loss must be very small or they wouldn't do it, but still.

Why, of all locations, should the cold gas thrusters be exactly in line with the grid fins? Why not move them a few feet lower or higher to avoid puffing at the fins?

Old pic below, but relative placement of cold gas thruster pod (center) and grid fins hasn't changed.

enter image description here

  • $\begingroup$ Cool image, can you cite/credit the source? Thanks! $\endgroup$
    – uhoh
    Apr 9, 2021 at 22:12
  • $\begingroup$ The thruster ports seem to be canted slightly downward, rather than horizontal, so with the fins deployed, the exhaust path should be clear, below the fins. $\endgroup$ Apr 9, 2021 at 23:44
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    $\begingroup$ Interesting! I hadn’t thought they’d be canted. But why would they cant them if it gives them less torque? It would solve one issue (firing against the fins) but the downward component of the thrust force wouldn’t produce usable torque (e.g. for pitch control) so it would be wasted energy... it seems? $\endgroup$
    – user39728
    Apr 10, 2021 at 1:07
  • $\begingroup$ I'm pretty sure the answer is going to be "SpaceX is a private company and this is proprietary information". Nevertheless, have you considered the simple answer that there is no space to put them anywhere else? After all, there's another rocket with a giant MVac sticking in that thing. $\endgroup$ Apr 10, 2021 at 4:31


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