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These grid aerobrakes/drag control moving surfaces, have been used for a while on various aerodynamic designs, and presumably they provide a turbulent airflow, which in some way is more predictable than a laminar one, since it never switches between laminar and turbulent. Assuming that a turbulent behaviour is necessary for booster reentry(?), why does it seem like this design is a copy/paste from the past? Are there any other proposals or tests made for this particular aerodynamic part? (maybe with a different grid scale, no grid at all and a different volume/surface ratio, or a totally different shape)?

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Thanks for the answer, the idea was also to question the simplicity of the falcon 9 concept, amount of moving parts, landing fuel weight. I was wondering if those fins could be longer, deploy slowly to aerobrake, and when subsonic pitch them in order to land in autorotation, with no fuel at all.

aerobrake + autorotation

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The issue seems to be the need for a single control surface (for simplicity) to work at hypersonic speeds, down to subsonic.

Grid fins have been used high speed missles in this speed regime, so why reinvent the wheel. It works, it is well known, they traded off and decided on this design.

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  • $\begingroup$ "Why reinvent the wheel" => correct! Especially in the space industry where "flight proven" and "heritage" are the main keywords. If it ain't broke, don't fix it. $\endgroup$ – ChrisR Mar 31 '17 at 18:17
  • $\begingroup$ @ChrisR Also an industry where shiny new wheels don't get you very far. $\endgroup$ – Cort Ammon May 20 '17 at 4:28
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To answer the edited addition: The mechanics to do something like this would:

  • Add considerable mass to the stage
    • This would prevent the use of the stage for the non-recoverable (all fuel used) launches that I believe are required for geosyncronous orbit insertion
  • Add complexity to the design
    • More points of failure
  • Fail to land safely
    • having read a little about autorotation over on aviation.se, a helicopter performing an autorotation landing needs to pitch up to reduce the vertical speed to within a safe threshold for a landing. Unpowered rotors aparrently cannot generate enough lift to perform a vertical landing. This also requires the helicopter to maintain a significant forward speed. This would make accurate landings more difficult, but more importantly would require the stage to maintain horisontal velocity whilst travelling sideways through the atmosphere, which is not possible due to the large crossection.
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