Grid fin

In 2014, SpaceX tested grid fins on a first-stage demonstration test vehicle of its reusable Falcon 9 rocket,[2] and on December 21, 2015 they were used during the high-velocity atmospheric portion of the reentry to help guide a commercial Falcon 9 first stage back to land for the first successful orbital booster landing in spaceflight history.

The 1st stage of the private Chinese company i-Space's Hyperbola-1 rocket appeared on July 25, 2019 to be equipped with steerable grid fins for attitude control.

Grid fins perform very well at subsonic and supersonic speeds, but poorly at transonic speeds; the flow causes a normal shockwave to form within the lattice, causing much of the airflow to pass completely around the fin instead of through it and generating significant wave drag.

Grid fins are used on the Falcon 9 rocket for increased precision and accuracy in control of the landing location for reusable launch vehicles.

SpaceX CEO Elon Musk announced in early 2017 that a new version of the Falcon 9 grid fins would improve reusability for the company's vehicles.

The grid fins were replaced with titanium versions, which enabled greater controllability to the rocket and increased the payload to orbit capability by allowing Falcon 9 to fly at a higher angle of attack.