than planar fins, as they are effectively a group of short fins mounted parallel to one another. Their reduced chord reduces the amount of torque exerted on the steering mechanism by high-speed airflow, allowing for the use of smaller fin actuators, and a smaller tail assembly overall. 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. At high Mach numbers, grid fins flow fully supersonic and can provide lower drag and greater maneuverability than planar fins. Application in reusable launch vehicles Grid fins are used on the Falcon 9 rocket for increased precision and accuracy in control of the landing location for reusable launch vehicles. It therefore helps the rocket to land on the landing pad or on the autonomous spaceport drone ship more precisely with good accuracy. The grid fin development effort is a part of the SpaceX reusable launch system development program that has been underway since 2012. The first hypersonic flight test with grid fins was in February 2015, and grid fins were subsequently used on all reusable Falcon 9 experimental test landings and, eventually, after December 2015, an increasing number of successful first stage landings and recoveries. Iteration on the design of the Falcon 9 grid fins continued into 2017. 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. Falcon 9 Block 5 introduce new cast and cut titanium grid fins. Musk had noted the original Falcon 9 grid fins were made from aluminum. The fins experience temperatures near their maximum survivability limits during reentry and landing, and so the aluminum fins were coated with an ablative thermal protection system. In fact, some aluminum grid fins have actually caught fire during the entry and landing sequence. The new titanium grid fins should introduce greater controllability to the rocket and increase the payload to orbit capability by allowing Falcon 9 to fly at a higher angle of attack. The larger and more robust titanium grid fins are left unpainted and were first tested in June 2017. They are used on all reusable Block 5 Falcon 9 first stages since late 2017. Gallery References External