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How SpaceX Lands Rockets with Astonishing Accuracy
Published: March 27, 2019
The image shows the hypersonic X-15 aircraft on the left, the Falcon rocket in the center, and the Boeing 737 on the right. All vehicles are to scale. Courtesy of Wikipedia, SpaceX.
The SpaceX Falcon 9 rocket’s ability to land as accurately as it does is due to a combination of multiple technologies and vehicle modifications. Most visible are its cold gas maneuvering thrusters and aluminum or titanium grid fins, both of which are designed to provide some level of control authority and maneuverability to the first stage during its trip within and without Earth’s atmosphere.
At the peak of its trips, the first stage is often completely outside of the vast majority of the atmosphere, meaning that aerodynamic forces are no longer relevant or useful for the vehicle. This is where the cold gas thrusters come in: by carrying their reaction mass with them (the gas), Falcon 9 can maneuver outside of the atmosphere. Once the stage descends into thicker atmospheric conditions, the grid fins deploy and are used like wings to guide the stage down to its landing location, be that on land or at sea.