The Falcon 9 launch system, developed by SpaceX, is considered to be one of the most significant technological achievements in the history of rocket engineering, primarily due to the recoverability and reusability of its first stage boosters. Reusability is a key element to SpaceX’s aim of increasing the reliability and reducing the cost of spaceflight.
The first stage of the Falcon 9 launch system incorporates nine Merlin engines and aluminum-lithium alloy tanks containing liquid oxygen and rocket-grade kerosene (RP-1) propellant. Low-density Airware 2195-T8 plate used in the tank barrels and domes of the booster is supplied by Constellium (formerly Alcan Global ATI). The combination of aluminum-lithium sheet and plate coupled with friction stir welding (FSW) enables the use of thin sections in these stability driven components within the rocket. The weight reduction achieved provides the possibility of an increased payload (about 10 tons to low earth orbit and 5 tons to geostationary orbit). A look at the evolution of Airware technology for use in space launch and crew module applications here.
A number of specific technologies were developed by SpaceX that ensure the accuracy of the Falcon 9’s first stage booster as its lands, as noted in a video from Art of Engineering. Among these technologies are deployable aluminum or titanium grid fins and carbon fiber and aluminum landing gear that help to provide a level of control and maneuverability to the first stage of the rocket during its trip back to Earth. While in the Earth’s upper atmosphere, the first stage is maneuvered using cold gas thrusters to bring it into a controlled descent. As it descends back into the lower atmosphere, the grid fins deploy. These are used like wings, helping to guide the stage down to its landing location. The aerodynamic control surfaces of grid fins provide precise control of the rocket’s position and orientation prior to landing, making them primarily responsible for the 10 m landing accuracy of the first stage booster.
In order to be able to land the first stage in a vertical position, it deploys landing gear comprised of carbon fiber and aluminum. The total span of the landing gear system is approximately 18 m and weighs less than 2,100 kg.
Since the launch of the first iterations of the Falcon 9 rockets in 2010, first stage boosters have been landed and recovered 38 out of the 45 attempts. Of these, 18 recovered boosters have been refurbished and subsequently flown a second time, including B1046 and B1048 boosters, which conducted three missions.