The Landings of SpaceX’s Flacon 9
On August 18th, 2020, SpaceX pushed its achievements to unseen boundaries in the realm of reusable launch systems by successfully landing one of its Falcon 9 boosters for the 6th consecutive time. To that date, SpaceX had already landed a total of 58 times, reused across 40 missions. To clarify, the booster in a Falcon 9 launch vehicle is the bottom section of the rocket, which hosts 9 of its engines and rises to almost 50 meters. To recover the first stages of their boosters, SpaceX lands them on land or at sea on target roughly the size of football fields, but how do they reach such accuracy levels?
In this new age of space launches, reusable launch systems have now become the most viable option, as the reuse of high-cost engines is economically profitable, and is as such exploited not only by SpaceX (landing the launch vehicles Falcon 9, Falcon Heavy, and Starship) but for example also Blue Origin with several of the successful returns of their space tourism shuttle: New Sheppard. According to SpaceX, reusing rockets would alone reduce the cost of a mission from an average of 62 million USD per launch to below 30 million USD.
The first stage (bottom and usually largest portion of the rocket) recovery has always been Elon Musk’s main goal. Since the very beginning, in Falcon 1 launches, he attempted to recover boosters thanks to parachutes. However, this method proved inefficient as boosters would burn upon atmospheric reentry before the parachutes could even deploy. The first experimental prototypes of propulsive landings were developed and flown from 2012 to 2014 to implement them in the next launch vehicles. These developments were all part of the SpaceX reusable launch system development program to privately develop reusable rockets to reduce the cost of access to space. Thus, SpaceX eventually put into place in the Falcon 9 first stages to test controlled-descent vehicles’ concepts.
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Through first stage recovery, SpaceX was aiming at controlled EDL (re-entry, descent, and landing) after space flight and had since 2017 consistently been landing their Falcon 9 missions. The process of development came in two stages. First, SpaceX had the goal of touching down in the ocean, aiming for 0 velocities at impact, and second, to develop landing surfaces at sea on autonomous spaceport drone ships to vertically land their rockets or even on the ground Landing Zones like the concrete pads at Cape Canaveral.
In the course of 2019, it was announced that SpaceX had attempted a total of 47 landings of rocket first stages on a solid surface with a success rate over 80%. SpaceX used grid fins (flight control surfaces often used on ballistic missiles or rockets) to control high-velocity atmospheric reentry to guide Falcon 9’s first stages back to the landing zone. Although they were the first to achieve the landing of an orbital booster, many other rockets now use grid fins, such as Long March 2C, the Chinese rocket, to steer it away from cities upon re-entry.
Although SpaceX faced many failures during the testing stage, with first stages sinking, they successfully landed their first rocket on the ground on December 21st, 2015, making “Flight 20” the first solid surface landing of a first-stage booster.
SpaceX then pushed its ambitions of precision even further, landing its Falcon 9 flights on floating platforms placed at sea. The challenge was to land a first stage booster with a leg span of 18 meters on a platform of 52 meters in width. Also, SpaceX would have to deal with GPS errors and ocean swells, creating the platform’s relative instability compared to ground landing zones. Nonetheless, these drone ships were eventually put into use and made autonomously as well as allowed Musk to unleash his creativity and wit naming them “Just Read the Instructions,” “Of Course I Still Love You,” and “A Shortfall of Gravitas.”
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