Why SpaceX Changed Its Falcon 9 Landing Strategy: On Land vs. On a Drone Ship

In broad terms, why did SpaceX switch from landing Falcon 9 first stages on a drone ship to landing them on the ground? This is a critical question for anyone interested in the future of space technology.

The Current Landscape: Only SpaceX and Future Plans

Firstly, it is important to note that currently, SpaceX is the only entity landing boosters. While several other companies have announced their plans to implement such landings in the future, none have succeeded in doing so as of now.

The Drawbacks of Traditional LANDING Methods

In comparison to the traditional approach of expending the booster after a single flight, any recovery method will add to the mass of the booster, thereby reducing its performance for the primary mission. For SpaceX's approach, increased 'dry mass' comes from landing legs and grid fin control surfaces. Additionally, there is a need to reserve propellant for engine burns after the separation of the upper stage.

SpaceX operates its rockets in three different modes:

Completely Expended: This is the traditional method, where the extra dry mass to be omitted, and no fuel reservation is needed, thus providing maximum performance at the highest cost. Down-Range Landing on Droneship: This requires the extra dry mass plus a modest fuel reservation for the reentry and landing burns, leading to a reduced performance and an additional cost for marine operations along with extra turnaround time for the voyage back to the launch site. Landing on Ground Near Launch Site: This method requires about double the fuel reservation for an additional 'boost back' burn to halt the booster in space and then set it moving on a reverse trajectory back towards land. Although this minimizes cost, it also reduces mission performance.

Strategic Choices: Starlink Satellites and Safety Considerations

SpaceX's decision to switch landing strategies was significantly influenced by the Starlink satellites' launches. Given that they can easily reduce the number of satellites per launch to enable a return to the launch site, it suggests that landing on a drone ship is overall more cost-effective. This is further supported by the fact that all US launches range over the oceans for safety reasons, making landings at sea the only feasible option.

Conclusion

The shift in SpaceX's landing strategy highlights the complex interplay between cost, performance, and practical considerations. By understanding these factors, we can gain insights into the broader trends in space technology and the ongoing efforts to optimize spacecraft operations for both efficiency and safety.