Here's why a Japanese billionaire just canceled his lunar flight on Starship

The main technological milestones that SpaceX's Starship needed to achieve before the dearMoon mission could take place included:

1. Safe launch: Demonstrating the ability to launch Starship safely from Earth.
2. Controlled flight in space: Ensuring the Starship could navigate and maintain its trajectory in space.
3. Safe landing of the Starship upper stage: Successfully landing the Starship's upper stage back on Earth after completing its mission.
4. In-space refueling: Testing and perfecting the capability to refuel the Starship while in orbit, which is crucial for long-duration missions like the dearMoon project.
5. Habitability in space: Ensuring the Starship provided a safe and comfortable environment for humans during extended space travel, including life support systems, radiation protection, and living quarters.
6. Propulsion systems: Developing and testing the Raptor engines, which power the Starship, to ensure their reliability and performance for the mission.
7. Heat shield and thermal protection: Designing and testing the heat shield to protect the spacecraft and its passengers during atmospheric reentry.

These milestones were essential for the Starship to successfully complete the dearMoon mission, a private circumlunar flight project. However, due to developmental delays and changes in the financial situation of the project's financial backer, Yusaku Maezawa, the mission was ultimately canceled.

The original launch target year for the dearMoon project as planned in 2018 was 2023.