Boeing Corporation announced that the launch of the first manned CST-100 Starliner to the International Space Station has been postponed once again. It will take place on May 21st at the earliest.

The launch of Boeing’s CST-100 Starliner reusable spacecraft was supposed to take place on May 6, but was canceled two hours before launch. Engineers at United Launch Alliance (ULA) discovered a technical fault in the Atlas V rocket’s upper stage oxygen valve that caused it to hum and vibrate, leading experts to question the safety of the mission.

Then the engineers decided not to repair the valve, but to replace it completely. Therefore, the rocket was sent to the assembly workshop and the launch was postponed until May 17. However, on May 14, engineers discovered a small helium leak in the Starliner service module, and the ship’s launch was postponed, this time until May 21.

The unmanned Starliner has flown to the ISS twice before. However, in December 2019, it was unable to dock with the orbital station due to engine malfunction and returned to Earth ahead of schedule. Later in May 2022, the Starliner mission was declared a success, although not without problems.