Nasa astronaut Sunita “Suni” Williams and her colleague Butch Wilmore will not return to Earth in July as their departure has been delayed again.

The delay follows extensive ground testing and inspections of the Reaction Control System (RCS) thruster on the Starliner spacecraft. The Starliner team is now reviewing the data to ensure a safe return for the astronauts.

The RCS thruster testing at Nasa’s White Sands Test Facility in New Mexico provided critical insights for root cause assessments and helped finalise the flight rationale for a nominal undock and landing.

The team plans to hot fire 27 of the 28 RCS thrusters this weekend while the spacecraft remains safely docked at the International Space Station (ISS). This test aims to verify the thrusters’ performance and gather additional helium leak data, which has remained stable since the spacecraft’s arrival on June 6.

“Our mission was to get the crew to the ISS, and that has been completed. Our mission was to learn from a flight test. Now it’s time to focus on returning the crew safely,” Nappi added.