Following its 10-day launch on June 5, the Boeing Starliner encountered helium leaks and engine problems during docking with the ISS on June 6. Boeing and NASA executives emphasized that the spacecraft is stable and ready to leave the ISS in the event of an emergency. But after testing the engines in space, NASA and Boeing decided to spend more time investigating the root cause.

The test campaign will begin July 2 at White Sands Proving Ground in New Mexico to recreate the engines’ performance in flight. The test will last about two weeks, but that’s dependent on the results and more analysis needed after that, so NASA and Boeing don’t yet have a date for Starliner’s return.

“We’re not going to target a specific date until we’ve completed the testing and looked at the fault tree and understood the path to it,” said NASA Commercial Program Manager Steve Stich.

Additional testing and examination of the helium source and five engines (of 28 in the system) showed that the leak had stabilized and most engines were recovering, but NASA and Boeing decided not to use at least one of these engines due to performance issues.

The latest information from Starliner officials came on June 21, suggesting that the landing would take place after July 2.

“When this is all over, we’ll meet up and make sure we’ve done everything we need to understand the problem and the state of the system, and then we’ll get home safely,” said Mark Nappi, Boeing’s vice president. commercial crew program manager. Nappi emphasized that it is not yet possible to say exactly when the return will occur.

While analysis continued on the ground, astronauts Butch Wilmore and Sunita Williams focused their stay on ISS activities such as maintenance. “They know this is a test flight. It was no surprise to the astronauts,” Nappi said of the crew’s comments in Boeing’s final communications from orbit.

Starliner is a new type of spacecraft from Boeing, unlike Boeing’s Crew Dragon, which is based on the Cargo Dragon design from SpaceX, the other commercial crew provider taking astronauts to the ISS. Starliner participated in two unmanned missions in preparation for the CFT after failing to reach the ISS on its first attempt in 2019 due to computer malfunctions.

Dragon, meanwhile, completed one unmanned flight in 2019 and one with astronauts in 2020 before sending crews to the ISS every six months.

Following the COVID-19 pandemic and dozens of fixes, the second unmanned Starliner test flight successfully reached the ISS in 2022, but also encountered engine issues during docking. One of the reasons the CFT was docked for the extra time was to evaluate the service module, which holds most of the fuel since it will be emptied during landing. Future tests could shed more light on why Starliner’s propulsion system failed during the 2022 and 2024 dockings.