(09.08.24) Given doubts about the safety of the Starliner, NASA is currently examining the possibility of having the two astronauts Butch Wilmore and Suni Williams, who flew to the International Space Station on a Boeing CST-100 Starliner spacecraft, return in early 2025 on a SpaceX Crew Dragon instead.

At an Aug. 7 briefing, NASA officials said they expected to decide in mid-August whether it would be too risky to let the astronauts who arrived at the station on Starliner two months ago return on the same spacecraft. That would mean they would have to stay on the station while Starliner automatically undocked and returned to Earth.

NASA: Return of Boeing Starliner astronauts could be delayed until 2025

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NASA would fly the Crew-9 mission, whose launch was pushed back a day earlier than planned from August 18 to September 24 at the earliest, with two people instead of four. Williams and Wilmore would then return with Crew-9 at the end of the planned mission in early 2025.

NASA is considering this option because of ongoing concerns about the performance of Starliner’s reaction control system (RCS) thrusters. Several thrusters malfunctioned during the spacecraft’s approach to the station in June, though all but one have since been restored.

The uncertainty about the cause of the engine performance loss is the catalyst for ongoing discussions about the safety of the returning Starliner crew, including how the engines will behave upon return or “departure.”

Steve Stich, program manager for commercial crews at NASA

“People really want to understand what’s going on physically and then look at the descent and the warm-up phase. And they want to see if we can translate that to the descent phase and make sure we have good engines.”

Tests conducted last month on RCS engines at NASA’s White Sands Test Facility showed that heating the engines can cause a Teflon seal or valve to expand and be pushed out, restricting fuel flow. Heating the fuel can also cause it to vaporize, reducing engine performance.

In a statement released on Wednesday by Boeing-

“We continue to believe in the Starliner’s capabilities and flightworthiness. Should NASA decide to change the mission, we will take the necessary steps to configure Starliner for an unmanned return.”

Starliner description from Boeing

Boeing’s Crew Space Transportation (CST)-100 Starliner spacecraft is being developed in collaboration with NASA’s Commercial Crew Program. The Starliner is designed for missions to low Earth orbit for seven passengers or a mix of crew and cargo. On NASA service missions to the International Space Station, it will carry up to four NASA-sponsored crew members and time-critical scientific research. The Starliner has an innovative, weld-free structure and can be reused up to 10 times with a turnaround time of six months. It also features wireless internet and tablet technology for crew interfaces.