(8-9-24) NASA is evaluating options to have the two astronauts, Butch Wilmore and Suni Williams, who flew to the International Space Station on a Boeing CST-100 Starliner spacecraft return instead on a SpaceX Crew Dragon in early 2025, given questions about the safety of Starliner.

Suni Williams and Butch Wilmore

At an August 7th briefing, NASA officials said they expect to decide around the middle of August if it is too risky to have the astronauts who arrived at the station two months ago on Starliner, to return on the same spacecraft. That would require them to stay on the station while Starliner performs an automated undocking and return to Earth.

Boeing Starliner astronauts’ return could be delayed until 2025: NASA

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NASA would fly the Crew-9 mission, whose launch was delayed one day earlier from Aug. 18 to no earlier than Sept. 24, with two people instead of four. Williams and Wilmore would then return with Crew-9 at the end of its scheduled mission in early 2025.

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

Uncertainty about what caused the thrusters’ performance to drop is driving the ongoing discussions about the safety of returning crew on Starliner, including how the thrusters will perform on the return or “downhill” phase.

Steve Stich, NASA commercial crew program manager

“People really want to understand the physics of what’s going on and then look ahead to the downhill phase and the heating phase, and seeing if we can model that on the downhill phase and ensure that we have good thrusters.”

Tests performed on RCS thrusters last month at NASA’s White Sands Test Facility showed that heating of the thrusters could cause a Teflon seal or poppet to expand and extrude, restricting the flow of propellant. Heating of the propellant could also cause it to vaporize, reducing thruster performance.

In a statement released Wednesday by Boeing-

“We still believe in Starliner’s capability and its flight rationale. If NASA decides to change the mission, we will take the actions necessary to configure Starliner for an uncrewed 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 was designed to accommodate seven passengers, or a mix of crew and cargo, for missions to low-Earth orbit. For 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, weldless structure and is reusable up to 10 times with a six-month turnaround time. It also features wireless internet and tablet technology for crew interfaces.