WASHINGTON — Boeing’s CST-100 Starliner will return from the International Space Station in September without the two astronauts on board who launched on it in June after NASA concluded thruster problems posed too much risk.
NASA announced Aug. 24 that Butch Wilmore and Suni Williams, the NASA astronauts who flew to the ISS on Starliner’s Crew Flight Test (CFT) mission in June, will remain on the station until next February, with Starliner returning to Earth in early September uncrewed.
Agency officials said at a briefing they reached that decision after concluding they did not understand well enough the performance of reaction control system thrusters that malfunctioned during Starliner’s approach to the station in June. NASA and Boeing have worked since then to determine what caused the drop in performance of the thrusters to see if it would reoccur during Starliner’s undocking and return to Earth.
However, they said they could not resolve all the uncertainties about the thrusters to their satisfaction. “That uncertainty remains in our understanding in the physics going on in the thrusters,” said Jim Free, NASA associate administrator.
Testing of the thrusters at NASA’s White Sands Test Facility in New Mexico was able to duplicate the loss of performance in the thrusters, with inspections revealing a Teflon seal had heated and expanded, constraining the flow of oxidizer to the thruster. But officials said they didn’t know enough about how that was happening to be confident that there would not be problems during time-critical burns during Starliner’s departure from the station and its deorbit burn.
“There was just too much uncertainty in the prediction of the thrusters,” said Steve Stich, NASA commercial crew program manager. “There was just too much risk for the crew, and so we decided to pursue the uncrewed test flight.”
“For me, one of the really important factors is that we just don’t know how much we can use the thrusters on the way back home before we encounter a problem,” said Ken Bowersox, NASA associate administrator for space operations.
Both Bowersox and Stich described the decision to bring back Starliner uncrewed as very close, with Bowersox noting that only in the last week did it become clear to him that having Wilmore and Williams return on Starliner was not feasible. “With more time we might have gotten a lot smarter, but we’re just at the point where we need to bring Starliner home,” he said.
Bowersox added that the decision to perform an uncrewed return was unanimous among the NASA representatives in the review. Boeing, he said, was willing to support either an uncrewed or crewed return. “They believe in their vehicle and they’d be willing to bring a crew home on it.”
NASA Administrator Bill Nelson said at the briefing that there was no political influence on the decision amid speculation about any role that the office of Vice President Kamala Harris, the Democratic nominee for president and chair of the National Space Council, may have played. “I can tell you unequivocally, from a personal standpoint, that politics has not played any part in this decision,” he said. “It absolutely has nothing to do with it.”
The path ahead
NASA now plans to move ahead with an alternative strategy it outlined earlier this month. Starliner will undock from the station without a crew and return to Earth for a landing at White Sands or another location in the southwestern United States. Crew-9 will launch no earlier than Sept. 24 with two of its originally assigned four people on board, freeing up seats for Williams and Wilmore. That Crew Dragon spacecraft will return, as planned, in February 2024.
At the briefing, NASA did not disclose which of the four Crew-9 members currently assigned to the mission — NASA astronauts Zena Cardman, Nick Hague and Stephanie Wilson and Roscosmos cosmonaut Alexsandr Gorbunov — would be retained. “We’re working to finalize those crew assignments and update the training plan,” said Norm Knight, director of NASA’s flight operations directorate. “Those decisions will be made public once they are finalized.”
Both he and Dana Weigel, NASA ISS program manager, said Wilmore and Williams were prepared for a much longer stay on the station. Both have flown long-duration ISS missions previously and got refresher training on ISS operations as part of contingency planning for a scenario like this were their stay would be extended.
“They’ve seamlessly become part of the Expedition 71 crew,” Knight said, referring to the long-term crew currently on the station, “contributing to the important work on board the International Space Station.”
Starliner’s departure will also be modified, Stich said. “We’re going to modify the separation sequence a little bit to get away from the space station a little quicker,” he said. There will also be changes in software configurations on the spacecraft to support a docking without astronauts on board who can monitor operations and make changes. NASA did not announce a specific date for Starliner’s return beyond some time in early September.
Starliner’s future
When Starliner flies again remains uncertain. Officials said they will wait until after Starliner makes its uncrewed return to review what changes are needed to the spacecraft and how to carry them out. That includes if another crewed test flight will be required before NASA certifies the spacecraft for ISS crew rotation missions.
“We have not made a total determination yet of what objectives are in front of us or what we have fulfilled,” Stich said. “I don’t think we have decided on the path yet of another crewed flight test.”
“I wouldn’t rule anything out,” Bowersox added. “We have some options on how we move forward.”
There has been speculation that Boeing, which has already recorded $1.6 billion in losses to Starliner to date, including $125 million announced in July, might walk away from the fixed-price contract rather than incur additional losses. Nelson said he has been reassured by Boeing’s new chief executive, Kelly Ortberg, that the company will continue the Starliner program.
“He expressed to me an intention that they will continue to work the problems once Starliner is back safely,” Nelson said. “We will have redundancy in our crewed access to the space station.” However, he said later in the call that he had not asked Ortberg if the company will be willing to shoulder costs like an additional test flight, “nor would it have been appropriate” to discuss it in that conversation.
There were no Boeing representatives at the briefing. Bowersox said that since the briefing was about a NASA decision, the agency felt it appropriate to have only its officials talk to the media about their decision.
“Boeing continues to focus, first and foremost, on the safety of the crew and spacecraft,” the company said in a brief statement. “We are executing the mission as determined by NASA, and we are preparing the spacecraft for a safe and successful uncrewed return.”
Nelson said he expected that Starliner will fly again with astronauts on board. Asked how certain he felt that was, he responded simply, “100%.”
From eight days to eight months
Wilmore and Williams launched on Starliner June 5 after numerous delays, docking with the station the following day. At the time the mission launched, NASA anticipated keeping Starliner at the ISS for as little as eight days, even providing at a post-launch news conference specific undocking and landing times for a June 14 return of the spacecraft.
However, the thruster problems with Starliner on its approach to the station, along with the detection of several additional helium leaks, led NASA to extend the spacecraft’s stay first by days at a time, then weeks.
By late June, NASA pushed back Starliner’s return to at least the latter half of July to perform ground tests of Starliner thrusters in an attempt to replicate the issues those thrusters experienced on approach to the station. However, by late July NASA pushed back Starliner’s departure to as late as mid-August while continuing studies of the thrusters, including tests of the thrusters on the spacecraft itself while docked to the ISS
Through late July there was no public indication that NASA was considering alternatives to having Williams and Wilmore return on Starliner. ‘I’m very confident we have a good vehicle to bring the crew back with,” Mark Nappi, Boeing vice president and commercial crew program manager, said at a July 25 briefing.
Less than two weeks later, though, NASA officials acknowledged they were now considering scenarios where the two astronauts would instead remain on the ISS while Starliner returned uncrewed. In that scenario Williams and Wilmore would stay on the ISS until February 2025, returning on the Crew-9 Crew Dragon spacecraft whose launch NASA had postponed from Aug. 18 to Sept. 24.
At the previous NASA Starliner briefing Aug. 14, the agency said it had to make a decision on Starliner by the last week of August to plan for the spacecraft’s departure, with or without astronauts on board, and to allow for the Crew-9 launch and Crew-8 return. At that briefing, officials they were still working to model and understand the behavior of the thrusters, with no consensus among officials about whether it was safe for Wilmore and Williams to return on Starliner.
With NASA’s decision to have Starliner return uncrewed, Wilmore and Williams will see their stay on the ISS extended from eight days to more than eight months.
“All the astronauts on station are professionals,” Knight said. Wilmore and Williams have been briefed about the decision to return Starliner without them and supported it, he stated. “It’s disappointing that they’re not coming home on Starliner, but that’s ok. It’s a test flight. That’s what they do and they know those risks going in.”
“We keep them very busy” on the ISS, he added. “They’re part of the crew and they’re doing fine.”
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