The Space Reviewin association with SpaceNews

Boeing’s CST-100 Starliner docked to the International Space Station. Originally planned to spend as little as eight days there, the spacecraft may remain there for more than a month while engineers study thruster and helium leak issues. (credit: NASA)

Starliner struggles

Bookmark and Share

If you have to repeatedly state that the astronauts you launched to the International Space Station are not “stranded” there, then maybe you have a problem with either your spacecraft or your communications strategy. Or both.

That’s the situation NASA and Boeing find themselves in nearly a month after the launch of the Crew Flight Test (CFT) mission of Boeing’s CST-100 Starliner on June 5. The spacecraft docked with the station a day later and its crew, veteran NASA astronauts Butch Wilmore and Suni Williams, have been on the station since then, doing checkouts of the vehicle while also assisting the station crew in various ways (including Wilmore being an “IT guru” to fix a laptop, NASA officials said at one point.)

“We feel very confident in the thrusters and the team is just making sure to go look at the thrusters in detail across the whole flight,” Stich said June 18.

However, Starliner’s trip to the station was not trouble-free. Before the launch there was already one helium leak in the spacecraft’s propulsion system, which engineers at the time blamed on a damaged seal that they concluded was an isolated problem (see “Star-crossed liner”, The Space Review, June 3, 2024). However, after reaching orbit, controllers reported two more helium leaks with the spacecraft, followed by two more, albeit much smaller, ones after the spacecraft docked.

The leaks themselves don’t pose a risk to the crew: they only exist when the propulsion system is activated, and both NASA and Boeing have reiterated there is more than enough helium needed for Starliner to undock and return to Earth. At the most recent briefing Friday, Steve Stich, NASA commercial crew program manager, said they had ten times the helium needed for the planned set of undocking and deorbiting maneuvers.

But what causes the helium leaks remains unclear. Stich noted at a June 18 briefing that the leak rates declined during thruster tests after Starliner docked with the station. “What it tells us is that there’s got to be some kind of effect” from the thrusters, Stich said, either thermal effects from the firing thrusters or wear on the seals from sliding surfaces in the propulsion system.

He noted the propulsion system has lower demand from undocking and deorbiting than during approach and docking. “That’s giving us some confidence relative to managing the system.”

The helium leak measurements came during thruster tests prompted by the other major issue reported with the spacecraft as it approached the ISS. During that approach, the spacecraft computer “de-selected” or turned off five reaction control system (RCS) thrusters whose performance was not matching its requirements. That briefly delayed the docking while controllers worked to get four of them back online.

Engineers have now spent weeks trying to understand what happened with those thrusters. The tests of the thrusters after docking, Stich said, showed all but one appeared to be working well. The exception is one that was not restored during the approach to the station and showed what he called a “strange signature” in testing, producing almost no thrust.

“Coming out of that, we feel very confident in the thrusters and the team is just making sure to go look at the thrusters in detail across the whole flight,” he said at the June 18 briefing. What caused the thrusters to be de-selected wasn’t clear, but one leading explanation is the intensity of operations by those thrusters during the approach to the ISS may have temporarily degraded their performance.

At the time, that work was scheduled to wrap up in a few days, allowing NASA and Boeing to move on to preparations for Starliner’s undocking and landing at White Sands, New Mexico, early June 26.

But late Friday, June 21, NASA announced the landing would be delayed. “We are letting the data drive our decision making relative to managing the small helium system leaks and thruster performance we observed during rendezvous and docking,” Stich said in a statement NASA released after 8 pm Eastern that evening.

“We understand these issues for a safe return,” said Nappi. “But we don’t understand these issues enough yet for us to fix them permanently.”

NASA did not disclose a new date for Starliner’s return in that statement, saying only that it would take place after the second of two planned spacewalks at the station then scheduled for July 2. (That spacewalk has since been postponed to late July after a water leak from a suit umbilical line in the airlock just as a June 24 spacewalk was beginning; that spacewalk was scrubbed.)

NASA waited nearly a week, until the afternoon of June 28, for another update on Starliner. At that briefing, the agency said it would further delay Starliner’s return so that it could perform ground testing of a Starliner RCS thruster to try to duplicate the conditions seen by the thrusters that malfunctioned during the approach to the station. Those tests, scheduled to start this week, will last at least a couple weeks.

Stich noted that those ground tests will also enable detailed inspections of the thrusters to see what might be causing the issues, something not possible with thrusters in space on Starliner. Those thrusters are in the spacecraft’s service module, which is jettisoned and burns up in the atmosphere, so can’t be studied after the flight.

“This will be the real opportunity to examine the thruster just like we had in space on the ground, with detailed inspections,” he said.

Doing those tests now, rather than after Starliner returns, gives spacecraft controllers the option to do additional thruster tests on Starliner before undocking and to get as much data out of the spacecraft before it leaves home.

“We understand these issues for a safe return,” said Mark Nappi, Boeing vice president and commercial crew program manager, of the thruster and helium leak problems at the most recent briefing. “But we don’t understand these issues enough yet for us to fix them permanently.”

Officials said there was no rush to bring Starliner, with Wilmore and Williams on board, back home. There were plenty of supplies on board for those two, along with work for them to do on the station. “We have the luxury of time,” said Ken Bowersox, NASA associate administrator for space operations, at the briefing.

But this is where a spacecraft problem becomes a communications problem. When Starliner launched, the CFT mission planned to spend eight days docked to the ISS. There was a possibility that it could be extended if needed, but presumably only by a few days or week or so. The spacecraft, officials said at the time, could stay about 45 days at the station, a limit based on the performance of batteries in the crew module.

“I want to make it very clear that Butch and Suni are not stranded in space,” Stich said.

That return date, though, started slipping four days at a time, a pace driven by landing opportunities for Starliner at locations in the southwestern United States. The first four-day delay was stated as an effort to deconflict with a spacewalk scheduled for the day before, but later slips were linked to work on Starliner itself.

The delays have reached a point where NASA is now revisiting that 45-day limit on Starliner. Stich said on Friday’s call that the batteries have shown nothing so far that would limit their performance or create additional risk if the mission is extended. “The risk for the next 45 days is essentially the same as the first 45 days, so we’ll go update that limit,” he said.

But the series of delays in Starliner’s return, with now an indefinite return date, have created a narrative that Williams and Wilmore are “stuck” and “stranded” in space, to cite two words commonly used in media reports in the last couple of weeks around the world. That included speculation about scenarios where SpaceX would be called in to rescue the astronauts on a Crew Dragon.

Even the head of the Indian space agency ISRO, which has zero involvement in the Starliner CFT mission,was asked to comment on the situation, given interest in the country linked to Williams and her Indian heritage. “Getting stranded or stuck in a place is not a narrative that we must have at this moment,” S. Somanath said. “The question today when we develop a spacecraft like the Starliner should be whether it can operate reliably for onward and return journeys. This I believe is what the agencies concerned are thinking.”

Stich said at the start of Friday’s briefing that he wanted to clear up those misperceptions. “I want to make it very clear that Butch and Suni are not stranded in space. Our plan is to continue to return them on Starliner, and return them home at the right time. We have a little bit more work to do to get there for the final return, but they’re safe on the space station, their spacecraft is working well and they’re enjoying their time on the space station.”

Nappi, a little later in the briefing, turned from clearing up misperceptions to airing complaints about media coverage he gets daily about the mission. “Every morning I sit and I read them and, I tell you, from being a representative of Boeing and a representative of the Starliner program, they’re pretty painful to read,” he said. “We’ve gotten a really good test flight that’s been accomplished so far and it’s being viewed rather negatively."

That prompted pushback from reporters on the call, who criticized NASA and Boeing for the limited flow of information about the mission and called for more frequent and more detailed briefings and updates. NASA would, for example, refer to its blog for updates about the mission; NASA published just three since June 14, the original end date for the mission. The progressive delays looked like moving goalposts, with little explanation for why they were moving and how far they would, or could, move.

That limited information created uncertainties about whether it was safe for Starliner to come back NASA. While officials have said Starliner could be used to bring back Williams and Wilmore in an emergency, they hedged—deliberately or inadvertently—when it came to a normal return.

“Are we willing to put our crew on the spacecraft to bring them home? When it is a contingency situation, we’re ready to put the crew on the spacecraft and bring them home,” Bowersox said Friday. “For the nominal entry, we want to look at the data more before we make the final call to put the crew aboard the vehicle.” He added that there will be a review by agency leadership before NASA decides to conclude the mission.

“Are we willing to put our crew on the spacecraft to bring them home? When it is a contingency situation, we’re ready to put the crew on the spacecraft and bring them home,” Bowersox said. “For the nominal entry, we want to look at the data more before we make the final call to put the crew aboard the vehicle.”

By the end of the call, NASA said it would work to provide more frequent updates about the mission as it tests the thrusters, but didn’t commit to any specifics. “We heard your comments about how we share information and we’ll take them into account. We’ll see what makes sense,” Bowersox said, although he stopped short of more frequent briefings. “I also want to impress upon you that the team is just incredibly busy. It takes a lot of time to prepare for these conferences.”

There will be time, later, for more discussions about the long-term future of Starliner. Nappi, at Friday’s briefing, bluntly rejected the suggestion that Boeing would give up on the program after this test flight. “The plain and simple answer to the question is no, we’re not going to back out. This is our job and this is what we’re going to continue to do to meet our commitment.”

The problems, though, may mean Starliner won’t be ready as previously planned for its first crew rotation mission to the station, Starliner-1, in early 2025. NASA had expected, back when Starliner was going to launch in May, to have the vehicle certified by November to enable those missions, alternating with SpaceX.

Stich said on the call that certification would, not surprisingly, take longer than expected, but stopped short of saying that Starliner wouldn’t be certified in time for that early 2025 mission. At some point NASA will have to decide whether to proceed with those plans or bring up SpaceX’s Crew-10, currently scheduled for late summer of 2025, to that early 2025 launch window.

He said NASA is working on both Starliner-1 and Crew-10 in parallel, giving the agency some schedule buffer. “We can take our time and get through the Crew Flight Test and have the vehicle return with Butch and Suni, and then we can make decisions afterwards,” he said. “We still have time.”

Note: we are now moderating comments. There will be a delay in posting comments and no guarantee that all submitted comments will be posted.