The Starliner is still set to make its historic first flight with astronauts on June 1, but that could change as the team works through “difficult” issues after a small helium leak.
NASA and Boeing officials stressed that they are carefully weighing the decision to launch the first Starliner test mission with astronauts to the International Space Station (ISS). The approximately one-week mission is known as the Crew Flight Test (CFT) and involves NASA astronauts Butch Wilmore and Sunny Williams, both former US Navy test pilots.
“It’s so complicated. There is so much going on. We really just had to work on it as a team,” Ken Bowersox, associate administrator for NASA’s Space Operations Mission Directorate and a former astronaut, told reporters in a teleconference on Friday (May 24). ). He added that it took a long time to resolve the issues, which is part of the reason few updates have come from the team in recent weeks.
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A Delta Flight Readiness Review will be held on Wednesday (May 29) to review the leak and changes where the team can perform an orbit burn if necessary. This is slightly different from the standard airworthiness review because the temporary human certification document for CFT has changed due to this new situation, he added. NASA will then hold another call with reporters on Thursday (May 30), agency officials said.
Starliner was delayed from its May 6 launch attempt, just two hours before liftoff, because of a problem with the oxygen safety valve on the Atlas V rocket designed to launch the astronauts from the Cape Canaveral Space Force Station near Orlando, Florida. United Launch Alliance (ULA), the company that makes the rocket, chose to replace the “buzzing” valve, which opened and closed rapidly.
That valve replacement went on schedule by May 12, but another problem—a helium leak in the Starliner—was discovered after the launch was cleared. Investigating what happened and how to resolve it has forced launch dates to be pushed back several times, most recently to no earlier than June 1st.
During the teleconference, NASA and Boeing officials said that if the Starliner leak had occurred in space, they would have found ways to deal with it there; they stressed that the leak was small and that hardware could fail unexpectedly even on fully certified spacecraft systems.
“There’s not a human-rated vehicle that doesn’t experience this kind of anomaly,” said Boeing’s Mark Nappi, vice president and program manager of the company’s commercial crew program. (Other parts of the press conference gave examples from SpaceX’s Crew Dragon, also used for commercial crewed flights, and the retired Space Shuttle program, which used for NASA launches.)
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Helium, as a non-inert gas, does not pose an immediate launch risk. But because it’s part of the Starliner’s propulsion system, it can affect pressurization for small maneuvers in orbit. In addition to investigating this leak, NASA and Boeing are working to learn how the helium system could potentially affect the Starliner’s return to Earth.
The leak is located in one thruster of Aerojet Rocketdyne’s Reaction Control System (RCS), which is located in a “dog house,” one of four such assemblies around the outside of the Starliner’s service module. It’s in a manifold that “is used to open and close valves on each of the thrusters,” said NASA’s Steve Stich, program manager for the agency’s Commercial Crew Program.
He said the situation prompted the Starliner team to pay more attention to the collectors; while NASA says preliminary inspections have been robust, “perhaps in a perfect time frame. We may have identified this earlier.” But that’s exactly the role of a test flight, to identify such problems, he noted.
NASA, Aerojet Rocketdyne and Boeing are evaluating about five solutions to prevent the leak from reoccurring on future missions. Even then, Stitch added, “Helium is a small molecule. It tends to leak.”
The leak started at 7 pounds per square inch (psi) and increased to between 50 psi and 70 psi, coming from an area the size of a button on the Starliner spacecraft, which is less than 10 sheets of paper. (Engineers couldn’t safely open the leak while the Starliner was stacked on its Atlas V at ULA’s Vertical Integration Facility, so instead they analyzed the leak using software tools.)
The leak is from a rubber gasket that’s between two metal parts of a flange that “keeps that interface tight so the helium can pass through,” Stich said.
The remaining 27 thrusters in the RCS are not leaking at all, he stressed, and the analysis found that the Starliner could handle four more thruster leaks — or a leak up to 100 times larger in that area. Engineers also tested the system through several pressure changes, and the leak was “relatively stable” through those changes, he said.
Stich said studying the helium leak revealed a “design vulnerability” in the propulsion system. There are three certified techniques in which the Starliner can return home: Eight RCS thrusters, two Orbital Maneuvering and Attitude Control (OMAC) thrusters, or four OMAC thrusters.
But under the “right circumstances of failures”, meaning the loss of two thruster manifolds in adjacent doghouses, they could lose the ability to fire eight RCS jets at once and thus also lose a form of backup.
“So we wanted to take extra precautions to figure out what could we do if we lost our engines?” We worked with the engine supplier [Aerojet Rocketdyne]Boeing and our NASA team come up with a redundant method to handle your burn: Split it into two burns, about 10 minutes each [and] With an interval of 80 minutes to exit with a deorbital burn with four RCS thrusters and regain the capability of the original system.
“And it took a little time for our team to work,” he continued, saying it included NASA teams in guidance and navigation, structures and propulsion along with teams from Aerojet Rocketdyne and Boeing. “So we restored that redundancy for the spare capability in a very remote set of failures for the deorbit burn.”
The crew successfully tested this scenario in a simulator recently, presumably one of the high-quality ones at NASA’s Johnson Space Center in Houston (where they remain in quarantine). That change in booking, however, is one of the main drivers behind Delta’s upcoming May 29 Flight Readiness Review to review Starliner’s human certification, Stich said. The team also wanted to take time to investigate the helium leak and any fixes after taking a break this Memorial Day weekend.
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June 1 isn’t a lock as work is still ongoing, but there are several fallback dates in the near future: June 2, June 5, and June 6 are short-term possibilities for Starliner launches, and there are other chances at the beginning of the summer.
The Starliner will remain stable long after that, Nappi said. But the Atlas V rocket has some parts that will expire in June and July, said ULA’s Gary Wentz, who is vice president of government and commercial programs. Other launches may also need to be changed if the delay continues.
The CFT is only allowed to dock at one port on the ISS’s Harmony module, but “we’re pretty flexible all summer long” if the Starliner needs to dock, ISS program manager Dana Weigel told Space.com during the press conference.
As is true for all launches, the CFT will not be scheduled to arrive at the ISS on docking, undocking or spacewalk days, but that port may remain empty at least until crew rotation activities in August, she said. Earlier that month, the Northrop Grumman Cygnus will dock at a separate port on the ISS, and if CFT astronauts are on station at that time, they can help with offloading activities, weather permitting.
Williams and Wilmore will return to the Kennedy Space Center in Florida, where quarantine facilities are a few miles from the launch pad, a few days before launch. The current June 1st launch will see them return on May 28th.
The crew has been in quarantine for about a month, waiting out the delays, but they are “in good spirits,” Bowersox said. Wilmore and Williams attended the meetings remotely and, among other comments, urged the team to move, he said. (As military astronauts and former US Navy test pilots, the CFT crew is also used to both long deployments and working on development programs like Starliner, where schedule changes like this are common.)
Boeing is the other supplier for commercial crews besides SpaceX, after they were selected to taxi astronauts in 2014. Crewed flights were originally expected in 2017, but technical problems and funding issues led to delays. SpaceX has sent a dozen missions to the ISS since 2020, borrowing from its Dragon cargo design (first used in space in 2012) to inform the Crew Dragon design.
Starliner, a new spacecraft, has yet to carry astronauts. An uncrewed test flight in 2019 did not proceed as planned; the spacecraft never reached the ISS after a software problem put it in the wrong orbit. The next attempt in 2022 (delayed by the pandemic and after applying dozens of fixes) got there without a problem.
The CFT was delayed again in 2023 after new problems were discovered with the parachutes (which carried less load than expected) and cables (covered with flammable tape). Those problems are behind the team, Boeing and NASA have emphasized repeatedly in recent weeks.
