The first crewed mission of Boeing’s Starliner capsule has been in orbit for more than a month now and still doesn’t have a return date.
Starliner launched on June 5 in the Crew Flight Test (CFT), carrying NASA astronauts Butch Wilmore and Suni Williams to the International Space Station (ISS) for a planned one-week stay. The capsule experienced helium leaks and propellant problems during the journey, however, and engineers are still looking into what caused them – meaning the Starliner has not yet been cleared for launch.
“We’re taking our time on the ground to go through all the data before we decide on the possibility of return,” said Steve Stich, manager of NASA’s Commercial Crew Program, during a press conference Wednesday (10 July).
However, NASA, Boeing and the two CFT astronauts still have faith in the Starliner. During a special media event on Wednesday, for example, Wilmore praised the capsule’s capabilities in orbit during operational checks. “The spacecraft performed extremely well,” he said.
Wilmore also discussed issues with Starliner’s feedback control system (RCS) thrusters during the ISS chase and how the mission addressed them.
“We lost one RCS aircraft, and then another, and then you could say the thrust, the control, the capability was degraded,” he explained. “Thankfully, we had practiced and were certified in manual control, and so we took the manual control for over an hour.
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After arriving at the ISS on June 6, Wilmore and Williams were integrated into the station’s Expedition 71 crew, which, according to Williams, is now unofficially called “Expedition 71+.” Wilmore and Williams have taken over the day-to-day maintenance responsibilities and science experiments, and they have been able to close the gap on a small portion of the station’s remaining tasks. Throughout their mission, the pair have also continued to check Starliner’s multiple systems and anomalies they encountered, which are also being examined by Boeing engineers back on Earth to determine their cause.
Stich highlighted the meticulous approach taken to analyze the data and replicate the spacecraft’s thruster issues during testing at NASA’s White Sands Test Facility in New Mexico. One advantage of the ISS, he said, is its ability to serve as a temporary orbital “hangar,” providing a unique opportunity to understand the Starliner’s long-term performance in space before it is decommissioned.
In addition to the propellant issues, several helium leaks have been identified in the Starliner capsule. “There were a number of specific actions that were identified from both the helium anomalies and the propellant anomalies,” Mark Nappi, Boeing vice president and commercial crew program manager, said Wednesday. “It’s a little over 30 [actions]of which more than half are currently closed.”
“For the helium leak, we hope to bring it to the Starliner mission management team for final resolution later this week,” Stich said. Despite those problems, agency officials said the spacecraft is rated to leave the ISS in the event of an emergency, with all but one of its 28 RCS thrusters cleared for use during re-entry into Earth’s atmosphere.
The decision to extend the Starliner mission has also given ground crews extra time they weren’t expecting. According to Nappi, Amy Decker, of Starliner’s chief engineer’s office, says the additional data they’re getting is “GOOD, in all caps.”
“The more time you have to get more data,” Nappi said, “the more excited [the engineers get].”
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The absolute last Starliner to return with Wilmore and Williams, according to Stich, will be mid-August.
“The big driver is the handoff that we have coming up between Crew-8 and Crew-9, which is in mid-August,” Stich said, referring to SpaceX’s two astronaut missions to the ISS. “So… a few days before that [Crew-9] launch opportunity, we’d have to get Butch and Suni home on the Starliner.”
Ideally, however, they will return home sooner. “We’re really working to track the data and see when is the earliest that we can target for unlocking and lowering,” Stich said. “I think some of the data suggests, optimistically, it’s probably until the end of July, but we’re just going to follow the data one step at a time and figure out when is the right opportunity to take off neck.”
“We have a lot of confidence in the thrusters as they are today,” Nappi said, citing an in-orbit thruster test fire that Starliner conducted while docked at the ISS.
“What we’re doing is just taking the time to make sure we’ve looked under every rock and every stone, and just to make sure there’s nothing else that would surprise us,” Stich added in response.
The CFT follows two previous uncrewed Starliner missions to the ISS. The first, in December 2019, failed to reach the orbital laboratory after experiencing a series of malfunctions. The second, in May 2022, docked successfully but also experienced problems with the thruster.
“We knew there would be some lessons from this flight test,” Nappi said. “We’ve learned a lot from how the hardware works, how our processes work and how we can improve.”
Until now, “there was one thruster that was producing very low thrust that we would disable for the rest of the flight,” Stich explained. The extended stay on the ISS also helps teams prepare the spacecraft for the astronauts’ next operational missions, which are scheduled to last up to six months, starting with Starliner-1 sometime in 2025.
Tests at White Sands during CFT have helped planners look ahead to the first operational mission and how to prevent similar problems with the propellant from occurring.
According to Stich, the Starliner’s thruster pulses fired more frequently than engineers had expected this time.
“What we’re trying to do at White Sands,” he said, “is actually replicate exactly what those pulses were that the propellants saw, and then figure out the heating effects from those pulses, and just to make sure there are no unintended consequences of those pulses.”
Stich said he thinks there is a way to take what the teams have observed with the thrusters during CFT to modify their requirements for future rendezvous and docking maneuvers. “I think that’s the job ahead of us for Starliner-1,” he said.
As the CFT mission continues, the focus remains on ensuring a safe return for Wilmore and Williams. “Starliner is the ‘go to’ for emergency return,” Stich confirmed. The team is working through the process, including a return flight readiness review, to prepare for Starliner’s eventual disengagement and landing.