Boeing’s Starliner CFT Docks with ISS Despite Thruster Issues

Boeing’s Starliner CFT Docks with ISS Despite Thruster Issues

Boeing’s Starliner commercial crew spacecraft docked at the International Space Station this afternoon, but not without drama. First, more helium leaks emerged once Starliner was in orbit, and then docking was delayed when some of Starliner’s thrusters went offline. Boeing and NASA officials concede they do not have all the answers, but are confident Starliner is perfectly capable of safely returning NASA’s two astronauts to Earth.

The Starliner Crew Flight Test (CFT) lifted off on the third try from Cape Canaveral Space Force Station yesterday at 10:52 am ET. Butch Wilmore and Suni Williams, experienced NASA astronauts and Navy test pilots, were finally on their way back to the ISS. Both have spent long-duration missions there in the past.

NASA astronauts Barry “Butch” Wilmore and Sunita “Suni” Williams wave goodbye to well wishers as they leave crew quarters enroute to the launch pad for the third attempt to launch the Starliner Crew Flight Test, June 5, 2024. This time was the charm and they lifted off at 10:52 am ET. Photo credit: NASA/Joel Kowsky

By evening yesterday, however, they were informed that more helium leaks were being detected in the Reaction Control System (RCS) thrusters needed for in-orbit maneuvering. A helium leak in one of the 28 RCS thrusters was partially responsible for delaying the launch from May 6 to June 1, but Boeing and NASA reported that leak had stabilized before yesterday’s launch.

On top of that, today five of the thrusters went offline when software automatically disabled them for reasons that are not yet understood. Boeing reset four of the five by hot-firing them, but one remains nonfunctional.

Troubleshooting the thruster malfunctions delayed Starliner’s arrival at the ISS. Butch and Suni missed their 12:15 pm ET docking opportunity, but got there on the next one at 1:34 pm ET. After leak checks and other procedures, at 3:45 pm ET they floated into the ISS and the welcoming arms of their seven new crewmates: NASA astronauts Tracy Dyson, Jeanette Epps, Matt Dominick and Mike Barrat, and Roscosmos cosmonauts Oleg Kononenko, Nikolai Chub, and Alexander Grebenkin.

They will remain on the ISS for at least eight days, but NASA has not decided exactly when they’ll return home. The first opportunity is June 14, but they might stay longer. Butch and Suni are two extra pairs of helping hands for a number of tasks including replacing a urine processing assembly that failed unexpectedly. They brought a replacement with them.  On the ISS, urine is distilled into potable water, which not only sustains the crew — yesterday’s coffee is tomorrow’s coffee as many of them say — but reduces the volume of waste that must be discarded. With nine people onboard, it’s very important to have a functioning unit.

Boeing and NASA are confident the helium leaks and thruster problems are not an impediment to their return.  During a post-docking news conference this afternoon, NASA Commercial Crew Program Manager Steve Stich and Boeing Vice President and Program Manager for Commercial Crew Mark Nappi downplayed the malfunctions as just part of the process of testing the spacecraft for the first time with a crew aboard.

Starliner has flown twice without a crew. The first Orbital Flight Test (OFT) in December 2019 uncovered serious defects. Boeing decided to refly the uncrewed test before putting people on board. It was two-and-a-half years before that second flight, OFT-2, successfully took place in May 2022. Now they are testing it with a crew.

Stich and Nappi conceded they do not understand the underlying cause of the helium leaks or the thrusters that are being automatically taken offline.

The first helium leak was in a flange in one of the RCS thrusters. Discovered before launch, Boeing and NASA decided the leak rate was manageable and Starliner could launch as is. But now the spacecraft is in orbit, three other leaks have been detected.  Once Starliner docked to the ISS, the manifolds were closed so nothing is leaking at the moment and there is plenty of helium for deorbiting the vehicle, so they are not concerned for this mission, but want to find out the root cause for future flights.

Similarly, they do not understand why five of the RCS thrusters went offline. They were able to restore four of the five, but one remains nonfunctional. Nappi stressed it is not a hardware problem, the thrusters themselves are fine. Nor is it a software problem per se, but rather how Boeing set it up.

Mark Nappi, Boeing Vice President and Program Manager, Commercial Crew, June 6, 2024 Starliner CFT post-docking news conference. Screengrab.

“The thrusters worked great. And by re-firing them we proved that. So it’s the conditions that we’ve put in the software that is somehow telling the thruster to be deselected.  It doesn’t fail, it has been deselected. And that’s not a software problem. That’s the data we’re putting into the software that needs to be understood a little bit more so that we can not deselect those thrusters and keep them operating.” — Mark Nappi, Boeing

Stich and Nappi insisted problems like this are not unexpected on the first crewed flight of a new vehicle. Starliner is only the sixth human spacecraft in the history of the U.S. space program after Mercury, Gemini, Apollo, the Space Shuttle and SpaceX’s Crew Dragon.

Nappi said he began working on the shuttle program around 1985 when there had been 20-25 flights and a lot was still being learned. Compared to this first crewed flight of Starliner: “We have two problems on this vehicle right now. The helium leak and figuring out how to fine tune these thrusters so that they’re not selected off. Those are pretty small, really, issues to deal with and we’ll figure them out for the next mission. So I don’t see these as significant at all.”


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