Officials will also investigate whether a parachute system that Boeing had to rework after an earlier unmanned test flight provides a safe landing in what would be the final act of the Starliner’s first human flight.
After delays caused by a faulty rocket valve and a helium leak in the spacecraft, Starliner lifted off from Cape Canaveral, Florida on June 5 and arrived at the station a day later. As the Starliner approached the station, five of its thrusters, used to make minor adjustments to its trajectory, went offline, forcing Boeing to back the vehicle off the station to fix the problem.
NASA and Boeing were able to bring four of the five back online and land successfully.
Test teams fired the thrusters on Saturday while the spacecraft was attached to the station, and all performed well, NASA said. They didn’t try to test the missile from the one funnel that didn’t come back online during the flight, and they won’t try to use it during the Starliner’s return flight “out of an abundance of caution,” Steve Stich, NASA’s commercial crew program manager, said at a briefing Tuesday.
In addition to the nozzle problems, the Starliner suffered a series of helium leaks in its propulsion system. NASA and Boeing have discovered a new one — the fifth — since the Starliner has been on the station. The leak is small and will not pose a problem for reentry, NASA said. Helium is used to pressurize propellants through the propulsion system.
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NASA originally said the Starliner would return home on June 18, then pushed the landing back to June 22. The problems with the nozzle and the helium leaks are contained in the spacecraft’s service module, which is used to maneuver the capsule during flight. Before the capsule re-enters Earth’s atmosphere, the service module is jettisoned and burns up. That means engineers won’t be able to study it after the flight, which is one reason they said they now need more time to understand the issues.
“We’re taking extra time because it’s a manned vehicle and we want to make sure we leave no stone unturned,” Stich said. “We also want to look at systems and potential interaction between systems and make sure we haven’t missed anything before we go back. And when we’re on the space station, we’re getting a lot of great data not just for this flight, but for the next flight as well.”
NASA and Boeing believe the thrusters were shut down because of the extreme heat generated as they fired “in rapid succession” to keep the capsule on course with the space station, Stich said.
“In some cases, we think the heating may have caused the propellants to vaporize a bit and we didn’t mix well. [of the propellants], and therefore the thrust was slightly lower,” he said. Engineers still don’t understand what causes the helium leaks, he said.
While on the station, Williams and Wilmore prepared for their return and also practiced using the Starliner as a safe haven in the event of an emergency on the space station. They also worked with other astronauts to “install research equipment, maintain laboratory hardware, and help station crew members Matt Dominick and Tracy Dyson prepare for spacewalk,” NASA said in a statement.
Despite the problems, NASA expressed confidence in Starliner. Officials said they expected to discover problems during the mission, a test flight designed to see how the Starliner operates with humans on board.
“We’ve always said it’s a test flight and we’re going to learn some things,” said Mark Nappi, a Boeing vice president who oversees the Starliner program. “So here we are. We have found that our helium system does not work as designed, although it is manageable. … So we have to find out.”
Once the mission is complete, NASA will certify the Starliner for regular flights with a crew rotation of the full contingent of four astronauts to the space station. SpaceX, another participant in NASA’s commercial crew program that outsourced human spaceflight to the private sector after the Space Shuttle was retired, has been flying astronauts for NASA since 2020.
Given the problems the Starliner faced on that test flight, it’s unclear when Boeing, which won a $4.2 billion NASA contract in 2014, will fly its first regular crew-rotating mission.
“We have to deal with helium leaks,” Stich said. “We will not fly another mission like this with a helium leak. Teams also need to figure out what “causes the jets to have low thrust,” he added. “So we have some work to do after this flight.