(CNN) – After weeks of troubleshooting and recent testing aimed at replicating problems plaguing Boeing’s Starliner spacecraft, NASA and Boeing officials are still not in a position to set a return date for the two astronauts piloting the vehicle on its inaugural manned test flight.
But engineers finally have some possible answers about what ultimately caused some of the Starliner’s problems during the first leg of its journey, which included helium leaks and boosters that abruptly stopped working en route to the International Space Station.
The revelations came after Boeing and NASA spent the last few weeks working to understand the problem on the ground and pushed plans to conduct some additional tests this weekend, which should serve as “icing on the cake” to understand problems, said Mark Nappi, Boeing Commercial Crew Program manager.
At a site in New Mexico, engineers fired test engines more than 1,000 times, to replicate how the Starliner’s thrusters would have fired as it blasted off into space. They then fired the booster to test various ways the engines could be fired on the way home from space, according to Boeing.
The goal of this test was to better understand why the spacecraft’s thrusters shut down unexpectedly and what dangers (if any) could occur when restarting them.
Officials said that with ground testing they were able to recreate the process by which thrusters deteriorated in space during flight. And the tests may have helped engineers better understand the “root cause” of the problem: Heat buildup inside the boosters may be causing the Teflon seals to bulge and restrict fuel flow.
Those tests “have given us additional confidence to undock upon return,” Nappi said.
The findings also led Boeing and NASA to abandon plans to allow astronauts to manually fly the Starliner spacecraft on the way home, as they had to do momentarily during the trip to the International Space Station. “Some of the manual maneuvers put additional stress on the thrusters,” said Steve Stich, NASA commercial crew program manager.
Still, officials did not say definitively whether the Starliner spacecraft that carried veteran NASA astronauts Butch Wilmore and Suni Williams to the space station would be the same vehicle that brings the astronauts home.
“There are many good reasons to complete this mission and bring Butch and Suni home on the Starliner,” Stich said after noting that NASA has contingency options if the Starliner does not receive approval to bring the astronauts home.
“We have to overcome the process,” he added. “We have another Starliner mission management team that is critical to reviewing all of the booster data we just talked about.”
“Of course, I am very confident that we have a good vehicle to bring the crew back,” Nappi said.
Williams and Wilmore arrived at the International Space Station on June 6 for a mission that was expected to last about a week. As of Thursday, the astronauts had been in space for about 50 days. NASA had previously indicated that Starliner can remain in space for up to 90 days.
Separately, engineers made progress in understanding the helium leaks that hampered the first stage of Starliner’s journey, but Boeing and NASA will closely re-examine that issue during additional testing of the vehicle that will continue this weekend. Stich said.
These tests will include firing 27 of the Starliner’s thrusters while the vehicle remains docked with the International Space Station.
Analysis of ground components—specifically, a version of the Starliner service module that has been in White Sands, New Mexico for three years—showed that helium leaks may be the result of seals that degraded from exposure to propellant vapor, according to Nappi.
“The natural solution to that is to simply change that seal to a material that is not as susceptible” to wear from exposure to propellant, Nappi said, referring to possible changes Boeing may make for future Starliner missions.
However, much remains to be done to determine whether leaks aboard the Starliner, which is already in space, have worsened since the vehicle has been docked at the International Space Station. Since the service module (the part of the spacecraft affected by the helium leaks) was exposed to fuel for so long on the ground, Nappi said this could offer a worst-case scenario idea of the degree of degradation of the seals. .
The effort to understand the helium leak problem is one of the main reasons why NASA and Boeing cannot yet set a return date for Williams and Wilmore, or give a definitive answer about whether the Starliner is ready to bring them. home.
“The key attributes of the flight rationale are really that we understand helium leaks; “We understand the stability of the leaks and how we can handle them if they get bigger,” Stich said, referring to the possibility that the helium leaks affecting the Starliner service module could get worse.
NASA and Boeing plan to conduct a review to plan Starliner undocking, which “could occur as early as the end of next week,” according to Stich.
