Two NASA astronauts who traveled in early June to the International Space Station were originally supposed to return home a few weeks ago, completing a test flight on Boeing’s Starliner spacecraft.
Instead, the astronauts, Butch Wilmore and Sonny Williams, will remain on the station for several more weeks while NASA and Boeing engineers continue to study the vehicle’s malfunctioning thrusters.
But don’t call the astronauts stranded or stranded, officials said Friday. And there is no rescue mission to speak of.
“We’re not stuck on the ISS,” Mark Nappi, Boeing’s Starliner program manager, said during a news conference Friday. “The crew is not in danger.”
Steve Stich, NASA’s Commercial Crew Program manager, also tried to allay concerns.
“The vehicle at the station is in good condition,” he said. “I want to make it clear that Butch and Sunny are not stranded in space. Our plan is to continue to bring them back with the Starliner and bring them home at the right time.”
Mr. Stich then added that the appropriate time would be after further analysis of why five of the Starliner’s 28 maneuvering planes behaved strangely as the spacecraft approached the space station. The Starliner’s computers, which autonomously steered the spacecraft, were able to compensate with the remaining thrusters.
Four of the five thrusters now appear to be working properly; the other thruster will not be used on the journey home. Mission managers expect the Starliner to be able to detach from the space station and pick up Mr. Wilmore and Ms. Williams on their return trip from space, but they don’t fully understand what caused the problem.
Fatal disasters in NASA’s history, such as the loss of space shuttles Challenger and Columbia, have taught mission managers to be cautious and curious when something goes wrong.
“I think they do their due diligence,” Wayne Hale, NASA’s retired flight director, said in an interview. “Since they are in no rush to get home, it makes a lot of sense for them to take the time to gather as much information as possible so they can make sure any issues are addressed.” It makes a lot of sense to take your time.”
Mr. Nappi offered a similar assessment during Friday’s press conference, saying it was prudent to use the time for further analysis.
“It would be irresponsible for us, if we have the time and want to do more, not to,” he said.
Early next week, engineers will conduct ground tests at NASA’s White Sands Test Facility in California using a thruster engine identical to that of the Starliner. The shots will replicate those fired by the Starliner in space.
That will likely take several weeks, Mr. Stich said. “Then we’ll give the engineers a chance to go and see the thruster,” he said. “This will be the real opportunity to explore an engine, just like we’ve had in space.”
Engineers won’t be able to directly examine the troubled thrusters on the spacecraft, which is now in orbit, because they are located on what is known as a service module. This part will be ejected during the flight home, burning up in the atmosphere.
“The test will help us understand the performance of the thrusters and can give us 100 percent confidence that everything we’ve seen in orbit is OK,” Mr Stich said. “This is just one more piece of data that we can have before we actually deorbit the vehicle.”
Former NASA officials, such as Mr. Hale, noted that mission managers ignored the concerns of engineers who contributed to earlier fatal accidents.
During the launch of Space Shuttle Columbia in January 2003, a piece of insulating foam from the external fuel tank broke off and struck the shuttle’s left wing. Mr. Hale, who was about to start a new position as launch integration manager for the shuttle program, called contacts at the Defense Department asking if he could visually inspect the shuttle for damage.
But managers higher up NASA’s chain of command were not amused and told Mr. Hale to withdraw the request for help. He complied.
What no one knew at the time was that the foam blow had blown a hole in the wing. When it returned to Earth, Columbia disintegrated, killing the seven astronauts on board.
“Looking back on it, certainly not enough questions were asked in the Columbia case,” Mr. Hale said. “Not enough time was given. And clearly the lesson is that you take the time you have available to get to the most complete answer and answer any questions any of the experts might have.”
While NASA and Boeing study the spacecraft, NASA’s Mr. Stich said, Mr. Wilmore and Ms. Williams will be able to board the Starliner to return home in case of an emergency to the space station. Indeed, when a dead Russian satellite unexpectedly disintegrated in orbit on Thursday, they briefly took refuge in the vehicle and would have used it if the space station had been hit by a large piece of debris.
The capsule is currently certified to spend 45 days tethered to the space station, due to the limitations of the current Starliner battery design. But so far the batteries are performing well and the standby time can be extended beyond 45 days, Mr. Stich said.
Starliner isn’t NASA’s only problem to solve right now. The spacewalk was aborted Monday when water leaked from an umbilical cord that connects to a spacesuit while the astronauts were in the airlock. Engineers still don’t understand what happened.
“We have to think about it some more,” said Bill Spetch, NASA’s operations integration manager for the International Space Station program.
The next spacewalk, which was scheduled for Tuesday, won’t happen until at least late July, Mr. Spetch said.
