Two NASA astronauts who traveled to the International Space Station in early June were originally scheduled to return home several weeks ago, completing a test flight of Boeing’s Starliner spacecraft.
Instead, the astronauts Butch Wilmore and Suni Williams will remain on the station for a few more weeks as NASA and Boeing engineers continue to study the vehicle’s misbehaving thrusters.
But don’t call the astronauts stranded or stranded, officials said Friday. And there is no talk of a rescue mission.
“We’re not stuck on the ISS,” Mark Nappi, Boeing’s program manager for Starliner, said during a press conference Friday. “The crew is in no danger.”
Steve Stich, NASA’s commercial crew program manager, also tried to calm concerns.
“The car at the station is in good condition,” he said. “I want to make it very clear that Butch and Suni are not trapped in space. Our plan is to continue to get them back to the Starliner and get them home in due time.”
Mr. Stich then added that the appropriate timing would be after additional analysis of why five of Starliner’s 28 maneuvering planes behaved strangely as the spacecraft approached the space station. Starliner’s computers, which were autonomously steering 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 during the journey home. Mission managers expect the Starliner 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 is wrong.
“I think they’re doing their due diligence,” Wayne Hale, a retired NASA flight director, said in an interview. “Being in no rush to come home, it makes a lot of sense to take the time to gather as much information as possible so they can make sure all the issues are resolved. That makes a lot of sense, to take your time.”
Mr. Nappi offered a similar assessment during Friday’s news conference, saying it was prudent to use the time for additional analysis.
“It would be irresponsible for us, if we have time and want to do more, not to do it,” he said.
Starting next week, engineers will conduct ground tests at NASA’s White Sands Test Facility in New Mexico using a thruster identical to those on the Starliner. The firings will replicate those performed by the Starliner in space.
That will probably take several weeks, Mr. Stich said. “Then we’ll give the engineers a chance to look at that propellant,” he said. “This will be the real opportunity to examine a propellant, just like we’ve had in space.”
Engineers won’t be able to directly examine the struggling thrusters on the spacecraft now in orbit because they’re housed in what’s known as the service module. This part will be ejected on the flight home, burning up in the atmosphere.
“The test will help us understand the performance of the thruster and can give us 100 percent confidence that everything we’ve seen in orbit is OK,” said Mr. Stich. “It’s just another piece of data that we can have before we get the vehicle out of orbit.”
Former NASA officials like Mr. Hale noted that mission managers’ oversight of engineers’ concerns contributed to previous fatal accidents.
During the launch of the space shuttle Columbia in January 2003, a piece of insulating foam from the external fuel tank broke off and hit the left wing of the shuttle. 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 had the ability to 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 agreed.
What no one knew at the time was that the foam blow had blown a hole in the arm. While returning to Earth, Columbia disintegrated, killing the seven astronauts on board.
“Reviewing it, certainly in the case of Columbia, there were not enough questions,” Mr. Hale said. “There was not enough time. And the lesson is clearly learned that you take the time that is available to get the most complete answer and to answer all the questions that any of the experts might have.”
While NASA and Boeing study the spacecraft, Mr. NASA’s Stich said, Mr. Wilmore and Mrs. Williams would be able to board the Starliner to return home in the event of an emergency at the space station. Indeed, when a dead Russian satellite suddenly exploded in orbit on Thursday, they briefly took shelter 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 docked to the space station, due to limitations in the Starliner’s current battery design. But so far, the batteries have performed well and the stay could be extended beyond 45 days, Mr. Stich said.
Starliner isn’t NASA’s only problem to solve right now. A spacewalk was cut short on Monday when water leaked from the umbilical cord attached to a space suit while the astronauts were in airlocks. Engineers still don’t understand what happened.
“We have to go think about it 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 the end of July, Mr. Spetch said.