Two NASA astronauts who traveled to the International Space Station in early June were originally scheduled to return home a few weeks ago to complete a test flight of Boeing’s Starliner spacecraft.
Instead, the astronauts, Butch Wilmore and Suni Williams, will remain on the station for several weeks longer while NASA and Boeing engineers continue to study misbehaving thrusters on the vehicle.
But don’t call the astronauts stuck or stranded, officials said Friday. And there is no mention of a rescue mission.
“We are not stuck on the ISS,” Mark Nappi, Boeing’s program manager for Starliner, said during a news conference on Friday. “The crew is not in danger.”
Steve Stich, the manager of NASA’s commercial crew program, also tried to allay concerns.
“The vehicle at the station is in good condition,” he said. “I want to make it very clear that Butch and Suni are not stranded in space. Our plan is to continue to return them on Starliner and bring them home at the right time.”
Mr. Stich then added that the timing would be right after additional analysis of why five of Starliner’s 28 maneuvering jets were behaving erratically as the spacecraft approached the space station. Starliner’s computers, which were guiding the spacecraft autonomously, were able to compensate with the remaining thrusters.
Four of the five thrusters now appear to be working properly; the other thrusters are not used during the return journey. Mission managers expect Starliner to be able to detach from the space station and take Mr. Wilmore and Mrs. Williams on their return trip from space, but they don’t fully understand what caused the problem.
Fatal disasters in NASA history, such as the loss of the Space Shuttles Challenger and Columbia, have taught mission managers to be cautious and curious when something isn’t quite right.
“I think they’re doing their due diligence,” Wayne Hale, a retired NASA flight director, said in an interview. “Since they are in no rush to get home, it makes a lot of sense to take the time to gather as much information as possible so they can make sure any issues are resolved. That makes a lot of sense, to take your time. “
Mr Nappi gave a similar assessment at Friday’s press conference, saying it was prudent to use the time for additional analysis.
“It would be irresponsible if, when we have the time and want to do more, we didn’t do it,” he said.
Starting next week, engineers will conduct ground tests at NASA’s White Sands Test Facility in California using a thruster identical to the one on Starliner. The firings will reproduce the firings that Starliner performed in space.
That will probably take a couple of weeks, Mr. Stich said. “Then we’ll give engineers a chance to go and look at that thruster,” he said. “This is a real opportunity to investigate a thruster, just like we’ve done in space.”
Engineers cannot directly examine the troublesome thrusters on the spacecraft now orbiting Earth because they are located on the so-called service module. That part is jettisoned during the flight home and burns up in the atmosphere.
“The test will help us understand the performance of the thruster and can give us 100 percent certainty that everything we saw on orbit is OK,” Mr. Stich said. “It’s just one more piece of data that we can have before we actually take the vehicle off track.”
Former NASA officials like Mr. Hale noted that mission managers’ overruling of engineers’ concerns has contributed to previous fatal accidents.
During the launch of the space shuttle Columbia in January 2003, a piece of foam insulation from the external fuel tank broke loose 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 Department of Defense and asked if it had the ability to visually inspect the shuttle for damage.
But managers higher up the NASA chain of command were not curious and told Mr. Hale to withdraw the request for help. He complied.
What no one knew at the time was that the foam impact had blown a hole in the wing. When it returned to Earth, Columbia disintegrated, killing the seven astronauts on board.
“As I look back on it now, certainly in the Columbia case, there were not enough questions asked,” Mr. Hale said. “There was not enough time. And the lesson was clearly learned that you take the time that you have to come up with the most complete answer and answer all the questions that any of the experts might have.”
While NASA and Boeing study the spacecraft, Mr. Stich from NASA, Mr. Wilmore and Mrs. Williams could jump into Starliner to get home in the event of an emergency on the space station. When a dead Russian satellite unexpectedly broke apart 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 remain docked at the space station for 45 days, due to limitations in Starliner’s current battery design. But so far the batteries have performed well and the stay can be extended beyond 45 days, Mr. Stich said.
Starliner isn’t the only problem NASA needs to solve right now. A spacewalk was cut short Monday when water leaked from an umbilical cord connected to a spacesuit while astronauts were in the airlock. Engineers still don’t understand what happened.
“We need to think about it again,” said Bill Spetch, NASA’s operations integration manager for the International Space Station program.
The next spacewalk, scheduled for Tuesday, won’t take place until late July, Mr. Spetch said.