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Two NASA astronauts who traveled at the start of June to the International Space Station were originally scheduled to return home a couple of weeks ago, completing a test flight of Boeing\u2019s Starliner spacecraft.<\/p>\n
Instead, the astronauts, Butch Wilmore and Suni Williams, will remain on the station for several weeks longer as NASA and Boeing engineers continue to study misbehaving thrusters on the vehicle.<\/p>\n
But don\u2019t call the astronauts stuck or stranded, officials said on Friday. And there\u2019s no talk of a rescue mission.<\/p>\n
\u201cWe\u2019re not stuck on I.S.S.,\u201d Mark Nappi, the program manager at Boeing for Starliner, said during a news conference on Friday. \u201cThe crew is not in any danger.\u201d<\/p>\n<\/div>\n<\/div>\n
Steve Stich, the manager of NASA\u2019s commercial crew program, also tried to allay worries.<\/p>\n
\u201cThe vehicle at station is in good shape,\u201d he said. \u201cI 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 return them home at the right time.\u201d<\/p>\n
Mr. Stich then added that the right time would be after additional analysis on why five of Starliner\u2019s 28 maneuvering jets behaved oddly as the spacecraft approached the space station. Starliner\u2019s computers, which were autonomously guiding the spacecraft, were able to compensate with the remaining thrusters.<\/p>\n
Four of the five thrusters now appear to be working properly; the other thruster will not be used during the trip home. Mission managers expect that Starliner can undock from the space station and take Mr. Wilmore and Ms. Williams on their return trip from space, but they do not fully understand what caused the problem.<\/p>\n
Fatal disasters in NASA\u2019s history, like the loss of the Challenger and Columbia space shuttles, have taught mission managers to be cautious and curious when something is not quite right.<\/p>\n
\u201cI think they\u2019re doing their due diligence,\u201d Wayne Hale, a retired NASA flight director, said in an interview. \u201cBeing in no hurry to come home, it makes a great deal of sense to take the time to gather as much information as possible so that they can make sure that the problems are all fixed. That makes a great deal of sense, to take your time.\u201d<\/p>\n<\/div>\n<\/div>\n
Mr. Nappi offered a similar appraisal during Friday\u2019s news conference, saying it was prudent to use the time for additional analysis.<\/p>\n
\u201cIt would be irresponsible for us, if we have time and we want to do more, not to do it,\u201d he said.<\/p>\n
Beginning next week, engineers will conduct ground tests at NASA\u2019s White Sands Test Facility in California using a thruster identical to the ones on Starliner. The firings will reproduce the ones that Starliner performed in space.<\/p>\n
That will probably take a couple of weeks, Mr. Stich said. \u201cThen we\u2019ll give engineers a chance to go look at that thruster,\u201d he said. \u201cThis will be the real opportunity to examine a thruster, just like we\u2019ve had in space.\u201d<\/p>\n
Engineers will not be able to directly examine the troublesome thrusters on the spacecraft now in orbit because they are located on what is known as the service module. That part will be jettisoned during the flight home, burning up in the atmosphere.<\/p>\n
\u201cThe test will help us understand thruster performance and may give us 100 percent confidence that everything we\u2019ve seen on orbit is fine,\u201d Mr. Stich said. \u201cIt\u2019s just one more piece of data that we can have before we actually deorbit the vehicle.\u201d<\/p>\n<\/div>\n<\/div>\n
Former NASA officials like Mr. Hale noted that mission managers\u2019 brushing aside engineers\u2019 concerns contributed to earlier fatal accidents.<\/p>\n
During the launch of the space shuttle Columbia in January 2003, a piece of insulating foam from the external fuel tank broke loose and struck the shuttle\u2019s left wing. Mr. Hale, who was about to begin a new position as the launch integration manager for the shuttle program, called contacts at the Defense Department, asking whether it had the ability to visually inspect the shuttle for damage.<\/p>\n
But managers higher up in the NASA chain of command were not curious and told Mr. Hale to retract the request for help. He complied.<\/p>\n
What no one knew at the time was that the foam strike had punched a hole in the wing. As it returned to Earth, Columbia disintegrated, killing the seven astronauts aboard.<\/p>\n
\u201cLooking back on it, certainly in the Columbia case, there were not enough questions asked,\u201d Mr. Hale said. \u201cThere was not enough time taken. And the lesson clearly has been learned that you take the time that\u2019s available to get to the most complete answer and answer all the questions that any of the experts might have.\u201d<\/p>\n<\/div>\n<\/div>\n
While NASA and Boeing study the spacecraft, Mr. Stich of NASA said, Mr. Wilmore and Ms. Williams would be able to hop into Starliner to head home in the case of an emergency on the space station. Indeed, 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 struck by a large piece of debris.<\/p>\n
The capsule is currently certified to spend 45 days docked at the space station, because of limitations to the current design of Starliner\u2019s batteries. But so far, the batteries have performed well, and the stay can be extended beyond 45 days, Mr. Stich said.<\/p>\n
Starliner is not NASA\u2019s only problem to solve at the moment. A spacewalk was cut short on Monday when water leaked out of an umbilical cord that connects to a spacesuit while astronauts were in the airlock. Engineers still do not understand what happened.<\/p>\n
\u201cWe have to go think about it some more,\u201d said Bill Spetch, NASA\u2019s operations integration manager for the International Space Station program.<\/p>\n
The next spacewalk, which had been scheduled for Tuesday, will not occur until at least late July, Mr. Spetch said.<\/p>\n<\/div>\n<\/div>\n