\n<\/p>\n
There were glitches with its propulsion system, but Boeing\u2019s Starliner spacecraft and the two NASA astronauts it carried successfully docked at the International Space Station on Thursday afternoon.<\/p>\n
The docking, at 1:34 p.m. Eastern time, was more than an hour later than planned, after the troubleshooting of several malfunctioning thrusters.<\/p>\n<\/div>\n<\/div>\n
Starliner\u2019s arrival came one day after the vehicle launched from Cape Canaveral Space Force Station in Florida. The docking was a major milestone for the test flight, which is to provide a final check that Starliner is ready to begin once-a-year operational flights to ferry NASA crews for six-month stays at the space station.<\/p>\n
NASA hired Boeing to build the spacecraft as one of a pair of replacements for its retired space shuttles, but the company experienced years of costly technical problems and delays that kept it from flying Starliner with people on board.<\/p>\n
Engineers expected to encounter problems during this flight, and they did.<\/p>\n
Even before launch, a small helium leak was discovered in Starliner\u2019s propulsion system. That led to several weeks of investigation.<\/p>\n
Helium, an inert gas, is used to push propellants to the spacecraft\u2019s thrusters. If too much is lost, the thrusters may not work properly.<\/p>\n
Engineers determined that the leak appeared to be limited to one seal, but then they uncovered a \u201cdesign vulnerability.\u201d If a series of unlikely failures had occurred with the propulsion system after undocking, Mr. Wilmore and Ms. Williams could conceivably have been stranded in orbit.<\/p>\n<\/div>\n<\/div>\n
Boeing developed a backup procedure for Starliner to return to Earth if the unlikely failures did occur. Officials at Boeing and NASA decided that the helium leak did not need to be fixed and that the spacecraft could launch.<\/p>\n
However, last night, two more helium leaks popped up.<\/p>\n
Flows of helium to the leaking parts of the propulsion system were turned off, and engineers analyzed the problem while Mr. Wilmore and Ms. Williams slept. In the morning, mission managers decided to continue with the docking. The flow of helium was turned back on for docking maneuvers.<\/p>\n
\u201cStarliner is currently maintaining plenty of helium reserves,\u201d Jim May, a Boeing engineer, said during NASA\u2019s coverage of the Starliner mission. \u201cWe expect over 90 hours of free-flight propellant capability after undocking. Currently, the helium leak is not a safety issue for the crew or the mission.\u201d<\/p>\n
As Starliner approached the space station, four of Starliner\u2019s 28 maneuvering jets appeared not to be working correctly. That led to more troubleshooting, and Starliner missed its first docking opportunity.<\/p>\n<\/div>\n<\/div>\n
The spacecraft and the astronauts waited for the next one, and then made their slow approach without further difficulties.<\/p>\n<\/div>\n<\/div>\n
It took a couple of hours to open the hatch between Starliner and the space station, after procedures to ensure that the seals were airtight. At about 3:45 p.m. Eastern time, Ms. Williams and Mr. Wilmore emerged from Starliner, welcomed with hugs from the other astronauts.<\/p>\n<\/div>\n<\/div>\n