There were failures in its propulsion system, but Boeing’s Starliner spacecraft and the two NASA astronauts it was carrying docked successfully at the International Space Station on Thursday afternoon.
Docking, at 1:34 p.m. Eastern Time, was more than an hour later than planned after troubleshooting several malfunctioning thrusters.
Starliner’s arrival came a day after the vehicle launched from Cape Canaveral Space Force Station in Florida. The docking was a major milestone for the test flight, which will provide final verification that Starliner is ready to begin operational flights once a year to transport NASA crews for six-month stays at the space station.
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 prevented it from flying the Starliner with people on board.
Engineers expected to encounter problems during this flight, and they did.
Even before launch, a small helium leak was discovered in Starliner’s propulsion system. That led to several weeks of investigation.
Helium, an inert gas, is used to propel the thrusters into the spacecraft’s thrusters. If too much is lost, the thrusters may not function properly.
Engineers determined that the leak appeared to be limited to a seal, but later discovered a “design vulnerability.” Had a series of improbable failures occurred with the propulsion system after undocking, Wilmore and Williams may have been stranded in orbit.
Boeing developed a backup procedure for Starliner to return to Earth in the event of unlikely failures. Boeing and NASA officials decided that the helium leak did not need to be repaired and the spacecraft could be launched.
However, two more helium leaks appeared last night.
Helium flows to the leaking parts of the propulsion system were cut off, and engineers analyzed the problem while Wilmore and Williams slept. In the morning, those responsible for the mission decided to continue with the docking. The helium flow was reactivated for docking maneuvers.
“Starliner currently maintains a lot of helium reserves,” Boeing engineer Jim May said during NASA’s coverage of the Starliner mission. “We expect more than 90 hours of free-flying thruster capability after undocking. “Currently, the helium leak is not a safety issue for the crew or the mission.”
As Starliner approached the space station, four of Starliner’s 28 maneuvering aircraft appeared to be malfunctioning. That led to more troubleshooting and Starliner missed its first opportunity to dock.
The spacecraft and astronauts waited for the next one and then slowly approached without any major difficulties.
It took a couple of hours to open the hatch between Starliner and the space station, after procedures to ensure the seals were airtight. At approximately 3:45 p.m. Eastern time, Williams and Wilmore exited Starliner, greeted with hugs from the other astronauts.